There are two VG200 Media Gateway Control Protocol (MGCP) gateways with two different Cisco IOS Software versions. One VG200 works fine, the other does not. The Cisco CallManager is 3.3.2 spH, with Public Switched Telephone Network (PSTN) connections through Foreign Exchange Station (FXS) ports on the VG200 series.
When dialing a route pattern through the non-functional VG200, the failure is dead air. Adding a number sign (#) at the end of the dialing string to eliminate interdigit timeout has no effect.
To eliminate the Cisco IOS Software version issues, the non-functional VG200 is changed to the same version of code as the functional VG200. However, this has no effect. Every route pattern fails with dead air and no feedback is given.
Cisco CallManager traces show that the route patterns do not match and are presented to the gateway. The gateway receives the MGCP packets and processes them.
This situation is caused by bad hardware, specifically a bad connection in the PSTN block. There is no problem with either VG200 in operation or configuration.
For more information about the MGCP gateway, refer to these documents: