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TCP/UDP

Need of TCP and UDP ?

ntro uct on

UDP Header

Introduction TCP

TCP Header

Comparison between TCP and UDP

1OPM

TCP-UDP

Allow multiple application programs/processes execution on a host

device (having operating system) to transmit and receive datagram

independently.

Port numbers are used to distinguish different application data

.

Port number is a decimal equivalent of 16-bits

Static port number (Registered with IANA)

Dynamic port number (private or unregistered)

Using port numbers different data streams can be multiplexed and

de-multiplexed at transmitter and receiver sides respectively2OPM

TCP/UDP layering

A connection need:

IP

Port1

TCP UDP

Port2 Port1 Port2

DemuxonIP

protocol

Demuxon

Portnumber

Network

Transport

App.

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Source: (IP address, port No.) and Destination: (IP address, port No.)

Require one port (PHY connection) on host to allow multipleconnections, since each connection will have different (host, port) at otherend.

Active open: application program requests OS to connect to an(host, port).

Passive open : application program contacts OS & indicates that

it will accept incoming connection, OS assigns port and listens.

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IP: Internet Protocol

Unreliable connectionless datagram delivery service

Responsible for routing of data through intermediate networks and

computers

11 1111 1111 2222 2222 2233

4

IPheader:

1 :ICMP

6 :TCP

17:UDP

89 01 2 345 67 89 01 23 4 56 7 8 9010 12 3 4 56 7

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UDP (User Datagram Protocol)

Each UDP message contains source and destination port number,delivers message to correct recipients.

Less reliable (No ACK), delay prone, connectionless datagram

delivery.

Doesnt include acknowledge, order of messages, feedback tocontrol the rate of information flow between machines.

UDP message may be lost, duplicate or arrive out of order.

Packet can arrive faster than the recipient can process them.

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UDP Datagram format

Sourceport Destinationport

UDPmessagelen Checksum(optional)

0 8 16 3124

Data

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ource est nat on port:port num ers ent y sen ng rece v ng processes(programs or applications)

Port number & IP address allow any application in any computer on Internet to be uniquelyidentified

Used to multiplex and demultiplex datagrams to processes at a host device.

Ports can be static or dynamic

Static (< 1024 and some additional blocks, and registered port no.) assigned centrally, known as wellknown ports

Dynamic (private port no., un registered, In range from 49152 to 65535)

UDP Message length: in bytes includes the UDP header and data

Checksum: of UDP header and Data (this field is optional)OPM

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Datagram Transport

User Datagram Protocol (UDP)

A best-effort delivery, no guarantee, no ACK

Smaller overhead than TCP

Good for best-effort traffic likeperiodic updates

No long lived connection overhead on the endpoints

SNMP and DNS protocols use UDP

Data channels of some multimedia protocols, e.g., H.323 alsouses UDP due to low header processing delay

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TCP : Transmission Control Protocol

Connection-Oriented, Reliable, Bit Stream Service

Three steps to set up TCP connection between source and destination devices

1. Set up connection (Application program to program negotiation: virtual

connection setup)

2. Transfer data

3. Close connection (removing virtual connection, releasing port No.)

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Data is guaranteed to arrive, and in the correct order without

duplications

Otherwise the connection will be dropped

Imposes significant overheads

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TCP Header (followed by data/ payload)

SourcePort(16) DestinationPort(16)

SequenceNumber(32)

Acknowledgementnumber(32)

HDR

Len(4)

U

R

G

A

C

K

P

S

H

R

S

T

S

Y

N

F

I

N

WindowSize

(16)

Checksum (16) UrgentPointer(16)

Options(0ormorewords)

9

Reserved(6)

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TCP Header (cont.)

Source/destination port:port numbers identify sending & receivingprocesses (programs or applications)

Sequence Number: identifies position of packets/ segments in bit stream

Acknowledgement (piggyback) : identifies the sequence number of

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packet the sender of this packet/segment expects to receive next, refersstream flowing opposite direction

Header length (Hlen): specifies the length of the segment header in 32bit blocks/multiples. If there are no options, the Hlen = 5 (20 bytes)

Reserved for future use, set to 0

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TCP header (cont.)

Code (flags): used to determine purpose contents in header

URG: Urgent pointer field is valid

ACK: Acknowledge field is valid

PSH: This segment requests a push

RST: Reset the connection

SYN: Synchronize sequence Number

FIN: Sender has reached end of its bit/byte stream (Finish)

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TCP Header (Cont.)

Window: Advertises how much data this station is willing to

accept. It may depend on remaining buffer space also.

Checksum: Verifies the integrity of the TCP header and data. It is

mandatory.

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Urgent pointer: used with the URG flag to indicate where the

urgent data starts in the data stream. Typically used with a file

transfer abort during FTP or when pressing an interrupt key in

telnet.

Options: used for window scaling, SACK, timestamps, maximum

segment size etc.OPM

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Reliable Streams

Transmission Control Protocol (TCP)

Guarantees reliable, ordered stream of traffic

Such guarantees impose additional overhead

A fair amount of state is required on both ends

Most Internet protocols use TCP, e.g. HTTP, FTP, H.323

control channels

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Providing Reliability (TCP)

Using Acknowledgements (Ack), sender waits for positive Ack of packet sent.

In case of TIME OUT or negative Ack retransmission occurs

Flow control using WINDOW size

As per network/ channel condition Window size can be varied as per feedback from receiver

Retransmission in case of Window Transmission

Go back to N retransmission

Selective retransmission

New technique of Ack to send next expected packet instead of sending Ack of

each received packet.

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TCP : Data transfer

HostClient

Send Packet 1Start Timer Packet should arrive

ACK should be sentACK would normallyArrive at this time

Packet LostTimer

Retransmit Packet1Start Timer Receive Packet 1

Send AXK 1

Receive ACK 1Cancel Timer

Timer

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TCP flow control

Windows vary over time

Receiver advertises (in ACKs) how many it can receive

Based on buffers etc. available

Sender adjusts its window to match advertisement

If receiver buffers fill it sends smaller adverts

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Used to match buffer memory requirements of receiver

Also used to address congestion control (e.g. in intermediate

routers)

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Transport Protocols in the Internet

UDPUDPUserDatagramProtocolUserDatagramProtocol

datagramoriented

unreliable,connectionless

TCPTransmissionControlProtocol

streamoriented

reliable,connectionoriented

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unicast andmulticast

usefulonlyforfewapplications,e.g.,

multimediaapplications

usedalotforservices

networkmanagement (SNMP),

routing(RIP),naming(DNS),etc.

onlyunicast

usedformostInternetapplications:

web(http),email(smtp),file

transfer(ftp),terminal(telnet),

etc.

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