international switching center (ISC)

The exchanges of the national circuit-switched telephone and telecommunications networks are structured hierarchically. At the lowest level of the hierarchy are the local exch anges(OVSt), which provide the connection to the end user.

Above the local exchanges, there are the node exchanges(KVSt), the main exch anges(HVSt) and the central exch anges(ZVSt). The latter establish the connection to foreign countries via the international switching center (AVSt), which is referred to in English as the International Switching Center (ISC) or Foreign Exchange (FX).

The foreign exchange forms the transfer point to the corresponding national network. This is where the responsibility of the national providers ends. All cross-border telephone traffic is handled via the international exchange. The connections from the international exchange to the long-distance exchange(FVSt) of the corresponding country can be realized via lines, radio or also via satellite.