Transport Layer By Shilpy.pptx

23.1

Chapter 23

o

_{The transport layer is responsible for the}

delivery of a message from one process to

another

o

_{The Internet model has three protocols at the}

transport layer:

UDP, TCP, and SCTP

.

• UDP: Is the simplest of the three.

• _{TCP: A complex transport layer protocol.}

• _{SCTP: The new transport layer protocol that is designed for}

specific applications such as multimedia.

Process-to-process Delivery

oThe Data link layer is responsible for delivery of frames between nodes over a link  node to node delivery

o

o

oWe need a mechanism to deliver data from one of processes running on the source host to the corresponding process running on the destination host.

23.4

The transport layer is responsible for process-to-process delivery.

6. Multiplexing and Demultiplexing –

• Multiplexing allows simultaneous use of different applications over a network which are running on a host.

• Transport layer provides this mechanism which enables us to send packet streams from various applications simultaneously over a network.

• Transport layer accepts these packets from different processes differentiated by their port numbers and passes them to network layer after adding proper headers.

Client/Server Paradigm

oProcess-to-Process communication can be achieved through client/server

oA process on the local host, known as client, needs services from a process usually on the remote host, called a server.

oBoth processes (client and server) have the same name. o For communication, we must define :

Addressing

o

At the

data link layer

, we need a

MAC addres

s

to

choose one node among several nodes

o

At the

network layer

, we need an

IP address

to

choose one host among millions.

o

At the

transport layer

, we need a

port number, to

choose among multiple processes running on the

destination host.

Port number

o A port number is a way to identify a specific process to

which an Internet or other network message is to be

forwarded when it arrives at a server.

oThe Internet uses port numbers for servers called

well-

known port numbers.

oEvery client process knows the well-known port

number of

•

_{A port number primarily aids in the transmission of data between a network}

and an application.

•

_{For example,}

_{in an incoming message/packet}

_{, the IP address is used to}

identify the destination computer/node, whereas the port number further

specifies the destination application/program in that computer.

•

_Similarly,

_{all outgoing network packets}

_{contain application port numbers in}

the packet header to enable the receiver to distinguish the specific

application.

IP addresses versus port numbers

• IP addresses and port numbers play different roles in selecting the final destination of data.

• _{The destination IP address defines the host among the different hosts}

• _{After the host has been selected, the port number defines one of the processes}

Socket Addresses

o

o _{The combination of an IP address and a port number is called a socket address.}

o A transport layer protocol needs a pair of socket addresses: the client socket address

and the server socket address.

o These four pieces of information are part of the IP header and the transport layer protocol header.

Connectionless Versus

Connection-Oriented Service

o

_{A transport layer protocol can either be connectionless or}

connection-oriented.

o

Connectionless Service

 In a connectionless service, the packets are sent from one party to another

with no need for connection establishment or connection release.

The packets are not numbered; they may be delayed or lost or may arrive out

of sequence.

_{There is no acknowledgment .}

Connectionless Versus

Connection-Oriented Service

o

_{Connection Oriented Service}

_{In a connection-oriented service, a connection is first established between the sender}

and the receiver.

_{Data are transferred.}

_{At the end, the connection is released.}

 _{TCP and SCTP (Stream Control Transmission Protocol) are connection-oriented}

Reliable Versus Unreliable

o

The transport layer service can be reliable or unreliable.

o

_{If the application layer program needs reliability, we use a reliable}

transport layer protocol by implementing flow and error control at the

transport layer. This means a slower and more complex service.

o

_{On the other hand, if the application program does not need reliability}

then an unreliable protocol can be used.

o

_{UDP is connectionless and unreliable;}

o

_{TCP and SCTP are connection oriented and reliable}

_.

o

_{These three protocols can respond to the demands of the application}