Core Issue
Cisco IOS Software based voice gateway runs Media Gateway Control Protocol (MGCP) for VoIP signaling control between the gateway and Cisco CallManager. External callers hear a period of secondary dial tone for inwards calls, specifically Public Switched Telephone Network (PSTN) towards Cisco CallManager. After this burst of dial tone, the call proceeds as expected: the IP phone rings and the external caller hears an in-band ringback.
This is the configuration for the customer's voice gateway router:
!
controller T1 1/0
framing esf
linecode b8zs
ds0-group 1 timeslots 1-24 type e&m-wink-start dtmf dnis
!
!
dial-peer voice 11 pots
application mgcpapp
port 3/0:1
!
Resolution
To resolve this issue, perform these steps:
- Change the voice gateway router configuration by removing the keywords dtmf dnis for the ds0-group T1 controller command.
The new configuration would be as follows:
!
controller T1 1/0
framing esf
linecode b8zs
ds0-group 1 timeslots 1-24 type e&m-wink-start
!
- After the config changes have been made, re-register the gateway to the Cisco CallManager by issuing the no mgcp | mgcp config command.