Network Layer Routing Algorithms

The routing algorithms are the part of the Network layer software that decides on which outgoing line an incoming packet should go.

• For virtual circuits the route is chosen once for each session.
• For datagrams the route is chosen once for each packet.

Desirable properties for the routing algorithms are similar to those for the whole Network layer :

In particular, robustness often distinguishes between the two main classes of routing algorithms - adaptive and non-adaptive.

Robustness is significant for two reasons :

1. Once a large network is off and running it is difficult to change the routing algorithm software, and
2. Network topologies often change - hosts, IMPs and lines frequently fail.

The better a routing algorithm can cope with changes in topology, the more robust it is.