So lets say you have a Cisco Unified Communications Manager (CUCM) system with Unity or Unity Connection. You also have a remote site running on Callmanager Express (CME) with a SIP trunk to the CUCM as the primary gateway. To keep costs down, you decided to use your centralized unity system as the VM provider rather than purchase the Unity Express module for the router.
Here’s the problem: When you call an extension on the CME box and it rolls to voicemail, you get a fast busy.
If you do a debug, you will see the following messages:
Router# debug ccsip messages
SIP/2.0 302 Moved Temporarily
Via: SIP/2.0/UDP 192.168.1.10:5060;branch=4gsi4lsi84o57osh7j6ps
From: <sip:1000@192.168.1.10>;tag=91837ae4-cf98-d1ae-7f23-95fe870ab193-d4875345
To: <sip:5000@192.168.2.1>;tag=92FE84D7-CB6
Date: Wed, 25 Aug 2010 22:00:00 GMT
Call-ID: fe1edf80-c7519084-a9be7-5ff1bac@192.168.1.10
CSeq: 101 INVITE
Allow-Events: telephone-event
Server: Cisco-SIPGateway/IOS-12.x
Content-Length: 0
This SIP message tells the CUCM that the number has been forwarded. By default, the CUCM will not know what to do with this and so will return a reorder tone.
This is an easy problem to fix, though probably hard to describe in a few words.
You could disable this SIP feature in IOS, but that would route all voice traffic for those users (to voicemail) out to the remote site and then back to the VM server. It works if your system doesn’t support this feature… but it’s not the best solution.
Instead we can just configure CUCM to reroute calls when it receives these messages.
Start by adding a new SIP profile if you use the Standard SIP Profile.
Go to : Device -> Device Settings -> SIP Profile
Click on Find and select the Standard SIP Profile
Click the Copy button to create a copy, then give the copy a new name. Something like Custom SIP Profile or Enhanced SIP Profile is fine or use your own naming standard.
Then before you save it, check the box that says Redirect by Application… this allows the CUCM system to process redirect messages on SIP devices using this profile.
Then click Save.
Next we go configure our SIP Trunk
Device -> Trunk
Click the Find button and click on your Trunk name.
Scroll all the way down. The second to the last line is your SIP profile. Change this to the custom profile we just created.
Lastly we need to tell the trunk where to reroute calls to… look a few lines farther up and you’ll see a Rerouting Calling Search Space field. Set that to your outgoing CSS. (Or a CSS that provides access to your VM or other required services)
Save the changes and Reset the trunk.
That’s it! The CUCM system will now process the SIP redirection messages and reroute the caller accordingly.
