chapter 3: transport layer - department of computer … · chapter 3: transport layer ... transport...

1

Chapter 3 Transport LayerOur goals understand principles

b h d learn about transport

l t l i thbehind transport layer services multiplexing

demultiplexing reliable data transfer flow control

ti t l

layer protocols in the Internet UDP connectionless

transport unreliable delivery of segments

TCP connection-oriented transport reliable delivery

Transport Layer (SSL) 3-1

congestion controlp y

of byte stream

10172017

Chapter 3 outline

31 Transport-layer services

35 Connection-oriented transport TCPservices

32 Multiplexing and demultiplexing

33 Connectionless transport UDP

34 Principles of reliable data transfer

transport TCP segment structure reliable data transfer flow control connection management

36 Principles of congestion control


reliable data transfer(my slides for Section 34 do not follow Kurose amp Ross)

congest on control 37 TCP congestion

control

10172017

2

Transport services and protocols provide logical communication

between app processes on different hosts

applicationtransportnetworkdata linkphysical

different hosts transport protocol runs in

end systems (primarily) send side breaks app

messages into segments passes to network layer

rcv side reassembles segments into messages

applicationtransportnetwork


segments into messages passes to app layer

data linkphysical

10172017

Internet transport-layer protocols

unreliable unordered datagram delivery by UDP

f ll f ldquob


network no-frills extension of ldquobest-

effortrdquo IP reliable in-order byte

delivery by TCP connection setup flow control congestion control

networkdata linkphysical





application


congestion control services not available

delay guarantees bandwidth guarantees


physical pptransportnetworkdata linkphysical

10172017

3

Chapter 3 outline









reliable data transfer congest on control 37 TCP congestion

control

10172017

Multiplexingdemultiplexing

deliver received segmentsto correct sockets

Demultiplexing at rcv hostgather data from multiplesockets encapsulate data with h d (l d f

Multiplexing at send host

application

transport

P1 application

transport

t k

application

transport

P2P3 P4P1

processthreadsocket

to correct sockets header (later used for demultiplexing)


network

link

physical

network

link

physical

network

link

physical

host 1 host 2 host 310172017

4

How demultiplexing works

host receives IP datagramssource port dest port

32 bits

It uses IP addresses in layer-3 header amp port numbers in layer-4 header to direct segment to appropriate socket

source port dest port

applicationdata

other header fields


(message)

TCPUDP segment format

10172017

Connectionless demultiplexing

UDP socket identified by two-tuple

IP datagrams from different sourcestwo tuple

(dest IP address dest port number)

When host receives UDP segment directs UDP segment to

k t ith d ti ti t

different sources directed to same UDP socket


socket with destination port number

10172017

5

Connection-oriented demux

Server has welcome and connection sockets

Server may support many simultaneous TCP

welcome socket is identified by serverrsquos IP address and a port number

TCP connection socket identified by 4-tuple source IP address

yconnection sockets with clients each connection socket

and the welcome socket have the same port number in server host

receiving host uses all four values to direct


source port number dest IP address dest port number

four values to direct segment to appropriate connection socket

10172017

Connection-oriented demux (cont)

P1 P1P2

SP 9157 SP 9157

P3

SP 5775DP 80

D-IPCS-IP B

P4


ClientIPB

clientIP A

serverIP C

SP 9157DP 80

SP 9157DP 80

D-IPCS-IP AD-IPC

S-IP B

10172017

6

Chapter 3 outline










control

10172017

UDP User Datagram Protocol [RFC 768] ldquobest effortrdquo service UDP

segments (aka datagrams) may be

Length in bytes of UDP segment including header

32 bits lost delivered out of order

to appl connectionless

no handshaking between UDP sender receiver

each UDP segment


32 bits

Application

length checksum


each UDP segment handled independently of others

Applicationdata

(message)

UDP segment format10172017

7

UDP (more) suitable for interactive

streaming multimedia applications loss tolerant Advantages of UDP min rate required

other UDP uses eg DNS SNMP DHCP

reliable transfer over

no congestion control UDP can blast away as fast as desired

small segment header no connection

establishment (which can add delay)


UDPadd reliability in application layer application-specific

error recovery

simple no connection state at sender receiver

10172017

Internet checksumSender treat segment as a

sequence of 16-bit integers (with checksum field initialized to zero)

Receiver compute 1rsquos complement sum

of received segment (checksum fi ld i l d d)initialized to zero)

add integers using 1rsquos complement arithmetic and take 1rsquos complement of the sum

put result as checksum value into checksum field

detail s d h d

field included) check if computed sum equals

sixteen 1rsquos NO - error detected YES - no error detected

But maybe errors nonetheless More later


detail pseudoheader consisting of protocol no IP addresses segment length field (again) included in checksum calculation

hellip

10172017

8

Internet Checksum ExampleNotes

In ones complement arithmetic a negative integer -x is represented as the complement of x ie each bit of x is inverted

When adding numbers a carryout from the most significant bit needs to be added to the result

Example add two 16-bit integers

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline









reliable data transfer(my slides do not follow Kurose amp Ross)


control

10172017

9

Principles of Reliable data transfer important in application transport link layers top-10 list of important networking topics


Principles of Reliable data transfer important in app transport link layers top-10 list of important networking topics


characteristics of unreliable channel will determine complexity of reliable data transfer protocol (rdt)

10172017

10




10172017

Channel Abstractions

Lossy FIFO channel delivers a subsequence in FIFO order delivers a subsequence in FIFO order example delivery service provided by a

physical link

Lossy reordering duplicative (LRD) channel


channel example delivery service provided by IP or by

UDP protocol

10172017

11

Stop-and-wait ARQ (automatic repeat request)

Error-free operationSender

Time


Receiver ack ack

10172017

Stop-and-wait ARQ Retransmission after timeout Recovery from loss of frame

timeoutretransmission

Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ

Retransmission timeout retransmission

after timeout to recover fromloss of ack

Receiver getsduplicate frame

Sender

Time

Error


Sequence numberneeded in frame Receiver

10172017

Stop-and-wait ARQ Sequence number also needed in ack

Sender

timeoutretransmission Sender thinks this

is an ack for frame 1

0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13

Stop-and-wait ARQOperation with 1-bit sequence numbers in

frames and ackstimeout

Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017

Alternating-Bit ProtocolSender P1 (initial state = 1a)

1b

1a-A1 +D1

Receiver P2 (initial state = 1a)

1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit

Sender and Receiver specified by communicating finite-state machines

Notation for ed e labels

1a

2a4b

4a 2b

3

deliver data deliver data

-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit


Notation for edge labels-m send m essage m

+m receive m essage m if it iswaiting to be received

3a

3b-A0+D0

10172017

Protocol state space is infinite

14

Alternating-Bit Protocol (cont)

Assertion If Sender and Receiver communicate via lossy FIFO channels thecommunicate via lossy FIFO channels the alternating-bit protocol provides reliable in-order data delivery

Assumption A frame is retransmitted infinitely many times if it is lost infinitely many times


many times

10172017

Note A real protocol is typically designed to retransmit a fixed number of times (say k)

Stop-and-wait ARQ performance analysis

Sender 2τ + TA + TP

Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15

Average number of transmissions per frame

1

probability transmission is unsuccessfulProb[success after transmissions] for 1 2

(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P

infin infinminus= = minus

1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP

= minus = minusminus minus

= =minus

10172017

Timeout duration T gt 2τ +TA +TP

Each unsuccessful transmission usesTf + T

Each successful transmission usesTf + 2τ + TA + TP

Average time per frame(Nf ndash 1) (Tf +T) + (Tf + 2τ + TA + TP)

Max utilization (throughput) of stop-and-wait

fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ

Propagation delay versus transmission timeAssume P = 0 TA = 0 TP = 0

(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f

d i s t a n c et i d

τ =Note


p r o p a g a t i o n s p e e df r a m e l e n g t h

t r a n s m i s s i o n r a t efT =

10172017

Performance of AB protocol AB protocol works but performance degrades for

channels with large delay-bandwidth product

example 1 Gbps link 15 ms prop delay 1KByte packet

Ttransmit = 8Kbits109 bitssec= 8 microsec

U = 8 microsec

30008 microsec= 000027


Note If the sender and receiver are connected by the Internet then is the end-to-end Internet delay

the protocol limits use of available bandwidth

10172017

τ

17

Pipelined protocolsPipelining sender allows multiple ldquoin-flightrdquo yet-to-

be-acknowledged packets range of sequence numbers must be increased buffering at sender andor receiver buffering at sender andor receiver


Pipelined protocols (i) concurrent logical channels (used in ARPANET) (ii) sliding window protocol (TCP)

10172017

Sliding Window Protocol Consider an infinite array Source at the

sender and an infinite array Sink at the receiver

0 1 2 andash1 a sndash1 s

send window

acknowledged unacknowledged

Source

P1Sender

r + RW ndash 1next expected


P2Receiver

0 1 2 r

received

delivered receive window

Sinkp

RW receive window sizeSW send window size (s - a le SW)

10172017

18

Sliding Windows in ActionData unit r has just been received by P2

Receive window slides forwardP d l k h P2 sends cumulative ack with sequence number it expects to receive next (r+3)

unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017

Sliding Windows in Action P1 has just received cumulative ack with

r+3 as next expected sequence number Send window slides forward


send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19

Sliding Window protocol Functions provided

error control (reliable delivery) in-order delivery in order delivery flow and congestion control (by varying send

window size) TCP uses cumulative acks (needed for correctness)

Other kinds of acks (to improve performance)

selective nack


selective nack selective ack (TCP SACK) bit-vector representing entire state of receive

window (in addition to first sequence number of window)

10172017

Sliding Windows for Lossy FIFO Channels A small number of bits in packet header for

sequence number Necessary and sufficient condition for correct

operation SW + RW le MaxSeqNumoperation SW + RW le MaxSeqNum Necessity

P1Sender

0 1 2 andash1 a

send window


Source

RW receive window sizeSW send window size


P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20

Sliding Windows for Lossy FIFO Channels Sufficiency can only

be demonstrated by Interesting special

casesbe demonstrated by using a formal method to prove that the protocol provides reliable in-order delivery See

cases SW = RW = 1

alternating-bit protocol

SW = 7 RW = 1out-of-order arrivals

t t d


yShankar and Lam ACM TOPLAS Vol 14 No 3 July 1992

not accepted eg HDLC

SW = RW

10172017

Sliding Windows for LRD Channels

Assumption Packets have bounded lifetime L B f l h f t b Be careful how fast sequence numbers are

consumed (ie by arrival of data to be sent into network)

(send rate)times L lt MaxSeqNum TCP

32 bit s b s


32-bit sequence numbers counts bytes assumes that datagrams will be discarded by IP

if too old10172017

21

Sliding Window Protocol Performance AnalysisAssumptions

ack transmission time is negligible TA = 0 receiver processing time is negligible TP = 0 send window size is W

Go to slide 3-46

send w ndow s ze s W

WTf

Tf

2τACKWTf

Tf

2τ

time


(b) WTf lt 2τ + Tf(a) WTf gt 2τ + Tf

10172017

Performance for Error-Free ChannelsMaximum utilization

1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf

Tf + 2τWT f le 2τ +Tf


U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017

W=1 is special case of alternating-bit protocol

22

Performance Analysis for Error-Prone ChannelsDefine

Nf = Average number of transmissions per frame f g p

Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1


To determine Nf for two cases Selective repeat (optimistic performance) Go-back-N (pessimistic performance)

10172017

Performance Analysis of Error-Prone ChannelsP = probability a transmission is unsuccessful

Selective repeat (-gt upper bound on U)1

N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1


Go-back-N (-gt lower bound on U)Each lost frame requires the retransmission of N frames where 1 le N le W

10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus

With probability (1ndashP)Pi a frame requires 1+iN transmissions to succeed for i=01

Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide

Go-back-N (cont)Go to slide 3-41

Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P

+ minus + + += + = =minus minus minus

For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24

Recall (from slide 3-43)

U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP

+= minus le ++ minus +

10172017

Chapter 3 outline










control

10172017

25

TCP Overview RFCs 793 1122 1323 2018 2581

reliable in-order byte steam service no ldquomessage boundariesrdquo

connection-oriented handshaking initializes

sender receiver statebefore data exchange g

send and receive buffers

pipelined send window size

determined by TCP congestion and flow control

before data exchange point-to-point

two sender-receiver pairs bi-directional data flows in

same connection MSS maximum segment

size


controlsize less than MTU of directly

connected networksocketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment

applicationwrites data

applicationreads data

10172017

TCP segment structure


32 bits

sequence number

URG urgent data (generally not used)

ACK valid

count by bytes of data(not segments)

P1 P2Send ReceiveReceive Send

q macknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

d )

bytes rcvr willingto accept

(not segments)count in 32-bit words


applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017

Control info for both forward

and reverse data transfers

26

TCP seq rsquos and ACKsSeq

sequence number of first byte in

Host A Host B

Usert

ysegmentrsquos data

ACK seq of next byte

expected from other side

cumulative ACK

typeslsquoCrsquo

host ACKsreceipt

host ACKsreceipt oflsquoCrsquo echoes

back lsquoCrsquo


Q how receiver handles out-of-order segmentsTCP spec doesnrsquot say up

to implementor

pof echoed

lsquoCrsquo

timesimple telnet scenario

10172017

TCP Round Trip Time and TimeoutQ how to set TCP

timeout value longer than RTT

Q how to estimate RTT SampleRTT measured time from

segment transmission until ACK longer than RTT but RTT varies may be

too short or too long too short premature

timeout unnecessary

retransmissions

segment transmission until ACK receipt ignore retransmissions

SampleRTT will vary want estimated RTT ldquosmootherrdquo average several recent

measurements not just current SampleRTT


retransmissions too long slow reaction

to segment loss

current SampleRTT

10172017

27

TCP Round Trip Time and Timeout

EstimatedRTT = (1- α)EstimatedRTT + αSampleRTT

E ti ll i ht d i Exponentially weighted moving average influence of past sample decreases

exponentially fast typical value α = 0125


Example RTT estimationRTT gaiacsumassedu to fantasiaeurecomfr

350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)

SampleRTT Estimated RTT

10172017

28

Setting the timeout interval EstimtedRTT plus ldquosafety marginrdquo

large variation in EstimatedRTT -gt larger safety marginmargin

estimate how much SampleRTT deviates from EstimatedRTT and updateDevRTT = (1-β)DevRTT +

β|SampleRTT-EstimatedRTT|


TimeoutInterval = EstimatedRTT + 4DevRTT

(typically β = 025)

Then set timeout interval

10172017

Chapter 3 outline










control

10172017

29

TCP reliable data transfer

TCP creates reliable service on top of IPrsquos

Retransmissions are triggered byservice on top of IP s

unreliable service

Cumulative acks

TCP uses single i i i

triggered by timeout events duplicate acks

Initially consider simplified TCP sender


retransmission timer ignore duplicate acks ignore flow control

congestion control

10172017

Sliding Window ProtocolAt the sender a will be pointed to by SendBase and s by NextSeqNum


send window


SourceP1

Sender

P2 0 1 2 r

receivedr + RW ndash 1

Sinknext expected


Receiver0 1 2 r



10172017

30

TCP sender(simplified)

NextSeqNum = InitialSeqNumSendBase = InitialSeqNumloop (forever)

switch(event)

event data received from application above and send window has enough room

create TCP segment with sequence number NextSeqNum if (timer currently not running)

start timerpass segment to IP NextSeqNum = NextSeqNum + length(data)

event timer timeoutretransmit not-yet-acknowledged segment with

smallest sequence numberstart timer

event ACK received with ACK field value = yNote


event ACK received with ACK field value = y if (y gt SendBase)

SendBase = yif (there are currently not-yet-acknowledged segments)

start timerelse stop timer

end of loop forever

bull y gt SendBase means new data ackrsquoed

10172017

TCP retransmission scenario (1)Host A Host B

SendBase= 92

loss

tim

eout

X lost ACK scenario

restart timer for seq= 92


time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti

Cumulative ACK scenario


time

Stop timer

10172017


eout

premature timeout scenario SendBase= 92

Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer

What does Host A do here

32

Fast Retransmit Time-out period often

relatively long long delay before

If sender receives 3 duplicate ACKs for h d i long delay before

resending lost packet Detect lost segments

via duplicate ACKs Sender often sends

many segments back-to-back

the same data it supposes that segment after ACKed data was lost fast retransmit


If segment is lost there will likely be many duplicate ACKs

fast retransmitresend segment before timer expires

10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e

timeResending a segment after triple duplicate ACK without waiting for timeout

10172017

33


Fast retransmit algorithm

if (y gt SendBase) SendBase = yif (there is a not-yet-acknowledged segment)

start timer

else increment count of dup ACKs received for yif (count of dup ACKs received for y = 3)


( p y ) resend segment with sequence number y

reset timer for y

a duplicate ACK for already ACKed segment

fast retransmit

10172017

Chapter 3 outline










control

10172017

34

TCP Flow Controlreceiver explicitly informs

sender of (dynamically changing) amount of

sender wonrsquot overrunreceiverrsquos buffers by

flow control

free buffer space RcvWindow field in

TCP segment header

sender keeps amount of transmitted unACKed data less than most

ytransmitting too much

too fast


recently received RcvWindow value

buffer at receive side of a TCP connection

10172017

Chapter 3 outline










control

10172017

35

TCP Connection Management

initialize TCP variables seq s buffers flow control

info (e g RcvWindow)

Three way handshake

Step 1 client end system sends TCP SYN control segment to server - initial seq number chosen at randominfo (eg RcvWindow) chosen at random

Step 2 server end system receives SYN replies with SYNACK control segment allocates buffers specifies server-to-receiver

initial seq (chosen at

Active participant(client)

Passive participant(server)


random)

Step 3 client end system replies with ack (likely piggybacked in segment with app data)

10172017

TCP Connection Management (cont)Closing a connectionclient closes socket

client server

Step 1 client end system sends TCP FIN control message to server

Step 2 server receives FIN replies with ACK

close

close

it


Later no more data to send It closes connection sends FIN

closed

tim

ed w

ai

10172017

36

TCP Connection Management (cont)Step 3 client receives FIN

replies with ACK and enters ldquotimed waitrdquo

client server

will respond with ACK to a retransmitted FIN (due to loss of previous ACK)

Step 4 server receives ACK Its connection is closed

Step 5 client closes

close

close

itclosing


Step 5 client closes connection at the end of timed wait

Note protocol spec allows simultaneous FINs

10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37

Principles of Congestion Control

Congestion informally ldquotoo many sources sending too much informally too many sources sending too much

data too fast for network to handlerdquo different from flow control manifestations

long delays (queueing in router buffers) lost packets (buffer overflow at routers)


p ( ff f ) a top-10 problem

10172017

Causescosts of congestion scenario four senders multi-hop paths Timeout amp retransmit

λin

Q what happens as and increase at every sender

λin

i i f db ksender

finite shared output link buffers

Host A λin original dataλin original data plus

retransmitted data

positive feedback instability


Host B λout

10172017

38

Causescosts of congestion scenario

Host A λout

Cost of congestion when a packet is dropped any upstream transmission

Host B


when a packet is dropped any upstream transmission capacity used for that packet was wasted

behavior on right side of above graph called congestion collapse

10172017

Approaches towards congestion controlEnd-to-end congestion

controlli i f db k

Network-assisted congestion control

routers provide feedback no explicit feedback from network

congestion inferred from end-systemrsquos observed loss (or delay)

approach taken by TCP

routers provide feedback to end systems single bit indicating

congestion eg SNA DECbit ATM

TCPIP explicit congestion notification


congestion notification (ECN)

explicit sending rate for sender

10172017

39

Chapter 3 outline










control

10172017

TCP Congestion Control end-to-end control (no network

assistance) sender limits transmissionLastByteSent-LastByteAcked

How does sender determine CongWin

loss event = timeoutor 3 duplicate acksLastByteSent-LastByteAcked

le CongWin

Roughly the send bufferrsquos

where CongWin is in bytes

or 3 duplicate acks TCP sender reduces CongWin after a loss event

three mechanisms slow start reduce to 1 segment

ft tim t t

throughput le CongWinRTT bytessec


where CongWin is in bytesand throughput is λin in slide 3-74

after timeout event AIMD (additive increase

multiplicative decrease)

Note For now consider RcvWindow to be very large such that the send window size is equal to CongWin They are referred to as rwnd and cwnd respectively in the textbook

10172017

40

TCP Slow Start

Probing for usable bandwidth

When connection begins CongWin = 1 MSS Example MSS = 500 bytes amp RTT = 200 msec initial rate = 2500 bytessec = 20 kbps

l bl b d d h b M R


available bandwidth may be gtgt MSSRTT desirable to quickly ramp up to a higher rate

10172017

TCP Slow Start (more) When connection

begins increase rate exponentially until first loss event or

Host A

TT

Host B

first loss event or ldquothresholdrdquo double CongWin every

RTT done by incrementing CongWin by 1 MSS for every ACK received

Summary initial rate

R


Summary initial rate is slow but ramps up exponentially fast time

10172017

41

Congestion avoidance state amp responses to loss events

Q If no loss when should the exponential increase switch to linear

A When CongWin gets to 10

12

14

ow s

ize

)

TCPReno

3 dup ACKs

A When CongWin gets to current value of threshold

Implementation For initial slow start

threshold is set to a large value (eg 64 Kbytes)

0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe


Subsequently threshold is variable

At a loss event threshold is set to 12 of CongWin just before loss event

Transmission round

Tahoe Reno

Notes 1 For simplicity CongWin is in number of segments in the above graph 2 Renorsquos window inflation and deflation steps (details) omitted

10172017

Rationale for Renorsquos Fast Recovery After 3 dup ACKs

CongWin is cut in half (multiplicative decrease)

3 dup ACKs indicatenetwork capable of ( p )

window then grows linearly (additive increase)

But after timeout event CongWin is set to 1 MSS

instead window then grows

exponentially to a threshold

network capable of delivering some segments

timeout occurring before 3 dup ACKs is ldquomore alarmingrdquo


exponentially to a threshold then grows linearly

10172017

Additive Increase Multiplicative Decrease (AIMD)

42

TCP Reno (example scenario)

CongWin Timeout

halved

3 dupACKs

3-84

Initial slow start tthreshold reached during slow start

Transport Layer (SSL)

3 dupACKs during slow startbefore reaching initial threshold

10172017

Summary TCP Congestion Control (Reno) When CongWin is below Threshold sender in

slow-start phase window grows exponentially (until loss event or exceeding threshold)loss event or exceeding threshold)

When CongWin is above Threshold sender is in congestion-avoidance phase window grows linearly

When a triple duplicate ACK occurs Thresholdset to CongWin2 and CongWin set to Threshold


Threshold

When timeout occurs Threshold set to CongWin2 and CongWin is set to 1 MSS

10172017

43

AIMD in steady state (when no timeout)

multiplicative decreasecut CongWin in half after loss event (3 dup acks)

additive increaseincrease CongWin by 1 MSS every RTT in the absence of any

16 Kbytes

24 Kbytes

congestionwindow

acks)the absence of any loss event probing

What limits the average window size (or throughput)


8 Kbytes

timeLong-lived TCP connection10172017

TCP Throughput limited by loss rate TCP average throughput (approximate) of

send buffer under AIMD in terms of loss rate L 122 b t dMSSth h t times

where MSS is number of bytes per segment Example 1500-byte segments 100ms RTT

to get 10 Gbps throughput loss rate needs to be very low

bytessecondthroughputRTT L

=


to be very lowL = 210-10

New version of TCP needed for high-speed applications

10172017

44

Is TCP fairTwo competing sessions Additive increase gives slope of 1 as window size increases multiplicative decrease reduces window size to half

(proportionally)(proportionally)

W equal window size

loss decrease window by factor of 2


WConnection 1 window size

congestion avoidance additive increase

y

10172017

Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2


AIMD only provides convergence to same window size not necessarily same throughput rate

capacity R

10172017

45

No fairness in practiceUDP Some multimedia apps use

UDP instead of TCP They can tolerate packet

Parallel TCP connections nothing prevents an app

from opening parallel connections between 2 can tolerate packet

loss do not want rate

throttled by congestion control ndash send at constant rate

connections between 2 hosts Web browsers do this


Chapter 3 Summary principles behind transport

layer servicesl i l i

instantiation and implementation in the I t tmultiplexing

demultiplexing reliable data transfer connection management flow control congestion control

Next leaving the network

ldquoedgerdquo (application

Internet UDP TCP


congestion control edge (application transport layers)

into the network ldquocorerdquo

10172017

2

Transport services and protocols provide logical communication

between app processes on different hosts


different hosts transport protocol runs in

end systems (primarily) send side breaks app

messages into segments passes to network layer

rcv side reassembles segments into messages

applicationtransportnetwork


segments into messages passes to app layer

data linkphysical

10172017

Internet transport-layer protocols

unreliable unordered datagram delivery by UDP

f ll f ldquob


network no-frills extension of ldquobest-

effortrdquo IP reliable in-order byte

delivery by TCP connection setup flow control congestion control






application


congestion control services not available

delay guarantees bandwidth guarantees


physical pptransportnetworkdata linkphysical

10172017

3

Chapter 3 outline










control

10172017





application

transport

P1 application

transport

t k

application

transport

P2P3 P4P1

processthreadsocket



network

link

physical

network

link

physical

network

link

physical


4



32 bits



applicationdata

other header fields


(message)


10172017






k t ith d ti ti t




10172017

5












10172017


P1 P1P2

SP 9157 SP 9157

P3

SP 5775DP 80

D-IPCS-IP B

P4


ClientIPB

clientIP A

serverIP C

SP 9157DP 80

SP 9157DP 80

D-IPCS-IP AD-IPC

S-IP B

10172017

6

Chapter 3 outline










control

10172017







each UDP segment


32 bits

Application

length checksum



Applicationdata

(message)


7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

3

Chapter 3 outline










control

10172017





application

transport

P1 application

transport

t k

application

transport

P2P3 P4P1

processthreadsocket



network

link

physical

network

link

physical

network

link

physical


4



32 bits



applicationdata

other header fields


(message)


10172017






k t ith d ti ti t




10172017

5












10172017


P1 P1P2

SP 9157 SP 9157

P3

SP 5775DP 80

D-IPCS-IP B

P4


ClientIPB

clientIP A

serverIP C

SP 9157DP 80

SP 9157DP 80

D-IPCS-IP AD-IPC

S-IP B

10172017

6

Chapter 3 outline










control

10172017







each UDP segment


32 bits

Application

length checksum



Applicationdata

(message)


7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

4



32 bits



applicationdata

other header fields


(message)


10172017






k t ith d ti ti t




10172017

5












10172017


P1 P1P2

SP 9157 SP 9157

P3

SP 5775DP 80

D-IPCS-IP B

P4


ClientIPB

clientIP A

serverIP C

SP 9157DP 80

SP 9157DP 80

D-IPCS-IP AD-IPC

S-IP B

10172017

6

Chapter 3 outline










control

10172017







each UDP segment


32 bits

Application

length checksum



Applicationdata

(message)


7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

5












10172017


P1 P1P2

SP 9157 SP 9157

P3

SP 5775DP 80

D-IPCS-IP B

P4


ClientIPB

clientIP A

serverIP C

SP 9157DP 80

SP 9157DP 80

D-IPCS-IP AD-IPC

S-IP B

10172017

6

Chapter 3 outline










control

10172017







each UDP segment


32 bits

Application

length checksum



Applicationdata

(message)


7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

6

Chapter 3 outline










control

10172017







each UDP segment


32 bits

Application

length checksum



Applicationdata

(message)


7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

7










error recovery


10172017







detail s d h d






hellip

10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

8





1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1


1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

wraparound

sumchecksum

10172017

Chapter 3 outline











control

10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

9






10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

10




10172017



physical link




UDP protocol

10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

11



Time


Receiver ack ack

10172017



Sender

TimeError


Receiver ack

10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

12

Stop-and-wait ARQ




Sender

Time

Error



10172017


Sender



0 0 1 0Sender

Time

0 0 1 0


Receiver

Errorack ack

10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

13



Discardtimeout

Sender

Time

0 0 1 1

ACK0

ACK0


ReceiverError

10172017


1b

1a-A1 +D1


1a 1b

-D1+A1 -D0 timeout

accept data

s s i t sit



1a

2a4b

4a 2b

3


-A1 +D0

-A0+D1

4b 4a 2a 2b

3b 3a

+A0

-D1

+A1

+A0-D0

accept data

timeout

msgs in transit




3a

3b-A0+D0

10172017


14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

14





many times

10172017




Tf

Time


Receiver

TP

TA

ττ

ack

10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

15


1


(1 )i

ii

Pb i ib P Pminus

== == minus

1 (1 )ifN i b i P P


1 1

1

1

1 0

(1 )

(1 )

(1 ) (1 )

1 1

ii i

i

i

i i

i i

fN i b i P P

P i P

d dP P P PdP dPd

= =

infinminus

=

infin infin

= =

= =

= minus

= minus = minus


21 1(1 ) (1 )

1 (1 )1

1f

dP PdP P P

NP


= =minus

10172017






fT


U( ) 2

1

f

f f A P

TP T T T T T

Pτ

=+ + + + +

minus

10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

16

U congT f

T f + 2τ


(upper bound)

f

=1

1 + 2τT f

=1

1 + 2a where a =

τT f


τ =Note




10172017





U = 8 microsec

30008 microsec= 000027




10172017

τ

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

17





10172017




send window


Source

P1Sender



P2Receiver

0 1 2 r

received


Sinkp


10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

18



unacknowledged


send window

acknowledged

SourceP1

Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

r+3

10172017




send window

acknowledged

Source

P1Sender


0 1 2 r


r + RW ndash 1Sink

P2Receiver

next expected

10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

19





selective nack




10172017




P1Sender

0 1 2 andash1 a

send window


Source



P2Receiver

0 1 2

delivered

Sinknext expected

receive window

10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

20




cases SW = RW = 1



t t d




SW = RW

10172017





32 bit s b s



if too old10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

21



Go to slide 3-46


WTf

Tf

2τACKWTf

Tf

2τ

time



10172017


1 WT f gt 2τ +Tf

Define a = τTf

U =

1 WT f gt 2τ +Tf

WTf



U =

1 W gt 2a+ 1

W1+ 2a

W le 2a+ 1

10172017


22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

22



Maximum utilization

U =

1N f

W gt 2a+1

W N f

1+ 2aW le 2a+1



10172017



N f =1

1minus P

U =

1minus P W gt 2a+ 1

W(1minusP)1+ 2a

W le 2a+ 1



10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

23

(1 ) (1 ) ifN iN P P

infin

= + minus


Go-back-N (cont)

0

1

0 0

0

(1 ) (1 )

1 (1 )

11 (1 )1

i

i i

i i

i

i

P P NP P i P

dNP P PdPdNP P

dP P

=

infin infinminus

= =

infin

=

= minus + minus

= + minus

= + minus


2

111 (1 )

(1 )

11

dP P

NP PP

NPP

minus

= + minusminus

= +minus

10172017

For 22

1 2

f f

f f

WT TNT TN a

ττ

gt +

cong +cong +

11fNPN

P= +

minus

From previous slide


Case (a)

What is N

(1 2 ) 1 2 1 211 1 1f

a P P P aP aPNP P P


For 2f fWT TN W

τle + Case (b)


111 1f

N WWP P WPN

P P

=minus += + =

minus minus

10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

24


U =

1N f

W gt 2a+1

W N

1 21f

aPNP

+=minus

1 P WP+

From previous slide

Go-back-N (cont)

W N f

1+ 2aW le 2a+1

Maximum utilization

1 2 11 2

P W aP

minus gt +

11fP WPN

Pminus +=

minus


1 2(1 ) 2 1

(1 2 )(1 )

aPUW P W aa P WP


10172017

Chapter 3 outline










control

10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

25











size




TCPsend buffer

TCPreceive buffer

socketdoor

segment



10172017



32 bits

sequence number


ACK valid





FSRPAUheadlen

notused


valid



d )




applicationdata

(variable length)

commands)

Internetchecksum

(as in UDP)

10172017



26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

26



Host A Host B

Usert

ysegmentrsquos data



cumulative ACK

typeslsquoCrsquo

host ACKsreceipt


back lsquoCrsquo



to implementor

pof echoed

lsquoCrsquo


10172017






timeout unnecessary

retransmissions






to segment loss

current SampleRTT

10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

27







350

200

250

300

RTT

(mill

isec

onds

)


100

150

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106

time (seconnds)


10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

28









10172017

Chapter 3 outline










control

10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

29




unreliable service

Cumulative acks






congestion control

10172017



send window


SourceP1

Sender

P2 0 1 2 r


Sinknext expected


Receiver0 1 2 r



10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

30



switch(event)











end of loop forever


10172017


SendBase= 92

loss

tim

eout

X lost ACK scenario



time

SendBase= 100

Stop timer

10172017

seq= 92

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

31


SendBase= 92

loss

Seq

92 t

imeo

ut

X

SendBase= 120

St ti



time

Stop timer

10172017


eout


Seq=

92 t

ime

SendBase= 120

Sendbase= 100


st



time

SendBase= 120

10172017

stop timer


32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

32











10172017

Host A Host B

X

eout

for

2nd

segm

ent


tim

e


10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

33




start timer




reset timer for y


fast retransmit

10172017

Chapter 3 outline










control

10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

34




flow control


TCP segment header



too fast




10172017

Chapter 3 outline










control

10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

35




Three way handshake







random)


10172017


client server



close

close

it



closed

tim

ed w

ai

10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

36



client server




close

close

itclosing




10172017

closedti

med

wai

closed

Chapter 3 outline










control

10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

37







10172017


λin


λin

i i f db ksender



retransmitted data



Host B λout

10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

38


Host A λout


Host B




10172017


controlli i f db k











10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

39

Chapter 3 outline










control

10172017





le CongWin





ft tim t t







10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

40

TCP Slow Start



l bl b d d h b M R



10172017



Host A

TT

Host B




R



10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

41




12

14

ow s

ize

)

TCPReno

3 dup ACKs




0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Transmission round

cong

estio

n w

indo

(seg

men

ts

thresholdTCP

Tahoe




Transmission round

Tahoe Reno


10172017












10172017


42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

42


CongWin Timeout

halved

3 dupACKs

3-84




10172017






Threshold


10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

43




16 Kbytes

24 Kbytes

congestionwindow




8 Kbytes







=




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

44



W equal window size





y

10172017


Is TCP fair

TCP connection 1

bottleneckrouter

capacity R

TCP connection 2



capacity R

10172017

45















Internet UDP TCP




10172017

45















Internet UDP TCP




10172017

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