CN Presentation unit_4.pdf
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Transcript of CN Presentation unit_4.pdf
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COMPUTER NETWORKS
By
K.EUGINE RAJ
AP/SCAD Engg College
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UNIT 4
TRANSPORT LAYER
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PROCESS-TO-PROCESS
DELIVERY
The data link layer is responsible for
delivery of frames between two
neighboring nodes over a link. This iscalled node-to-node delivery.
The network layer is responsible for
delivery of datagrams between twohosts. This is called host-to-host delivery.
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Real communication takes place
between two processes .
However, at any moment, several
processes may be running on the source
host and several on the destination host.The transport layer is responsible for
process-to-process delivery-the delivery
of a packet, part of a message, from oneprocess to another.
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Types of data deliveries
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Client/Server Paradigm
Although there are several ways toachieve process-to-processcommunication, the most common one is
through the client/server paradigm. A process on the local host, called a
client, needs services from a processusually on the remote host, called a
server. Both processes (client and server) have
the same name.
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A remote computer can run several server
programs at the same time, just as localcomputers can run one or more client
programs at the same time. For
communication, we must define thefollowing:
1. Local host
2. Local process3. Remote host
4. Remote process
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Addressing
Whenever we need to deliver something toone specific destination among many, weneed an address.
At the data link layer, we need a MAC
address to choose one node among severalnodes if the connection is not point-to-point.
A frame in the data link layer needs a
destination MAC address for delivery and asource address for the next node's reply.
At the network layer, we need an IP addressto choose one host among millions.
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At the transport layer, we need atransport layer address, called a port
number, to choose among multiple
processes running on the destinationhost.
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Port numbers
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IANA Ranges
The IANA (Internet Assigned NumberAuthority) has divided the port numbers
into three ranges: well known, registered,
and dynamic (or private), as shown inFigure.
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Socket Addresses
Process-to-process delivery needs twoidentifiers, IP address and the port
number, at each end to make a
connection.The combination of an IP address and a
port number is called a socket address.
The client socket address defines theclient process uniquely just as the server
socket address defines the server
process uniquely
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Multiplexing and Demultiplexing
The addressing mechanism allows
multiplexing and demultiplexing by thetransport layer.
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Multiplexing
At the sender site, there may be several
processes that need to send packets.
This is a many-to-one relationship and
requires multiplexing.
Demultiplexing
At the receiver site, the relationship is one-
to-many and requires demultiplexing. The
transport layer receives datagrams from thenetwork layer.
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Connectionless Versus
Connection-Oriented Service
A transport layer protocol can either beconnectionless or connection-oriented.
Connectionless Service
In a connectionless service, the packets aresent from one party to another with no need
for connection establishment or connection
release. packets are not numbered; they may be
delayed or lost or may arrive out of
sequence. There is no acknowledgment either.
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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.
We will see shortly that TCP and SCTPare connection-oriented protocols.
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Reliable Versus Unreliable
The transport layer service can be reliable orunreliable.
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.
On the other hand, if the application program
needs fast service or the nature of the service
does not demand flow and error control
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