| User | Dials | Correct call route | Correct user | Mapping, number in use | Destination line | |
|---|---|---|---|---|---|---|
| 1 | VoIP telephone | 14 | None | VoIP softphone | 14 | Internal |
| 2 | VoIP telephone | 11 | 3 # (default) | #: 11 | ISDN | |
| 3 | ISDN telephone | 14 |
|
VoIP softphone | 14 | Internal |
| 4 | VoIP telephone | 0 555 555 | 2 0# | 00241#: 0 555 555 | ISDN | |
| 5 | ISDN telephone | 0 555 555 |
|
555 555 | ISDN exchange | |
| 6 | VoIP telephone | 0 0123 666 666 | 1 00# | 0#: 0123 666 666 | SIP provider |
- Internal call between two VoIP terminal devices.
- Internal call from VoIP to ISDN. In the first pass (without the default routes) the number 11 does not match any of the routes. Similarly, no matching entry is found in the list of authenticated users. In the second pass, the default route finds # (entry 3 in the call routing table shown above) and directs the call unchanged to the ISDN line. The PBX receives the call on its internal ISDN bus, recognizes the called number as an internal MSN, and again forwards the call to the internal ISDN bus that the respective ISDN terminal device is connected to.
- Internal call from ISDN to VoIP. The ISDN PBX recognizes the destination number 14 as an internal MSN and directs the call to the corresponding internal ISDN bus. The Call Router receives the call to 14, does not find a matching entry in the call routing table but does find an entry in the list of authenticated users.
- External call from the VoIP into the local telephone network. The entry 2 in the call routing table shown above matches the dialed number. The Call Router completes the area code for the local telephone network and sends the call out to the ISDN line. Only now does the SIP PBX removes the 0 outside-line access prefix and makes the call to 0241 555 555 via the ISDN exchange line.
- External call from ISDN into the local telephone network. The ISDN PBX recognizes the destination number as an external destination, removes the 0 outside-line access prefix and completes the call to 555 555 via the ISDN exchange line.
- External call from VoIP into the national telephone network. The entry 2 in the call routing table is suitable in this case. The call router removes the 0 prefix for access to the outside line and completes the call to 0123 555 555 via the SIP line. If the SIP line is not available, then the call is made over the ISDN line. In this case, the 0 is retained in the destination number in order to gain access to an outside line through the PBX.
