Distributed QoS Routing with Bounded Flooding for Hard Real-Time Network Applications

Finding a path with suucient resources to meet the end-to-end timing constraints | which we call Quality-of-Service (QoS) routing | is indispensable to integrated services packet networks that transport time-critical traac. However, existing QoS-routing schemes based on either request-ooding or link-state dissemination are not eecient in terms of their message overhead and/or operational cost. This paper proposes a QoS-routing algorithm with bounded ooding which not only dramatically reduces message overhead and operational cost, but also performs well in nding a `qualiied' route. This signiicant overhead reduction is achieved by limiting the search area within which connection-establishment request messages are ooded. Since our scheme is based on limited request-ooding, it requires neither on-demand path calculation nor link-state dissemination, both of which are known to be very expensive. In order to limit the search area, we employ a distance table at each node storing hop counts of the shortest paths to all the nodes reachable via its outgoing links. Unlike link-state routing, the proposed scheme only needs network-connectivity information that changes much less frequently than link-load states. Extensive simulation results have demonstrated the eeectiveness of the proposed scheme in terms of performance, operational cost, and message overhead. Especially, under an ordinary operating condition in which the network's physical topology doesn't change frequently, it is shown to be much better than all the other existing QoS-routing schemes in terms of message overhead and operational cost, while providing reasonably good performance.