Use Cisco Unity Connection with SRST

Answered Question
Jun 25th, 2010


With SRST Router and Cisco Unity Connection installed at a remote site, if the WAN link fails, Will the IP Phone users connected to SRST router (SRST mode Active) be able to access Voice Mail from Unity connection.


Correct Answer by Jaime Valencia about 6 years 8 months ago

If you use SCCP, it's in the same location and you want VM ports to register to it.

The answer is NO.



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David Hailey Fri, 06/25/2010 - 06:41

With UC 8.0, there is also a new feature called SRSV.  It's Survivable Voicemail for remote sites.  Essentially, you have a central site where CUC is installed and the gateways there require a UMG module (Unified Messaging Gateway).  The UMG's are configured to sync database information with CUC.

In the remote sites, you would have a CUE module installed.  Each remote site CUE is defined in the UMG module (central site).  The UMG is responsible for syncing CUE with the relevant information (users, call handlers, etc).  In the event that the remote site goes into SRST, the local CUE module kicks in services and continues to provide voicemail services to the remote site users almost seamlessly.  The data from in CUE is synced from CUC (via UMG) so things like greetings are retained.  When connectivity is restored, CUE syncs with the UMG (messages received during SRSV are synced, etc) and UMG updates CUC.

For full functionality, you need not only CUCM 8.0 but also CUC 8.0.  With CUC 7x, some functionality is lost (Auto Attendant).  There are also SRSV licenses as well as CUE licensing required but I've had some customers asking about it recently so I thought I'd put it out there.


Rajesh Kalra Wed, 11/02/2016 - 17:45

Hi Rob,

I have a slightly different scenario and requirement.

At the central site I have CUCM 10.5 and CUC 10.5 cluster. The CUCM is integrated with UCCE environment. At the remote site I have contact center agents , IP Phones and voice gateway.

In the normal mode(WAN up), the contact Centre calls from PSTN to the voice gateway are sent to the UCCE environment(SIP dial-peers to CVP server).

We want to setup a basic IVR in SRST mode, such that when the callers can reach the IVR and when caller press option to reach agent, the call can route to agents as part of hunt group in SRST mode.

For playing basic IVR we have installed a new voice gateway2 with a UCS-E card (UCS-E140S-M2/K9) where we have installed CUC 10.5 for setting up call handlers to play basic IVR in SRST mode. The CUC is not to be used for voicemail purpose.

Question- you have mentioned "Integrating Cisco Unity Connection with Cisco Unified CME-as-SRST" as above.

I do not want to setup the voice gateway in CME as SRST mode, but as a normal voice gateway with SIP dial-peers pointing to the CUC on UCE-E card. So, can I setup a SIP integration between Voice gateway(in SRST mode and not CME-as-SRST)?

The objective is to pass the calls from IVR back to the phones registered in SRST mode from the CUC call handler.


csshenoy80 Fri, 06/25/2010 - 07:28


Thank you Rob and Hailey for the details shared. It is very useful information.

However, I am still looking for the case of a Site with only a SRST Router (not a CME-as-SRST or a CUE solution)

With the CME-as-SRST work for a SRST only site?

The Cisco Unity Connection document speaks about SRST sending and receiving voice messages from Cisco Unity Connection during Cisco Unified CM fallback. When the WAN is down and Connection has Basic Rate Interface (BRI) or Primary Rate Interface (PRI) access to the Cisco Unified SRST system, Connection uses ISDN signaling (attached diagram Scenario as in Cisco Documentation.JPG)

However, the query I have is what happens when the WAN link is totally down and there is NO OTHER connectivity between the cluster site and the remote SRST site (attached diagram Scenario in query.JPG)

Please suggest.

csshenoy80 Fri, 06/25/2010 - 07:42


It still makes use of the PRI/BRI between the SRST router and the CM Gateway. But I am asking for a scenario where the SRST site has a Cisco UNity connection and the WAN link is down, and there is no other connectivity between the SRST site and central CUCM cluster site.

How will the CUC ports register with the SRST router?

How will the IP Phones registered with SRST reach the Voicemail?

Will the MWI work during the Wan failure, with the IP Phones registered on the SRST?

Keith Fulcher Fri, 06/25/2010 - 07:47 you are saying that the Unity Connection is not cenralized like the CUCM

Servers, and is located at the remote site where the SRST router is located.

Is that correct?

Keith Fulcher Fri, 06/25/2010 - 08:16 that I have re read everything, you have stated the case several times.

Your Unity Connection (for whatever reason) is co located with your SRST router at a Remote site instead of being co located with the CUCM Server. Was there a reason for this? In a normal case, when you press the Voice Mail button on the phone it looks in the Phone config if it has a VM Profile configured. That VM Profile tells it to dial a certain number to reach the Unity Pilot. When you go to SRST due to a WAN outage, the SRST router will tell the Phone that the Voicemail is reachable using the number that you configured in the CallManager Fallback. The next question is if the Unity server has a reachable extension from the PSTN?

Normally you would always place the Unity Server in the same location as the CUCM servers.I have never seen a design that deviated from this rule. The reason: at your central site you should not loose Lan the Central Phones will always be able to reach the Unity. The Remote site can then dial in via PSTN when the WAN is down.

I can not think of a way for the SRST phones to reach the Unity other than the PSTN. You could play with Dial Peers and SIP trunks to the Unity, but I do not think that it will work. In theory you could set up a Dial Peer on the Gateway that "could" pass on traffic via a Sip Session Target, but you would have to test that out. You would also have to make sure your Unity License allows for this. If even possible, your config would probably look similar to the CME - Unity Cx intregration. Here is a pretty good blog that might be helpfull.

I am afraid that you are treading into untested waters.

Have Fun

PLZ Rate me if you find this helpfull.

Jaime Valencia Fri, 06/25/2010 - 09:27

I see you're asking about how the ports will register, so I'll assume you're using SCCP.

If so, Rob already provided the answer for this.


Just SRST CANNOT do this, you CANNOT register VM ports with just SRST

SRST Fallback Mode Using Cisco Unified CME

This feature enables routers to provide call-handling support for  Cisco Unified IP phones if they lose connection to remote primary,  secondary, or tertiary Cisco Unified Communications Manager  installations or if the WAN connection is down. When Cisco Unified SRST  functionality is provided by Cisco Unified CME, provisioning of phones  is automatic and most Cisco Unified CME features are available to the  phones during periods of fallback, including hunt-groups, call park and  access to Cisco Unity voice messaging services using SCCP protocol. The  benefit is that Cisco Unified Communications Manager users will gain  access to more features during fallback without any additional licensing  costs.



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csshenoy80 Fri, 06/25/2010 - 09:40

Does it mean that with only SRST ( only SRST and not CME-as-SRST), we cannot make use of the Cisco Unity Connection voice mail during the WAN outages?

David Hailey Fri, 06/25/2010 - 09:43

At this point, it's pretty clear.  No, you CANNOT use CUC installed locally with SRST.  You need CME-as-SRST to do this.



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