Connection caching to reduce signaling loads with applications to softswitch telephony
In order to support quality of service, many network operators continue to rely on connection oriented technologies, even as their networks migrate towards packet switching. Such technologies can allocate resources according to user requirements, with path stability providing low jitter for real-time services. CBR/VBR traffic classes in ATM networks fall within the connection oriented paradigm, as do Traffic Engineering initiatives such as CR-LDP and RSVP-TE protocols (from the IETF's MPLS working group). As the capacities of network links increase, network switches/ routers will need to support signaling loads that grow in proportion to these increases in bandwidth. However the capacity of such elements to process connection setup and teardown requests may not grow as quickly as transmission bandwidth. The resulting congestion in the connection control plane leads to delays in connection setup (and, in extreme cases, to setup failures). In response, next-generation switch vendors have implemented various connection-caching schemes. Despite this motivation, the problem of how to design an effective caching scheme appears to be little-studied in the literature. In this paper we propose a dynamic connection caching strategy which achieves a trade-off between bandwidth utilization and decreased signaling load. The proposed scheme is based on the optimal policy for a Markov decision process; this Markov decision process models the dynamics of caching policies on a single link. We extend the single-link approach to the network context. Simulations show that the proposed mechanism is robust and effective at reducing the signaling load without significantly decreasing throughput. The simulation scenarios feature network topologies that are appropriate for softswitch telephony, thereby demonstrating the applicability of our approach in this context.