From a previously question on the same answered by gogasca:
The default behavior in IOS, when there are no valid POTS dial-peers for a call to go out of, is to return âunallocated numberâ 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
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...