E911 for OCS

Sorry for sounding a bit like a advertisement but I am sure for most this is the first time they have seen a E911 solution for OCS and without stealing the thunder from the vendor who provided this solution I have kept the information fairly brief. Not much point going to deep into a technical discussion when no one actually has the solution yet. As far as I know this is the only solution for E911 for OCS currently available.

Enhanced 911 solutions in general can be complex due to alternate(fallback) routing requirements. Redundant call paths are required at every possible place a failure can occur. 911 Enable has done a great job at providing a flexible solution that has passed all early testing phases for the Enterprise Voice deployment I am working on. The diagram below is a good example of what the typical environment may look like with the solution in place.

The whole idea of the E911 (Enhanced 911) is to provide acurate location information to a PSAP. With the 911 Enable solution, this is provided through the user configurable Remote Location Management service that appears as a Tab in MOC as pictured below. Users can input their current location, which is registered to 911 Enable through their on-premise Emergency Gateway shown in the network diagram as the two red boxes.

This information is not much use without a way to match this against a user when an outbound call to 911 is generated. This matching process uses the EPID that is provided by the front-end server on every generated call and is registered by the client to the Emergency Gateway (EGW) when the client first registers to OCS along with IP address and MAC. The EPID allows the Emergency gateway to match the user against registered information in the EGW database, which is then feed back to 911 Enable to allow routing to the correct PSAP. Calls that have been identifed to have a location are routed directly to 911 Enable over an IP connection via VPN. Unconfigured clients are routed to the 911 Emergency Response Center. Without a clear location routing to the wrong PSAP is avoided.

For the solution we are trialing we have one dedicated 911 mediation server that only handles outbound 911 calls. This could of course be multiple servers in a round robin configuration for outbound call processing of 911 calls. Due to the load balancer, inbound calls are not available through this server and call rejects from the EGW servers have to be routed locally and not passed back to the mediation server for processing. This is overcome by redundant calls paths from the EGW servers that allow fallback routing to the E911 Enable Emergency Response Center through the PSTN. In my case, I have chosen to use a Cisco Unified Communications Manager as the fallback device but it could just as easily been a SIP gateway such as Audio Codes Gateway.

This type of application shows the flexibility of OCS and the agility of third party vendors. This solution was designed in a short period of time by 911 Enable and depending on your environment should be an easy solution to configure. My congratulations goes out to the folks at 911 Enable for developing this solution, as I am sure this will overcome a road block for more than one Microsoft customers looking to move to OCS Enterprise Voice.

For more information on this solution, please contact 911 Enable directly.


  1. Are you familiar with Amcom Software, they too have an enhanced E911 solution for OCS.

    John McAlpin
    E911 Product Manager
    Amcom Siftware, Inc.

  2. Hi John,

    I wasn't aware of this product.At the time I wrote this entry I believe this was the only product on the market but I am glad that other vendors are taking this on and developing more solution choices.

    Feel free to send me an email at voipnorm@live.com with your product info. I am always willing to take a look at new stuff and possibly write a review if I get the chance.


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