SRST mode HO to Branch Site calls, Call Forward to Unity

Unanswered Question


I have a customer running CCM Cluster at HO, with SRST Branch sites, during the SRST mode in Branch sites:

1. How to configure CCM so that users from the HO will still dial 4 digits to reach SRST (Branch) users through PSTN? I can work out using Translation rule for inter site 4 digit calls from SRST site (Branch) to HO via PSTN- but not sure how to setup from HO to SRST site.

2. During SRST mode if a user is logged in using EM, any way of logging them out and can another user log in using EM?

3. If the SRST user does not have DDI, then how can he route his VM calls to HO Unity server, as his phone will not show his Extension, rather will show the Switch Board number? Also even if the user has DDI, if RDNIS is not supported by the Telco, any work around for Unity to recognize the caller based on Alternate Extensions?

Will the MWI work if RDNIS works?

4. Apart from the above, any other limitations the remote SRST users will face during a SRST operations?

many thanks

Mohamed Bari

CAE TEchnology Srvices


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Overall Rating: 4 (4 ratings)
jason-calbert_2 Wed, 05/09/2007 - 07:46
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Question 1.

Depending on what version of callmanager you are running and if you are using DID numbers you can make this work. Starting in 4.2,in 6.0 and maybe the newest 5.X there is a field called "Forward Unregistered". When the phone loses connection to callmanager it will unregister. At this point if that DN recieves a call it would be forwarded to the information in the Forward unregistered field.

For example:


Forward unregistered: 555-555-555

555-555-5555 is connected to FXO on SRST router


voice-port 0/2/2

connection plar 43917

The call would end up at DN 33917. If you have any callmanger below 4.2 you can't make this work.

Qustion 2.

If a user is in EM he will be logged out because he loses a TCP connection to callmanager. The phone will reboot and then connect to SRST thus loggin the person out of EM. Unless you are using Callmanager Express as your SRST then you can't use EM while in SRST mode.

Question 3.

In Unity you can set an alternate extension for a user. This would allow you to add any number you would like and when unity sees this number forwarded to VM then it will play the correct greeting.


Please rate helpfull post.


Thanks for the qucik response. My version would be V4.2

Q2: Are you saying when the phone looses connection to CCM and registers to SRST router, the logged in EM user will be thrown out and the Phone's native DN will be displayed? I thought who ever was logged into the Phone will retain their extension during SRST state, but cannot log out or newly log in. Please can you confirm this?

Q3: Is there any work around if some of the SRST users don't have DDI facility, then when they Call Forward to Unity, you cannot use unique number for them in Alternate Extension field?

jason-calbert_2 Wed, 05/09/2007 - 08:40
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Q2: Thinking about that you are correct the phones should retain there EM DN's when they go to SRST. This is something I will have to test in my lab as I can't find any documentation

Q3: I don't know of another workaround

Rob Huffman Wed, 05/09/2007 - 08:54
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Hi Mohamed/Jason,

Maybe this is the reference you were looking for;

Survivable Remote Site Telephony (SRST) Mode

In SRST mode, the extension mobility behavior remains the same as in previous releases. Users cannot perform login and logout operations when a phone is in SRST mode. Call processing proceeds as normal, given that the SRST gateway is configured appropriately.

From this doc;

Hope this helps!


thisisshanky Wed, 05/09/2007 - 12:00
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Simply setting alternate extension will not help for Q3. Because the forwarding station information is what Unity looks at to drop the call into the right mailbox. When a call comes into remote site and forwards ring no answer to voicemail, a second call is placed by the SRST router to the Unity pilot. This looks like a direct call to Unity, unless the forwarding station information is carried over in Redirecting IE message. If telco doesnt support this then your other option is to use FXO integration with vm-integration commands available in Cisco IOS. THis will require dtmf sequences to be setup so that the forwarding station information is passed on to Unity via the analog lines.


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