So far, we have looked at the impact of long-term associations on the applications themselves. The other layer in which they are important is the Network Layer. It is here that routing takes place, and in a complex network many routing decisions have to be taken in order to establish a path to the final destination. If the Network Layer service is CO then it is common to make use of the long-term associations in the way the networks operate. For example, a path across the networks is established when the connection is set up and remembered for its duration.
All packets belonging to the connection then follow the same path.
This means that the routing decisions have only to be made once and all the resources the connection needs at the intervening nodes can be reserved in advance. With CL operation routing decisions have to be made for each packet and there is a danger that too many packets will be routed via a particular node thus causing 'congestion'. However, in some circumstances the fact that every packet is routed individually is considered a virtue as this enables packets to be routed round failed nodes. This is undoubtedly true and the sort of applications which currently run above the VC service provided by X.25 networks exploit the inherent reliability of the service. The applications may not want that much reliability.