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Remote C2901 MGCP gateway won't register with CUCM

Hi, all,

We have a central call manager, we are setting up a remote office with a C2901 voice gateway that has a T1 PRI, this gateway is being configured as a H.323 gateway, everything worked fine. Now I want to get SRST working such that when WAN goes down, employees can still make outbound calls and take inbound calls. I followed SRST documentations when configuring CUCM and C2901, I would say the documentations are clear and easy to follow -- only thing is there is no adequate explanation of why those commands need to be there and I can not get SRST to work.

1), First, a basic concept question, why do we need to configure "ccm-manager fallback-mgcp"? or any MGCP related configuration on C2901? how does MGCP play the role in SRST? the router is configured as a simple voice gateway, when WAN is intact, we use H.323 protocol, when WAN goes down, we still don't need MGCP ...

2), Assuming that we needed all those SRST related MGCP configuration, I would expect C2901 to register to call manager, but I could not get this device to register as a MGCP gateway, debug mgcp packets shows:

*Sep  5 16:52:47.571: MGCP Packet sent to>
RSIP 201356931 *@voicegw-remoteoffice.local.domain MGCP 0.1
RM: restart

*Sep  5 16:52:47.631: MGCP Packet received from>
500 201356931

I verified the domain name is exactly the same as the name configured on CUCM, I tried multiple time toggling ip domain name on C2901 also, somehow CUCM does not like RSIP message from C2901, I don't have knowledge to get debug information from CUCM side of why CUCM does not like the MGCP message sent by C2901

3), When the communication is blocked from C2901 to central call manager (by using a simple ACL on C2901's default gateway device), I can still make the inbound call to an IP phone, which means, phones were correctly registered to C2901 when communication to call manager is broken, but I can not make outbound call, phones always get quick busy beeps, test call from C2901 itself (by using "csim start") is fine, which means dial-plan and ISDN/PRI is fine.


I believe we are just doing very very basic configuration and this is a common scenario, what could I do wrong?




You dont need the mgcp

You dont need the mgcp related commands if you are using H323. The commands that you need are:



service alternate default


call-manager-fallback (or) telephony-service and the relevant commands under it.

Also make sure that SRST reference has been added to the DP and the phones reset after the change made. This is what tell the phone to register to the SRST gateway when the WAN is down. The IP specified in the SRST reference should match whats configured under call-manager-fallback.

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