The Routing Strategies

If the process at site A wants to communicate with a process at site B, how is the message sent? If there is only one physical path from A to B (such as in a star or tree-structured network), the message must be sent through that path. Although, if there are multiple physical paths from A to B, then several routing options exist. Every site has a routing table indicating the alternative paths that can be used to send a message to other sites. A table may include information about the speed and cost of the various communication paths, and it may be updated as necessary, either manually or via programs that exchange routing information. These are some most common routing schemes are fixed routing, virtual routing, and dynamic routing.

(1)Fixed-routing :-

Where the path from A to B is specified in advance and does not change unless a hardware failure disables it. Generally, the shortest path is chosen, so that communication costs are minimized.

(2)Virtual-routing :-

The path from A to B is fixed for the duration of one session. While the different sessions involving messages from A to B may use different paths. The session could be as short as a file transfer or as long as a remote-login period.

(3)Dynamic-routing :-

When the path will be used to send a message from site A to site B is chosen only when a message is sent. Although the decision is made dynamically, separate messages may be assigned different paths. Site A will make a decision to send the message to site C; C, in turn, will decide to send it to site D, and so on. Therefore, the site will deliver the message to B. Generally, a site sends a message to another site on whatever link is the least used at that particular time.