SRST plus H.323 trunk

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Jan 22nd, 2008
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I have a customer with a topology as following:

(HQ) CCM --- WAN --- (BRANCH) VoiceGW --- H.323_Gateway

Normally the branch's outgoing calls goes through the H.323 Gateway which is registered with the CallManager as a regular H.323 Gateway and it works fine.

Now we want to implement remote survivability using SRST at the branch IOS Voice Gateway. In case of a WAN failure the phones could still register with the SRST Gateway, but the question is: Could the SRST Gateway use the H.323_Gateway in order to get the calls out?

If im not wrong, in that case the Voice_GW should act as some sort of IP-IP Gateway (SCCP to H.323). Does anybody deal with this situation?

Is it supported by the SRST feature?

Any experience?

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Brandon Buffin Tue, 01/22/2008 - 08:26
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Yes, this is possible. I'm using this scenario currently with no problems. You will configure SRST using "call-manager-fallback" along with the proper commands. When the WAN is down, your phones will register to the gateway and send calls out using the dial peers that are already in place for normal H.322 functionality.

Hope this helps. If so, please rate the post.


Brandon Buffin Tue, 01/22/2008 - 08:29
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Sorry, I just reread your post and noticed that you are using 2 gateways. So, you will need the proper dial peers on each of these gateways and you will need the following commands on the H.323 gateway:

voice service voip

allow-connections h323 to h323

Hope this helps.


jhasen Tue, 01/22/2008 - 09:01
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Thanks Brandon,

However, does this feature need any special IOS option (im talking about IPIP GW feature)?

Have you prove it by yourself?

Thanks for your help in advance

Brandon Buffin Tue, 01/22/2008 - 09:54
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The commands mentioned in my previous email enable the IPIPGW functionality.


jhasen Thu, 01/24/2008 - 09:53
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Thanks Brandon but I still haven't understood very will why you need h323 to h323 calls allowed.

As far as I know when the SRST Gateway registers the phones, it uses some kinda FXS emulated virtual voice-ports (i.e. ephones) so an outgoing calls is going from a dial-peer pots towards a dial-peer

I would appreciate some light at this point, please, maybe i'm getting myself in a mess :-(

Thanks in advance

Brandon Buffin Thu, 01/24/2008 - 12:31
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You need to allow h.323 to h.323 on your h.323 gateway because the call is coming into the gateway using h.323 from your voice gateway and leaving using h.323 going out to the PSTN.


jhasen Fri, 01/25/2008 - 00:47
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Sorry, i post my last message before completing it.

I meant that when a call come from a ephone (pots dial-peer) and goes out to another h323 gateway (voip dial-peer) is the same case that when you route a call coming from a voice-port (e.g a FXS) and goes out to the Call-Manager (voip dial-peer).

Im sure youre right but im trying to understand the reason besides.

Regards and TIA

jhasen Fri, 01/25/2008 - 00:52
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Hi again, Brandon,

Maybe you misunderstood the question. The topology is as following:

(CISCO IOS SRST) --- non-cisco h.323_GW - PSTN

You I was referring to the configuration at the SRST router.

Hope this clarify the question.

Brandon Buffin Fri, 01/25/2008 - 05:21
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OK. Now I understand. That certainly makes a difference. No IPIPGW config is necessary in this case on your SRST router. Simply configure the proper dial peers pointing to the h.323 PSTN gateway.



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