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911 Redundancy

If Customer has Critical branch Offices running SRST in single router with Centralized Call Manager in HQ, then what can be done to provide redundancy if the router goes down. For Example,

One branch has 420 IP Phones connected to Call Manager in HQ. Router is also running SRST in case if IP WAN goes down, but what happens if the router goes down. The branches can not afford to lose 911 calls due to the high volume of accidents.

What can be done to achieve redundany especially for 911 Calls?


Re: 911 Redundancy

if you are in SRST mode and then that router dies, then all the phones registered to the SRST router will now not be able to make any calls.

in your case where it is just unacceptable to lose 911 access, you'll have to get a good old fashioned analog phone and analog line.

if you could assign multiple SRST routers that would be great, but up through ccm 4.1 it is not possible. (not sure for higher versions)


Re: 911 Redundancy


Greg makes a great point regarding multiple routers. If that is not an option fo you, and you use analog lines to the router on FXO cards for SRST, the following can be done:

Configure the analog lines to ring the main desk/attendant IP phone as the attendant DN in your gateway. Configure 911 calls to use the local FXO and dial peer to the PSTN.

Jumper your analog line to a port near the front desk and another in a populated area (in addition to the FXO router connection). Place one analog phone in each area and connect it to the analog jumper feed. Label the analog phones as emergency phones, or use a red phone (ITT and Cortelco have red phones available).

When 911 is dialed from either analog or IP the call will report the same DN, the analog line's number, to the PSAP (911 operator). If the dispacther needs to call back to the facility they dial the analog line and simultaneously ring both analog phones and the IP system's attendant DN you programmed in the router/CCM for that gateway.

This assures the call from the PSAP will be answered by someone at the facility that will be able to provide information in the event an emergency occurs, whether the IP system is functioning or not.

The analog phones are also "power fail" or "emergency" phones and can be communicated to the user community as such. Remember to educate them on dialing patterns if they differ for the analog (9 or # access code).

Hope that helps a little.


Community Member

Re: 911 Redundancy

Greg and Tom,

Thanks for helping me out. I think my first option would be to use multiple SRST router, and will have to find out if CCM 4.1 supports it. If it does, then I will have to find out whether they can load balance or it would be more like Primary/Standby scenerio. Lastly, installing a multiple SRST routers would mean that I will have to purchase additional number of SRST license. For example,

Primary up and running supports 420 IP Phones/SRST.

Standby will have to be configured exactly the same way.

I will let you know when find out or anyone knows and have done it then kindly let me know.


Re: 911 Redundancy

I have never tried this but try setting this up below to see if you get redundancy. If I get a chance I will lab this out.

1. Setup device pools of remote phones to use the default gateway as a SRST reference.

2. Setup HSRP on both router. Set the HSRP preference for 1 to be higher, setup interface tracking on your PRI(never did this on a voice pri though).

3. Setup DHCP for the phones to use the HSRP as the default gateway.

4. Setup the Telephony-Service to use the HSRP IP. This I think would be the main reason why it might not work, since I'm not sure you can do this.

During failover it should pick the primary SRST router. If the PRI, FE or the router is down it should pick the secondary router.

Please rate any helpful posts.




Re: 911 Redundancy

Abbas, I'm just wondering if you had any success with this? I'm trying to propose a fault tolerant solution for a similar purpose.

Let me know what you found out.

Thanks, Lelio

Community Member

Re: 911 Redundancy


Customer has just finished the order. The implementation will not happen until late March. I will let you know. You let me know if you guys do it first.



Re: 911 Redundancy

Thanks for the update. According to these articles below, SRST & HSRP is possible. I've made an attempt to contact some of the StateStreet CIPTUG members in an effort for some pointers. Unicast me and I will try to keep you in the loop.


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