Control algorithms for out-of-chain routing in a telephone network

When part of a telephone network is congested because a different traffic pattern from that designed is offered, attempts are made to improve the network throughput by utilizing other vacant facilities. One such control method is out-of-chain routing, which permits calls which overflow from the final in-chain route under the existing routing scheme (far to near rotation) to be offered to out-of-chain routes. Out-of-chain routing is expected to improve the network throughput but, on the contrary, it could degrade the network throughput by increasing the traffic toward the alternate route. Therefore a control algorithm for out-of-chain routing becomes necessary. This paper first models the switching machine which affects the network overload performance and clarifies the traffic characteristics of three-node triangle network model when out-of-chain routing is permitted unconditionally. As a result, it is clarified that the algorithm which stops routing to the out-of-chain routes with office congestion is important. Also, the algorithm which permits out-of-chain routing when there is no trunk congestion on out-of-chain routes may decrease the throughput compared with the case of no out-of-chain routing. the results presented here are confirmed by computer simulation of a laeger network.