Upgrading the Next-generation Network Part III

A softswitch is an intelligent node within a next-generation VoIP network. It makes routing decisions for both out-bond and in-bound voice calls. It determines the routing path for SIP session signaling and establishes the RTP voice streams for voice sessions. Additionally, the softswitch makes service-level decisions by determining what kind of service should be applied to a voice session.

However, most softswitch implementations are based on a TDM-switched architecture that revolves around pre-defined route and trunk concepts. From a layer 5 routing perspective, the softswitch implements a TDM routing algorithm for routing SIP. To determine the next-hop SIP node, the softswitch uses this algorithm to translate the destination number into pre-defined routes and SIP trunks. All routes and trunks must be defined and provisioned into each softswitch. Hence, from a layer 5 perspective, most initial VoIP network deployments end up looking like a (logical) mesh network, whereby each softswitch must be aware of all the other softswitches in the network, and vice versa.