Page 173 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Computer Networks/Networks

Notes Following are the steps implemented by the server machine to establish the connection:
Create a socket
Bind the socket to the port number known to all clients

Listen for the connection request
Accept connection request
Send/Receive data

Task Give a brief description of the exchange of data between a client and server machine
using transport primitives.

11.2 Elements of Transport Protocol

To establish a reliable service between two machines on a network, transport protocols are
implemented which some how resembles to the data link protocols implemented at layer 2. The
major difference lies in the fact that data link layer uses a physical channel between two routers
while the transport layer uses subnet. Following are the issues for implementing transport
protocols:

Types of Service: The transport layer also determines the type of service provided to the
users from the session layer. An error-free point-to-point communication to deliver
messages in the order in which they were transmitted is one of the key functions of the
transport layer. However, the service may be reliable or may be reliable within certain
limits or may be unreliable entirely. The order of the received message may or may not be
the same in which it was transmitted. When the connection is created between two processes,
transport layer determines the type of service to be provided to session layer at that time.
Error Control: Error detection and error recovery are the integral part of a reliable service
and therefore they are necessary to perform error control mechanism on end-to-end basis.
To control errors from lost or duplicate segments the transport layer enables unique
segment sequence numbers to the different packets of message, creating virtual circuits,
allowing only one virtual circuit per session. Timeouts mechanism is also used to remove
the packets from the network segments that have been misrouted and have remained on
the network beyond a specified time. End-to-end error control using checksums are also
used to handle any corruption in data.

Flow Control: The underlying rule of flow control is to maintain a synergy between a fast
process and a slow process. Transport layer enables a fast process to keep pace with a slow
one. Acknowledgements are sent back to manage end-to-end flow control. Go back N
algorithms is used to request retransmission of packets starting with packet number N.
Selective Repeat is used to request specific packets to be retransmitted.
Connection Establishment/Release: The transport layer creates and releases the connection
across the network. This includes naming mechanism so that a process on one machine can
indicate with whom it wishes to communicate. The transport layer enables to establish
and delete connections across the network to multiplexing several message streams onto
one communication channel.

Multiplexing/Demultiplexing: The transport layer establishes separate network connection
for each transport connection required by the session layer. To improve throughput, the
transport layer establishes multiple network connections. When the issue of throughput

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