1

Transport Protocols

Relates to Lab 5. An overview of the transport protocols of the TCP/IP protocol suite. Also, a short discussion of UDP.

2

Orientation

• We move one layer up and look at the transport layer.

ApplicationLayer

NetworkLayer

Link Layer

IP

ARPHardwareInterface

RARP

Media

ICMP IGMP

TransportLayer

TCP UDP

UserProcess

UserProcess

UserProcess

UserProcess

3

Orientation

• Transport layer protocols are end-to-end protocols • They are only implemented at the hosts

Application

Transport

Network

HOST

Data Link Data Link Data Link

Network

Application

Transport

Network

HOST

Data Link

4

Transport Protocols in the Internet

UDP - User Datagram ProtocolUDP - User Datagram Protocol• datagram oriented• unreliable, connectionless• simple• unicast and multicast• useful only for few applications,

e.g., multimedia applications• used a lot for services

– network management (SNMP), routing (RIP), naming (DNS), etc.

TCP - Transmission Control Protocol

• stream oriented• reliable, connection-oriented• complex• only unicast• used for most Internet

applications:– web (http), email (smtp), file

transfer (ftp), terminal (telnet), etc.

• The two major transport protocols of the Internet are

5

UDP Format

IP header UDP header UDP data

UDP message length Checksum

DATA

20 bytes 8 bytes

0 15 16 31

Source Port Number Destination Port Number

• Port numbers identify sending and receiving applications (processes). Maximum port number is 216-1= 65,535

• Message Length is at least 8 bytes (I.e., Data field can be empty) and at most 65,535

• Checksum is for header (of UDP and some of the IP header fields)

6

Format of TCP segments

IP header TCP header TCP data

Sequence number (32 bits)

DATA

20 bytes 20 bytes

0 15 16 31

Source Port Number Destination Port Number

Acknowledgement number (32 bits)

window sizeheaderlength

0 Flags

Options (if any)

TCP checksum urgent pointer

20 bytes

• TCP segments have a min. 20 byte header with ≥ 0 bytes of data.

7

Port Numbers

• UDP (and TCP) use port numbers to identify applications• A globally unique address for applications consists of

<IP address, type of protocol, port number>• 65,535 ports per protocol

IP

TCP UDP

UserProcess

Demultiplex

based on

Protocol field in IP

header

UserProcess

UserProcess

UserProcess

UserProcess

UserProcess

Demultiplex

based on

port number

8

UDP - User Datagram Protocol

• UDP is supports unreliable transmissions of datagrams• UDP merely extends the host-to-to-host delivery service of IP datagram to an application-

to-application service• The only thing that UDP adds to IP datagrams is multiplexing and demultiplexing (by

adding port numbers)

UDP

IP IPIP IP IP

UDP

Applications Applications

9

New Transport Protocols

• New Transport Protocols were added:– DCCP (2006): Datagram Congestion Control Protocol– SCTP (2000): Stream Control Transmission Protocol

ApplicationLayer

NetworkLayer

Link Layer

IP

ARPHardware Interface

RARP

Media

ICMP IGMP

TransportLayer

TCP UDP

User Process

User Process

User Process

User Process

DCCP SCTP

10

DCCP and SCTP

SCTP SCTP

“TCP for datagrams”

• connection-oriented (full duplex)

• more delivery options than TCP

• Message-oriented – preserves message boundaries

• Supports multiple flows (“streams” per connection)

• unreliable or reliable

• ordered or partially ordered

• congestion control

• support for multi-homing

• Used for signaling in telephone networks

DCCP

“UDP with congestion control”

“TCP without reliable byte stream”

• connection-oriented

• message-oriented

• unreliable

• unordered

• congestion control

• Intended for applications that transfer large volumes of data

• Provide more service than UDP, but less than TCP

11

SCTP Format

IP headerSCTP

headerSCTP data

Verification tag

20 bytes 12 bytes

0 15 16 31

Source Port Destination Port

Checksum

LengthType Flags

DataChunk 1

LengthType Flags

DataChunk N

...

• Many different chunk types– Data chunks– Control chunks

• Each chunk has a type-dependent header

12

DCCP Format

IP headerDCCP header

DCCP data

DATA

20 bytes12 or 16

bytes 0 15 16 31

Source Port Number Destination Port Number

Sequence number0 0

Options (if any)

type X

Data offset CCVal CsCov Checksum