Core Issue
The H323 gateway is on a Cisco CallManager that is used to connect ISDN devices, such as ISDN fax modems. The Basic Rate Interface (BRI) ports are configured on the network side since Cisco CallManager 4.1.3 does not support network side BRI in Media Gateway Control Protocol (MGCP).
Resolution
MSN is actually Direct-Inward-Dial (DID) in Europe. DID reserves blocks of 10, 100, or 1000 numbers. This works well for Primary Rate Interface (PRI) connections, but is overkill for a BRI. This is why on a BRI, MSN is generally used. It is the same as DID except that you only get two or three individual numbers instead of a block of 10, and the numbers do not need to be contiguous.
When the router does not send the MSN to the ISDN Device, add these commands from global configuration mode in order to allow the router to send this information:
dial-peer voice xx pots
forward-digits all
For more information on ISDN BRI, refer to Provisioning the ISDN BRI Line
