On the Properties of a Congestion Control Mechanism for Signaling Networks Based on a State Machine

Congestion control in signaling systems is a necessity to fulfil the requirements of a tele-communication network that aims satisfy the customers’ requirements on service quality. Heavy network load is an important source of customer dissatisfaction as congested net-works result in deteriorated service quality. Sessions of a signaling service with high real time demands which are subject to unacceptable delays may be obsolete or prematurely terminated by the customer; in either way, they are a burden to the signaling network. It would ease the load of the network and improve the performance of all sessions in progress, if such delayed sessions could be aborted as quickly as possible. By measuring the network delay on individual signals of a service session, it is possible to perform signaling network congestion control that considers the state in the entire signaling network. Under the assumption that a session comprises a sequence of signals between one originating node and an arbitrary number of destination nodes, it is possible to predict the total duration of a session. The prediction is calculated from previously completed signals using a state machine, which is defined per signaling link. The annihilation of sessions, for which the prediction exceeds a predefined time limit, is an embryo of a simple signaling network congestion control mechanism (CCM). This simple CCM increases the number of successfully completed services with several hundred percent under favorable circum-stances. The state machine approach is proven to perform well in all types of environ-ments. The robustness and stability of the proposed CCM is demonstrated in a wide range of environments. The fairness in the admission of signaling services into the network at very high loads are also shown to be good