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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication

VII.1

25 August 2006 High-Speed Networking 7-1

Sterbenz and TouchEnd-to-End Protocols

End-to-End Protocols1. Introduction

2. Fundamentals and design principles

3. Network architecture and topology

4. Network control and signalling

5. Network components5.1 links

5.2 switches and routers

6. End systems

7. End-to-end protocols8. Networked applications

9. Future directions



End-to-End Protocols

7.1. Functions and mechanisms

7.2. State management

7.3. Framing and multiplexing

7.4. Error control

7.5. Flow & congestion control

7.6. Security & info assurance

network

application

session

transport

network

link

end system

network

link

node

network

link

nodenetwork

link

node

application

session

transport

network

link

end system


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VII.2



Ideal End-to-End Network ModelBandwidth and Delay

Zero end-to-end delay

Unlimited end-to-end bandwidth

Mapp

Mapp

D = 0

R =

ES1

CPU

ES2

CPU



End-to-End ProtocolsFunctions and Mechanisms

7.1 Functions and mechanisms

7.1.1 End-to-end semantics

7.1.2 End-to-end mechanisms

7.1.3 Transport protocols

7.1.4 Control of state

7.2 State management

7.3 Framing and multiplexing7.4 Error control

7.5 Flow and congestion control

7.6 Security and information assurance


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VII.3



E2E Functions and MechanismsEnd-to-End Semantics

Hop-by-hop functions

link layer protocols

link compression and FEC

network forwarding

link / subnet error control

embedded protocols(e.g. protocol boosters)

End-to-end functions

transport protocols

source routing

end-to-end encryption

session protocols

application protocols

Hop-by-Hop

End-to-End



E2E Functions and MechanismsEnd-to-End Argument

Hop-by-hop function composition end-to-end

Examples

HBH encryption has data in clear inside network nodes

HBH link error control doesnt cover network layer errors

End-to-End Argument T-3Functions required by communicating applications can becorrectly and completely implemented only with the knowledgeand help of the applications themselves. Providing thesefunctions as features within the network itself is not possible.


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VII.4



E2E Functions and MechanismsHop-by-Hop Performance Enhancement

E2E functions replicated HBH if performance benefit

Example

per link error control in high bandwidth--delay networksreduce E2E control loop when error

Hop-by-Hop Performance Enhancement Corollary T-3A

It is beneficial to duplicate an end-to-end function hop-by-hop ifthe result is an overall (end-to-end) improvement inperformance.



E2E Functions and MechanismsE2E Argument Misinterpretations

E2E-only

do not replicate E2E services or features HBH

violated HBH performance enhancement corollary

Everything E2E

implement as many services or feature E2E as possible

misstatement of Internet design philosophy:simple stateless network for resilience and survivability


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VII.6



E2E Functions and MechanismsTransport Protocol Service Categories

Transfer mode connectionless datagram

connection-oriented

transaction

continuous media streaming

Reliability

loss tolerance

Delivery order

ordered unordered

Traffic characteristics



E2E Functions and MechanismsTypes of Transport Protocols

Spectrum of transport protocol specialisation general purpose

functionally partitioned

application-oriented

special purpose

Software engineering and implementation choice

Transport Protocol Functionality T-IV

Transport protocols must be organised to deliver the set of end-to-end high-bandwidth, low latency services needed byapplications. Options and service models should be modularlyaccessible, without unintended performance degradation andfeature interactions.


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VII.8



E2E Functions and MechanismsControl of State

Open loop control parameters

no feedback

Closed loop initial parameters

feedback dynamic adaptation

Closed loopwith HBH feedback

Nested control loops

Open loop

parameters

data

Nested control loops

initial parameters

data

E2E feedback

receiversender

Closed loop with HBH feedback

HBH feedback

initial parameters

data

E2E feedback

Closed loop

initial parameters

data

E2E feedback

HBH loop HBH loop




Open- vs. Closed-loop Control T-6D

Use open-loop control based on knowledge of the network pathto reduce the delay in closed loop convergence. Use closed-loop control to react to dynamic network and applicationbehaviour; intermediate per hop feedback can sometimesreduce the time to converge.

Open-loop control

use when possible to eliminate control loop latency

particularly for high bandwidth--delay product networks

Closed-loop feedback control

use when necessary, e.g. reliability


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VII.9




Aggressiveness of Closed-Loop Control T-6Da

The response to closed-loop feedback must be rapid enough so

the system converges quickly to a new stable state but not soaggressive that oscillations occur due to overreaction totransients.

Aggressiveness of closed-loop control

rapid enough to system converges

not too aggressive avoid instability and oscillations



End-to-End ProtocolsState Management

7.1 Functions and mechanisms

7.2 State management

7.2.1 Impact of high speed

7.2.2 Transfer modes

7.2.3 State establishment and maintenance

7.2.4 Assumed initial conditions

7.3 Framing and multiplexing7.4 Error control

7.5 Flow and congestion control

7.6 Security and information assurance


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VII.10



State ManagementTransport and Network Connections

L4 connections

required over

connectionless L3

path with anyconnectionlesssubnetwork

may exploit

connection-oriented L3

SETUPCONNECT

network layer

end system

transport layer

connection-orientednetwork

network layer

end system

transport layer

setup-req

network layer connection

connectionlessnetwork

network layer

transport layerSETUP

CONNECT

network layer

transport layer

transport layer connection

network layer

transport layerSETUP

CONNECT

network layer

transport layer

connection-oriented

subnetwork

connectionlesssubnetwork

heterogeneous subnetworks



State ManagementImpact of High Speed

Connection shortening transmission delay decreases

signalling delay constant

E2E signalling significant fraction of time

slow high-speedfast

~1.5tRTT

~2.5tRTT ACK

RELEASEACK

RELEASE

tRTT

SETUP

RELEASE

ACK

tp

td

tp

td0

SETUP SETUP


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VII.11



State ManagementImpact of Long Latency

Connection lengthening transmission delay increases

signalling delay increases

E2E signalling open state longer

denial of resource to others

short links long links

SETUP

ACK

RELEASE

SETUP

ACK

RELEASE



Transfer ModesDatagram

Independent packets each has fully self-describing header

no network state needed to forward

tp+td


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VII.12



Transfer ModesConnection

Explicit connection setup 3-way handshake

SETUP / CONNECT / ACK

Data flow packets need connection or flow identifier

used by nodes to look up state

Release of resources and state explicit RELEASE

time out state

~tRTT

ACK

RELEASE

CONNECT

SETUP

~1.5tRTT

~tRTT

tr



Transfer ModesConnection

ConnectionStateMachine idle

establishing install state

initialising state

convergence steady state

closing release state

initialising

idle

steady-state

closing closing

establishing

CONNECTfrom net

requested

receiveSETUPfrom net

originateSETUPrequest

issueCONNECT

ACKfrom net

RELEASEfrom net

RELEASEfrom app

issueSETUP

issueRELEASE

issueRELEASE


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VII.14



Transfer ModesTransaction

Transaction request may or may not establish connection state

explicit release of connection state optional

Data returned

Overlap to reduce latency request/response with control

REQUEST

RELEASE

tr

RESPONSE

Minimise Transaction Latency T-6ACombine connection establishment with request and statetransfer to reduce end-to-end latency for transactions.



E2E State ManagementHard vs. Soft

Hard state

explicitly established and released

deterministic

delay to establish and memory to maintain

Soft state

established and removed as needed and memory allows

robust to failures

if not explicitly established, delay to accumulate

Hard vs. Soft State T-5A

Balance the determinism and stability of hard state against theadaptability and robustness to failure of soft state.


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VII.15



E2E State ManagementState Aggregation and Sharing

Sharing of state

reduces granularity ofindividual entities

state shared is fateshared state

max link ratelink characteristics

(sub)networkcharacteristics

path MTURTT estimate

perE2E path

rate/windowACKs/NAKs

global (perinterface)

pernetwork

perconnection/stream

appid1

appid2

perapplication

perapplication transfer

p

e

r

traffIc

class



E2E State ManagementState Aggregation and Sharing

Sharing of state

reduces granularity of individual entities

state shared is fate shared state

State Aggregation T-5BSpatially aggregate state to reduce complexity, but balanceagainst loss in granularity. Temporally aggregate to reduce oreliminate establishment and initialisation phase.State shared is fate shared.


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VII.17



E2E Framing and MultiplexingPacket Size and Control Overhead

Small packets large overhead short interarrival

Grouped Blocked Large

increased delay

Jumbogram

Balance Packet Size T-8A

Trade between control overhead and fine enough grainedcontrol. Choose size and aggregation methods that make senseend-to-end.

tpkt

tpkt

tgrp




Large packets

impose jitter and delay on one another

interference

in1

in2

outdelayed


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VII.18



E2E State ManagementMTU and per Hop Fragmentation

Subnetworks have limits on packet size

MTU: maximum transfer unit

If |TPDU| > min(MTU)

fragmentation will occur in the network

significant impact on packet processing rate and delay

Avoid Hop-by-Hop Fragmentation T-5F

The transport layer should be aware of or explicitly negotiatethe maximum transfer unit of the path to avoid the overhead offragmentation and reassembly.




Application Layer Framing T-8A

To the degree possible, match ADU and TPDU structure. Incases where the application can better determine structure andreact to lost and misordered ADUs, ALF should be employed.

transport layer fragmentation

ADU

MTU

TPDU

ADUADU

TPDU TPDU TPDU

TPDU

ADUADU

TPDU TPDU TPDU

ADU

application layer framing


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VII.21



E2E Error ControlTypes and Causes of Errors2

Packet duplication

retransmission

Packet insertion

undetectable header error

long packet life (two packets with same sequence number)

Fragment loss

error multiplication:fragment loss requires entire frame loss or discard



E2E Error ControlImpact of High Speed

Bandwidth--delay product increases

fixed duration error event larger relative impact

reaction to errors decreases in terms of number of bits sent

Sequence numbers

sequence numbers wrap if sequence space too small

causes packet misinsertion

Packet Control Field Values T-8COptimise header control field values to trade efficiency againstexpected future requirements. Fields that are likely to beinsufficient for future bandwidth--delay products shouldcontain a scale factor.


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VII.22



E2E Error ControlClosed Loop Retransmission: Go-Back-n

Sliding window

packets are sequentiallyacknowledged

previous ACK used for

out of sequence packet

next packet after loss

sender timer fires if ACK not received

reset transmission beginning at lost packet

significant loss penalty for high bw--delay

go back and retransmit all since loss

many unneeded retransmissions

significant additional delay

tac

A0

A1

A1

0

1

2

3

4

5

6

2

3

4

5

6

A1

A2

A3

A4

A5

A1

0

1

2

3

5

4



E2E Error ControlClosed Loop Retransmission: Go-Back-n

Fast retransmito assume several duplicate ACKs are loss

o tell sender to go-back-n

+ recovers more quickly (dont need to wait for timer to fire)

Delayed ACKo aggregate several ACKs

+ reduces ACK traffic

+ allows some receiver resequencing (within ACK aggregation)

Decouple Error, Flow, and Congestion Control T-6E

Exploit selective acknowledgements and open-loop rate controlto decouple error, flow, and congestion control mechanisms.


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VII.28



E2E Flow and Congestion ControlOpen-Loop Rate Control

network

conforming traffic

admissioncontrol

ratescheduling

ratepolicing excess traffic

receivernegotiation

Initial negotiation

admission control limits traffic to available resources

receiver negotiates what it can accept (flow control)

Steady state policingenforces traffic contract from transmitter

excess traffic may be marked and passed if capacity available



E2E Flow and Congestion ControlOpen-Loop Rate Control

Use Knowledge of Network Paths for Open-Loop T-6Do

Control Exploit open-loop rate and congestion control basedon a priori knowledge to the degree possible to reduce the needfor feedback control.

Requires connection establishment

overhead and delay for connection setup

optimistic establishment or fast reservations ameliorate

+ QOS guarantees possible in steady state

+ feedback control loops not needed during transmission

+ network stability less dependent on congestion control

unless resources significantly overbooked


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VII.29



E2E Flow and Congestion ControlOpen-Loop Rate Control: Parameters

Main parameters

peak rate rp average rate ra burstiness (peak to average ratio or max burst size)

Derived parameters jitter

rp

rabursty

uniform

time



Open Loop Rate ControlExample:7.7ATM Traffic Classes

peak rate*best effortnoneunspecified bit rateUBR

minimum rate

peak rate*dataopen loopguaranteed frame rateGFR

minimum rate

peak rate*datahybridavailable bit rateABR

peak and average rateburst

datafast reservation

open loopATM block transferABT

peak and average rateburst

dataopen loopnon-real-time

variable bit ratenrt-

VBR

peak and average rateburst, jitter, latency

dataopen loopreal-time

variable bit ratert-VBR

peak ratereal timeopen loopconstant bit rateCBR

ParametersTrafficControlNameClass

* specified in SETUP but not guaranteed


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VII.30



E2E Flow and Congestion ControlClosed-Loop Flow and Congestion Control

Use Closed-Loop Congestion Control to Adjust to T-6Dc

Network Conditions Closed-loop feedback is needed toadjust to network conditions when there are no hardreservations.

networkcongestion

control

packetscheduling

flow

control



E2E Flow and Congestion ControlClosed-Loop Flow Control

Feedback from receiver to limit rate

Window to limit amount of unacknowledged data

static window

dynamic window

combined with congestion control


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VII.31



E2E Flow and Congestion ControlCongestion Avoidance and Control

knee cliff

offered load

ideal1.0

1.0

carried

load

offered load

ideal

1.0

delay

knee

cliff

CA CC

throughput

dmin

delay

CA

CC

Congestion Avoidance T-II.4c

Congestion should be avoided before it happens. Keep queuesfrom building and operate just to the left of the knee tomaximise throughput and minimise latency.



E2E Flow and Congestion ControlClosed-Loop Congestion Control

Feedback from network to limit rate

Window to limit amount of unacknowledged data

dynamic window

conservation of packets in the network

self clocking

Required unless open loop with hard reservations

Use Closed-Loop Congestion Control to Adjust to T-6Dc

Network Conditions Closed-loop feedback is needed toadjust to network conditions when there are no hardreservations.


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VII.35



E2E Flow and Congestion ControlExample7.8 TCP Congestion Control

Fast recovery

1/2 congestion window after 3dupACK rather than slow start

Partial acknowledgement response [Hoe 1996]

1/2 window reduction only once with partial retransmit ACK

rather than per packet

RED: random early detection (discard) [Floyd 1993]

discard packets when router queue threshold exceeded

throttle TCP source earlier before congestion occurs

ECN: explicit congestion notification [Floyd 1994] use IP ECN to trigger multiplicative decrease



E2E Flow and Congestion ControlExample7.8 TCP Congestion Control

Research optimisations [jury still out]

Pacing [Visweswaraiah 1997]

spread segment transmissions

rather than burst

Rate control [Padhye 1998]

rate based on equations that describe TCP behaviour

can also make UDP transmission TCP friendly

ETEN: explicit transport error notification [Samaraweera 1997] signal loss due to channel bit errors

loss of ACK is not misconstrued as congestion


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VII.37



E2E ProtocolsExample7.9 TCP High-Speed Optimisations

TCP/IP headers

bw--delay fields that limit

sequence space

timer related

window size

Field predictability use template for

constant

predictable must compute

highly variable

payload

TCP header40B

IP header40B

payload

source port #

rcv window size

destination port

sequence number

acknowledgement number

checksum urgent pointer

total length

destination address

frag offset

source address

identifier

ver TOShl

flags

TTL header checksum

source port #

rcv window

destination port #

sequence number

acknowledgement number

checksum urgent pointer

hdr len

total length

destination address

frag offset

source address

identifier

ver TOShl

flags

TTL header checksum

UAPRSF hdr len UAPRSF

protocolprotocol

constantpredictablebw--delay sensitive



E2E ProtocolsExample7.9 TCP High-Speed Optimisations

Common optimisations [RFC 1323]

Window scale option [RFC 1323]

SYN option power-of-2 multiplier to initial window

RTTM (round-trip time measurement) [RFC 1323]

timestamp to allow RTT measurement

PAWS (protection against wrapped seq. nos.) [RFC 1323]

32-bit timestamp augments 32-bit sequence number

SACK (selective acknowledgement) [RFC 2018] byte range header options for 3 4 selective ACK ranges

Fast retransmit [RFC 2581]

retransmit on triple duplicate ACKs without waiting for timer


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