International Switching Center (ISC)

International Switching Center (ISC) is associated with communications switching functions like call setup, release, and routing on the international network.

For a call from country A to country B, an international call (IC) network in country A routes the connection to an international switching center (ISC). An ISC has national trunk groups to exchanges of its IC and international trunk groups to ISCs in foreign countries. The term "international network" refers to the combination of the ISCs and their interconnecting trunk groups.

Each SS7 signalling point in a network is identified by a Point Code (PC). Most signaling points have only one (national) point code. However, an international switching center is identified in the network of its country by a national PC and in the international network by an international PC.

Point codes for the international network are assigned by ITU-T and consist of parameters Z and V (3 bits) and U (8 bits). V indentifies a particular international switching center in the network, or network area specified by Z and U. In countries with one national network; up to seven ISCs can be identified.

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