X.25 Protocol

 

       X.25 is designed to use in the WAN network. It’s compatible with most type of systems. Systems people usually call them Data Terminal Equipment (DTE) on the X.25 network can share one physical line to communicate with each other and therefore many virtual circuits will be use and existing one physical circuit. X.25 is not design for the fast networking environment, but it’s low cost since many people are sharing one physical line and it’s also reduce the waste of the bandwidth and flexible on the network resources.

 

       X.25 protocol works at Network Layer, data link layer and the physical layer of the network according to the OSI model. X.25 will also support duplex data transmission. X.25 will assemble data into packets and send through the network by the nearest path and disassemble the packets again when the packets reach to its destination.

 

       Each Data Terminal Equipment (DTE) has their unique network address on the X.25 network. When DTE need to communicate with another DTE it have to start a session for communication, therefore one side need to make a request and another DTE have to accept it or not accept. If the DTE at the other end accept the request, the data transmission will be start and session can also be closed, but it needs to be reestablished the session if the DTEs want to communicate again.

 

X.25 network uses two types of the virtual circuits, Switched Virtual Circuits and Permanent Virtual Circuits. For Switch Virtual Circuits, every time when one DTE wants to send data to another DTE, they have to establish a connection between each other on the X.25 network for temporary connection. If DTEs wants to send data frequently and consistently to each other they can use Permanent Virtual Circuits so they won’t have to establish connections when they want to communicate each time.

 

X.25 network is low cost for the companies who need to be in connect all the time, but not high speed. The cost of X.25 network will be more depend on the amount of data flow in the network. X.25 is reliable, which it has error checking technique to prevent error in the data packets by the sequence number within the data packets.