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H323 GW calls preserved when fallback to SRST?

I've typically done MGCP GWs falling back to H323 in SRST mode and do not have any experience with call preservation when an H323 GW falls back to SRST/H323.

I would certainly think that calls would be preserved, and the phones would register to the SRST router after the call is normally terminated. However, I have a customer of a recent deployment that states otherwise. What is anyone's real-world expereince with call preservation during H323 GW fallback to SRST? Thanks much! Mike.


Re: H323 GW calls preserved when fallback to SRST?

Hi Mike,

An MGCP GW sends keepalives messages to its primary CCM every 15 secs. If CCM doesnt respond in 30 secs, the GW switches over to the NEXT configured CCM. If no CCM are reachable, the GW can fall back to using the default H323 sessions app, it its so configured.

All active analog and T1 CAS calls are maintained during the fallback transition. Callers are unaware of the fallback transition, and these active MGCP calls are cleared only when communicating callers hang up.

Active MGCP PRI and BRI backhauled calls are released during fallback, however. Any transient MGCP calls (that is, calls that are not in the connected state) are cleared when the fallback transition is triggered and must be attempted again.

All active calls are maintained except ISDN calls, which have their signalling backhauled to CCM.

In other words if you dont have a backup CCM ISDN backhauled calls will be dropped.



Super Bronze

Re: H323 GW calls preserved when fallback to SRST?


Or to put it another way... MGCP calls aren't.

H.323 calls can be:

You'd need this config and a supporing IOS:

voice service voip


call preserve



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