Analysis of the effects of SS7 message discard schemes on call completion rates during overload

The author considers the performance of a Signaling System Number 7 network when the routing processors, as opposed to transmission facilities, of signaling transfer points are overloaded. The choice of overload controls in such a situation is implementation-dependent, with an option of simply discarding messages in excess of the signaling transfer point (STP) processing capability. It is this option that is studied. Call completion performance, rather than message throughput is considered as being the primary performance measure of interest since it most accurately reflects the service provided to customers. To determine realistic call completion estimates. the authors explicitly incorporate into their analysis the effects of application-level recovery procedures and customer reattempts, both of which significantly impact the service levels achieved. In so doing, they demonstrate that message throughput can be a very misleading measure of the network´s ability to provide service. The need for some form of feedback mechanism to the traffic sources that will allow them to appropriately control traffic entering the network is demonstrated