Define Frame Relay network. Explain and compare Frame Relay and X-25 network architecture.

Subject Computer Network
NU Year Set: 2.(b) Marks: 1+5=6 Year: 2017

Frame relay is a packet-switching telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between endpoints in wide area networks (WANs). The service, once widely available and implemented, is in the process of being discontinued by major Internet service providers. Sprint ended its frame relay service in 2007, while Verizon said it plans to phase out the service in 2015.

As we know packet switching system is a network of exchanges using high speed switches to connect multiple inputs with multiple outputs. There are three key parts to the packet switching system viz. switches, routers and TCP/IP software. 

Most of the exchanges are interlinked with other exchanges within the network. There are many possible paths through the various exchanges. Data is converted into packets suitable to the format as required for transmission medium.

There are three popular packet switching systems. They are X.25, frame relay and ATM (Asynchronous Transfer Mode).

Conventional packet switched networks use the X.25 protocols at the interfaces between all the links and switching centres. In X.25, errors are corrected by retransmission on a link by link basis. Moreover acknowledgement must always be received by a switching centre before transmission of the next packet of the message.

The above are major drawbacks of X.25 network when error rates of the links are very low. In this scenario, end to end error control between terminals is sufficient. Frame relay is designed to take care of this situation.

For the links having low error rates, frame relay has been developed. In frame relay network, each switching centre simply relays frames to be sent to the next. It does not perform error checks and does not reply any acknowledgements. This way increased throughput along with smaller delay can be achieved.

Let us see the main difference between frame Relay and X.25 packet switching below:
➤As mentioned above, in frame relay there is no link by link flow control or error control. These are considered to be responsibilities of the users' terminals. 

➤Moreover switching of logical connections are carried at layer-2 and not at layer-3. This eliminates one layer of processing and hence makes processing faster.

➤ Call control signalling is done on logical connection separate from the data. Due to this reason, intermediate nodes do not require to process call control messages on a basis of individual connections.

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