| 摘要 |
<p>Busy/idle status information used for the selection of circuits for carrying interexchange telephone traffic between two exchanges, is recorded in an exchange with respect to routes, circuit groups within routes and circuits within the circuit groups. A route is defined as comprising all circuits between an exchange and a single adjacent exchange and selection of a circuit for the handling of a call is done by first selecting a direct or alternate route with reference to a route busy/idle map, selecting a circuit within a selected route with reference to a circuit busy/idle map, and finally selecting a circuit within a circuit group on the basis of circuit busy/idle information. The route and circuit group status maps are self-auditing in that a route is marked busy in the route busy/idle status map if it is determined that there is not at least one circuit group which has available circuits. Similarly, a circuit group is marked busy in the circuit group status map for a route, if it is determined that there are no idle circuits in a selected circuit group. The circuit busy/idle map is maintained by updating the map each time a circuit is seized or released, by call processing programs. A source destination restriction map is used in conjunction with the route status map to avoid the selection of routes which have been restricted with respect to a particular source. A second connection status map is used in the selection of alternate routes to avoid selecting an alternate route to an intermediate exchange which lacks available facilities to the original destination exchange.</p> |
