Session Routing

The static routing strategy described earlier only computes routes for the topology once in the course of a simulation. If the above static routing is used and the topology changes while the simulation is in progress, some sources and destinations may become temporarily unreachable from each other for a short time.

Session routing strategy is almost identical to static routing, in that it runs the Dijkstra all-pairs SPF algorithm prior to the start of the simulation, using the adjacency matrix and link costs of the links in the topology. However, it will also run the same algorithm to recompute routes in the event that the topology changes during the course of a simulation. In other words, route recomputation and recovery is done instantaneously and there will not be transient routing outage as in static routing.

Session routing provides complete and instantaneous routing changes in the presence of topology dynamics. If the topology is always connected, there is end-to-end connectivity at all times during the course of the simulation. However, the user should note that the instantaneous route recomputation of session routing does not prevent temporary violations of causality, such as packet reordering, around the instant that the topology changes.

Tom Henderson 2011-11-05