LANCOM VoIP routers switch calls between different telephone networks, e.g. the ISDN network, various SIP provider networks, and the internal telephone network. These networks generally have different ranges of numbers or even completely different conventions for addressing subscribers. Whereas the traditional land-line network uses numerical characters with country code and area access codes, the world of SIP allows alphanumerical names along with domain information.
The transition between these zones must guarantee the correct translation of "telephone numbers" so that the intended subscriber can be reached.
Depending on the application at hand, both the called and the calling numbers have to be modified in such a way that a call can be returned to the original caller.
Call number translation at the transition to outside lines is primarily implemented by mapping entries in the ISDN and SIP lines and by rules in the call-routing table.
