H323 Redundancy between two ISR gateways

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Oct 4th, 2007
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I have 2 ISR gateways with one E1 circuit on both. In callmanager i have 1 Route list and one route group with both gateways identified. If i make outside call the call is routed to gateway 1 this is all ok. if all trunks busy on gateway 1 the call is created via gateway 2 and proceeds ok. Now the problem. If i fail the E1 on the firsat gateway i can see the initial call going to this gateway, the call is rejected due to the failure of the E1, but the call does not then try gateway 2 !! Any ideas would be helpfull. The callmanager is 5.1. I cannot use MGCP for htese gateways because i also need FAX support T38 which is not supported on MGCP with callmanager version 5.1

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Overall Rating: 5 (4 ratings)
Jaime Valencia Sun, 06/15/2008 - 09:20
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courtesy of gogasca:

H323 Failover

The default behavior in IOS, when there are no valid POTS dial-peers for a call to go out of, is to return “unallocated number” as a cause code to CCM. This can happen even if a t1 goes down. When the T1 goes down, the POTS peer is marked as down, and when CCM sends a call to the gateway, it'll return a UAN cause code to the ccm, causing CCM (by default) to stop hunting for other available gateways. There are ways to change the behavior using service parameters in CCM, but this behavior didn't make sense to me, so we looked for other ways to do it.

It turns out that you can issue the global command "no dial-peer outbound status-check pots" on the IOS GW, if you're opposed to changing the CCM behavior. What this command will do is cause the dial-peer to stay up. IOS will try and route the call, and when the T1 is down, it returns "No circuit available" to CCM. When CCM receives this cause code, it knows there's been a non-user error, and continues hunting, achieving the desired behavior.

In your case since it is H323 it will be retruning only H225 release comp message with proper code to continue re-routing.

The IOS code will translate any code we get from pots side to IP side

you may also use the search feature within netpro, probably someone already asked the same thing



if this helps, please rate


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