Qualitative Link State Dissemination Control in QoS Routing

We study the behavior of a Quality of Service (QoS) routing scheme in which connection requests can be assigned to one of k alternative paths from the source to the destination. The multiple–path routing compensates for the inaccurate link state (LS) information. It is found that the frequency of LS dissemination is not the only factor to influence performance. For large LS update periods, the nature of the LS information also has a dramatic effect. For example, LS information that inhibits the use of certain links, i.e., links found to be congested when sampled in the last LS update, can block several future requests. We study the problem by considering exceptional additions to the periodic LS updates, when the residual link bandwidth decreases or increases dramatically. We subsequently examine the resulting blocking rate improvement and its corresponding control message overhead. Our findings indicate that certain schemes result consistently in blocking rate improvements for a small amount of additional con-