What are the advantages and disadvantages of X25 protocols?

Answer 1

X.25 is a connection-oriented protocol (or datagram over the WAN) designed for use in either of two types of circuits: switched or permanent.

· A Switched Virtual Circuit (SVC) is a circuit connection that you would expect with an on-demand type of service. The SVC is like a telephone call where one site requests a temporary connection to another site.

· A Permanent Virtual Circuit (PVC) is much like connecting a hotline between two sites. The hotline stays operational and can be used at anytime. These circuit types still require permanent access to the telephone company, which entails a monthly access charge.

Comparing frame relay with X.25, both protocols are based upon the principle of packet switching technology. In the engineering for each protocol, a focus was made in the area of data-type applications, not so much with voice and real-time video.

Advantages:

1. X.25 is a protocol designed for data transfer over public telephone lines. It was first developed in the 1960s to support host-to-host data transfer over noisy lines.

2. To provide redress for the problems with noisy transmission, X.25 performs extensive error checking and error recovery.

3. In a switching network, X.25 checks packets from each switch. Packets are only forwarded when a positive acknowledgment is received. Thus the X.25 protocol achieves high reliability at the expense of low data transfer speed.

Disadvantages:

1. The disadvantages of X.25 become apparent when we look at how it differs from frame relay.

2. The area of error checking shows the main differences with the two protocols. As mentioned earlier, X.25 provides error correction and retransmission functions.

3. The link layer peer protocol specified in X.25 is called LAP-B (Link Access Procedure-Balanced).

4. The LAP-B provides link management, error control, flow control and failure recovery. These operations take place in the Data Link and Network layers.

5. A high level of guarantee is given to the originator that the data is received with no errors and in the correct sequence.