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New Member

MGCP fallback

Acording to the IP Telephony Troubleshooting book as of IOS release 12.2(11) and MGCP gateway can be configured to be an H.323 gateway for fallback. Is there any special config that needs to be done or can I just set up a typical SRST config and let the router switch automatically?


Re: MGCP fallback

Besides configuring your dial-peers you need to configure all of you MGCP parameters and one of them is:

ccm-manager switchback {graceful | immediate | schedule-time | uptime-delay}

New Member

Re: MGCP fallback

If you have gateways (such as 2600s with NM-HDVs in them) and they are MGCP devices, I assume you NEED SRST in order to enable the gateway (in a remote office) to continue to service calls.

I'm unclear about the relationship between H.323, MGCP, and SRST.

My understanding is that normally the gateway runs MGCP with CCM.

If the CCM is unavailable, then the gateway runs in SRST and H.323 is not really in the picture since everything is internal.

Am I close?


New Member

Re: MGCP fallback

We have 2621XM routers in place with NM-2V modules that have 2FXO modules in them. They are merely acting as SRST gateways. We want to register them as MGCP gateways but we are putting 7905G phones in these locations. I just wanted to make sure that we could set them up as MGCP without any problems.

New Member

Re: MGCP fallback

Gday ,

I do beieve you will need to run CM 3.3 something to use that model of IP phone and everyone else wanting to implement a similar scenario with MGCP SRST 1760GW will need CM 3.3 as well.

Yes CM is the chief when useing MGCP GW's all you PRI ports and FXS FXO are under CM controll registered with the BOSS.

In the case of wan failure and SRST the phones will register with the router and your H.323 dial-peers will decide which ports your calls will be sent too

The phones register there directory number/s and are asigned a port and destination pattern this is your dynamic dial-plan created as the phones register .

The IP phones talk skinny protocol twith the SRST router.

These destination patterns would be matched even if you didnt use MGCP in CM mode as they are more explicit than your H.323 dial-peers (dest patt 43...)

session target ipv4:XXXXXXX

And whatever you decide to configur under call-manager-fallback will be valid when in SRST mode So you might want to create a brief translation rule that will allow users to dial the ext number of users in the remote office +moh +conference.

New Member

Re: MGCP fallback

In MGCP mode the voice gateway router acts as a stateless client, giving CallManager full control.

In H.323 mode the voice gateway router communicates with CallManager as an intelligent gateway device (it can perform call processing).

Since the purpose of SRS Telephony is to continue call processing in the event of a loss of connectivity to the CallManager(s) it follows that the voice gateway has to fail over from MGCP to H.323 mode to perform those functions. SRST is an operational feature not a protocol.

Prior versions of IOS (pre 12.2.11T, I believe) could not do this. The SRST gateway had to be configured in H.323 mode only.

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