CALL SET-UP IN A TELECOMMUNICATIONS SYSTEM

摘要

A method of negotiating a coding type during the setting up of a voice call between two MSCs (3, 4) where the call set-up procedure is directed via an SSP (13). An Initial Address Message (IAM) is transmitted from the originating MSC (3) to the SSP (13) and includes the called number and an identification of the primary and secondary coding type preferences of the originating MSC (3). The SSP (13) determines the identity of the terminating MSC (4) based upon the called number, and further determines the coding type preferences of the terminating MSC (4). The SSP (13) then determines a call coding type preference on the basis of the coding type preferences of the terminating MSC (4) and of the coding type preference(s) of the originating exchange (3). If the call coding preference so determined differs from the primary coding type preference identified in the IAM, the primary coding type is replaced with the secondary coding type and the IAM is transmitted to the terminating MSC (4).