Trunk sparing

A telecommunications switching system handling calls with differing classes of service requirements and comprising at least one telecommunications switching centre having multiple trunk groups, each trunk group connecting to a telecommunications switching centre, each trunk group consisting of a number of trunk lines, a trunk group reserver specifying a number of trunk lines in a trunk group which should be reserved for each class of service, the number of reserved trunk lines being less than a total number of trunks available in the trunk group, and the trunk group reserver providing priorities for classes of service allowing a class to act as a super class or subclass of a different class for trunk allocation purposes;

• a trunk group allocator allocating trunks in a trunk group to calls wherein:
• if a number of trunks in a trunk group not yet allocated is greater than a total number of trunks in a trunk group reserved for differing classes of service the allocator will allocate a call to the trunk group,
• or if the number of trunks not yet allocated is less than the total number of trunks reserved for the differing classes of service and the number of trunks allocated to a class of service is less than that reserved by the class of service the allocator will allocate the call to the trunk group;
• otherwise the call will be transferred to a different trunk group or refused.

An apparatus for configuring a telecommunications trunk group switch comprising:

• a programmable switch controller connected to a telecommunications trunk group switch;
• a parameter supplier supplying parameters to the programmable switch controller;
• a program, performed by the programmable switch controller, said program:
• accepting parameters defining one or more classes of service for calls connected through the telecommunications trunk group switch,
• accepting parameters defining a maximum number of trunk group lines which may be occupied by each of the one or more classes of service resolving a number of trunk group lines which will not be allocated to any class of service,
• connecting calls to the telecommunications trunk group switch regardless of class of service up to the number of trunk group lines which are not allocated to any class of service
• thereafter connecting only calls of a class of service which has less than the maximum number of trunk group lines occupied.