SRST with CME 4.0

Unanswered Question
Apr 21st, 2008

I was going through 6.x SRND, and noticed that Cisco recommends CUCME at remote locations instead of SRST since CME can provide more features than SRST if WAN goes down, and users at remote locations can not reach Centralized Call Manager Cluster.

CME, is a key system and provides a Call Processing capability locally and maintains a separate Dial Plan that works as a separte entity, but can interconnect with Call Manager via ICT or Trunk link, The two sides have their own PBXs, one with Call Manager Cluster, and the other one with CUCME (IOS based Call Manager).

Is SRND suggesting that users at remote locations can can have a primary connection via Centralized CAll Manager 6.1 at Head Quarters, and if the link to HQ goes down then the CUCME can be activated at remote locations to provide backup functionality same as SRST, but of course with more features.

I have this problem too.
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Sushil Kumar Katre Mon, 04/21/2008 - 23:30

Hi Abbas,

Earlier, SRST feature was not available on the CME router, but now Cisco have deployed thi snew fature called CME in SRST mode on CME router.

This means that you have a Central UCM and CME at remote locations. All the IP Phones registered to the central UCM. Now in case WAN link fails the users can fall back to the CME router configured as CME in SRST fallback mode.

Point to note that CME in SRST mode does not supports unity express, i.e. when the router is in SRST mode [WAN link fails], Unity Express users won't be able to se the services.

Similarly there is a draback of old SRST router. It does not supports Meet-Me Conferences during fallback.

You need to make sure what features you need during the fallback and then make appropriate selection.

NOTE - I have seen Unity Express working with CME in SRST mode, however SRST says it's not supported.

>> Sushil

rob.huffman Tue, 04/22/2008 - 04:37

Hi Abbas,

Hope all is well :) Just to add a note to the great info from Matthew and Sushil;

These are called "Cisco Unified SRST" or **"Cisco Unified CME in SRST Fallback Mode"

Cisco Survivable Remote Site Telephony 4.0 Ordering Guide

Applications and Migration to Cisco Unified SRST

Customers who initially deploy or purchase a Cisco Unified CallManager Express (CME) solution, the CME Feature License includes a provision to use the feature license for Cisco Unified Survivable Remote Site Telephony (SRST) mode without an additional charge or re-licensing to Cisco. Customers only need to re-configure the router for Cisco Unified SRST mode.

For Cisco Unified SRST Configuration Documentation, please refer to:

SRST Fallback

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.

Comparison of Cisco Unified SRST and

Cisco Unified CME in SRST Fallback Mode

Cisco Unified CME in SRST Fallback Mode

• First supported with Cisco Unified CME 4.0: Cisco IOS Software 12.4(9)T

• IP phones re-home to Cisco Unified CME if Cisco Unified Communications Manager fails. CME in SRST allows IP phones to access some advanced Cisco Unified CME telephony features not supported in traditional SRST

• Support for up to 240 phones

• No support for Cisco VG248 48-Port Analog Phone Gateway registration during fallback

• Lack of support for alias command

• Support for Cisco Unity® unified messaging at remote sites (Distributed Exchange or Domino)

• Support for features such as Pickup Groups, Hunt Groups, Basic Automatic Call Distributor (BACD), Call Park, softkey templates, and paging

• Support for Cisco IP Communicator 2.0 with Cisco Unified Video Advantage 2.0 on same computer

• No support for secure voice in SRST mode

• More complex configuration required

• Support for digital signal processor (DSP)-based hardware conferencing

• E-911 support with per-phone emergency response location (ERL) assignment for IP phones (Cisco Unified CME 4.1 only)

Cisco Unified SRST

• Supported since Cisco Unified SRST 2.0 with Cisco IOS Software 12.2(8)T5

• IP phones re-home to SRST router if Cisco Unified Communications Manager fails. SRST allows IP phones to have basic telephony features

• Support for up to 720 phones

• Support for Cisco VG248 registration during fallback

• Support for alias command

• Lack of support for features such as Pickup Groups, Hunt Groups, Call Park, and BACD

• No support for Cisco IP Communicator 2.0 with Cisco Unified Video Advantage 2.0

• Support for secure voice during SRST fallback

• Simple, one-time configuration for SRST fallback service

• No per-phone emergency response location (ERL) assignment for SCCP Phones (E911 is a new feature supported in SRST 4.1)

Hope this helps!


matthewpage Tue, 04/22/2008 - 04:53

Hi Rob

Two things;

1. Does CME 4.2/4.3 support fail back to SRTP as i believe it is supported in standard cme mode along with secure conferencing.

2. Is CUE supported in SRST and CME/SRST?



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