SRST Inbound calls

Unanswered Question

Here's my setup:

CCM 3.3 at central location

T1's to remotes

2621's at remote sites with 2 FXO ports

SRST works as far as phones failing over, registering with 2621, and being able to dial 9 and get dial-tone from one of the FXO lines. Is it possible for CallManager to route calls to this site through PSTN when the WAN link fails? Central Site has 2 PRI circuits on a 6009 for outbound/inbound calls.

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Overall Rating: 5 (1 ratings)
dugrant Thu, 10/23/2003 - 11:45
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Yes, it is possible with 3.3, using the AAR feature (Automated Alternate Routing).

Could you elaborate a bit? I had looked into this, but Cisco's documentation on this one is a bit light. The AAR config is just an alternate prefix digit. Do I need AAR plus a set of translation patterns to get the call out to my remote PSTN line? Additionally, I can only find AAR Group settings on individual lines. Is there a way to apply this to a broader scope?

dugrant Thu, 10/23/2003 - 15:57
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I just noticed you said "when the wan link fails" I was thinking when the wan is low on bw. AAR will not work for a WAN failure. There is no automatic way to fallback to the pstn in the case of a wan failure.

The way AAR works is that if the bandwidth reservation fails, AAR is invoked and looks at the source AAR group and the destination AAR group. It sees what digits needs to be prepended, and then automatically places the call again using the new number.

You usually create 1 aar group for every physical location. Then, for each AAR group, you define what digits you need to prefix in order to reach the other AAR groups over the pstn. This is usually 9+1+area code+office code (assuming 4 digit extensions).

If your IP phones have a External Phone number mask defined on the line, then this is automatically prepended, so you may just need to prepend 9+1 for all of your locations.

trailman73 Thu, 05/27/2004 - 08:05
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SRST works perfeclty with DID nubmers at the remote branches. In the event of wan failure they can still receive and place calls. Depending on how many people are at these locations you may want to look at adding DID for them. Just a thought.


perryvdb Thu, 05/27/2004 - 07:26
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Is this also documented somewhere that you can use AAR on WAN/LAN link failures when u use on the remote sites SRST???

I want to rollout such design ,but I wanna be sure.



imranc Thu, 10/23/2003 - 16:27
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nope cuurenly AAR would not work with a WAN failure. The feature is under development and on the reoad map where you would be able to route call when the phones are gone down.




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