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New Member

MGCP preservation and H323

I see couple topics talking about MGCP preservation. Doesn't H323 have this? My understanding is in H323 when both CCMs go done, the call still stay. Why we have to mention this specificly in MGCP? Is this its limitation because of its slave-master native?

7 REPLIES
Bronze

Re: MGCP preservation and H323

The problem is that when the CM's come back, H.323 has now way of telling CM that it has calls active on the PRI.

So, when the CM comes back, we have to clear the calls otherwise the Telco or CM will request to use a channel that is already in use.

Bronze

Re: MGCP preservation and H323

Also, if CM goes down, the call will not stay active. Since H.225 signalling uses TCP, when the TCP session is reset or when the TCP session times out, the call will be cleared by the gateway.

New Member

Re: MGCP preservation and H323

But my understanding is that CCM only process the call, after audio path is created. CCM actually is no longer involved. So even CCM up and down doesn't matter. It seems my theory is wrong?

Blue

Re: MGCP preservation and H323

I will attempt answer annayuzhao and dugrant...

dugrant -

"The SRST/MGCP Fallback calls are H.323 calls, not MGCP calls, so if CallManager audits the endpoint, there's no active call for that MGCP endpoint. Call Preservation in its current state allows calls to be preserved when a CallManager fails and there is a backup CallManager available, but if a WAN link goes down and the gateway looses all communication with CallManager casuing it to go from MGCP to H.323 and vice versa, calls are lost"

annayuzhao -

That is true when you are talking about pots lines or T1 cas links. However, with PRI's and MGCP (H.323 is different) the Q.931 signaling is backhauled to CM. The MGCP endpoint (PRI in the gateway) does not process the Q.931 messages. So in this scenario when CM goes down all active calls will drop. There is a DDTS request to have the gateway take over the D channel and be able to generate MGCP endpoint data during any new calls such that failover and failback between CallManager and MGCP-fallback will preserve calls as well.

adignan - berbee

Bronze

Re: MGCP preservation and H323

Yes and no.

CM deals with the H.323 signalling (call setup, tear down, etc). The media is sent direclty between the endpoints.

Since H.225 (H.323 signalling layer) is TCP based, the TCP session needs to be active for the entire length of the call (so it can be torn down also).

So technically, CM is still involved in the call, but only for signalling, not media.

Blue

Re: MGCP preservation and H323

Correct. So bottom line is.... Currently with SRST/MGCP Fallback and PRI, active calls will be dropped when the WAN fails. Active calls will also be dropped when the WAN is back on line and CM is reachable. Correct? DDTS - CSCeb56616

New Member

Re: MGCP preservation and H323

Pick up this topic again.

Are the following conclusion right:

With PRI, regardless MGCP or H323,

1. When Wan lost, active call will drop.

2. When active CCM lost, active call will be preserved with the backup CCM.

So in this case, there is no difference for MGCP and H323 in terms of preservation.

Thanks

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