does emergency (911) dispatch uses IP ?


While reading CL network down impacting 911 services, was trying to get more information about how does this network looks like. From end user to center, I guess VOIP is used. Wondering what is the communication method from Emergency service center to end units (Police, Fire or any other services). Do they also use IP ? or its Still Radio only ? if it is IP, do they use Unicast or multicast or broadcast ?

Tried googling, but did not get much information. Any insight would be appreciated.



So, to explain the whole system……

  1. From your location to the your serving CO would be IP, POTS, Cellular however your normal phone call route.

  2. From your CO to the CO(s) serving your 911 center. Might be a dedicated trunk or may have high priority to seize channels within the normal trunking between COs. The transport being TDM or VOIP is up to the local carrier to decide.

  3. From the 911 center to the to the responders can vary by area and size. Major metros can route to dispatch centers that handle police fire and other services and they can usually communicate over a dedicated trunked radio system through the area they cover to directly communicate with responders and command elements. For a small town volunteer department the call might go to a county level dispatcher who pages out the responders. It might even be ringing a single phone at the local PD. It is up to each municipality to determine how they want the calls routed and the phone company assigns each number they assigned to a 911 center based on your street address. There is a global table (used to be maintained by Bellcore, then Telcordia, I’m not sure now) that shows ranges of street addresses mapped to the correct 911 center that is used to populate the phone system.

  4. Large Metros and advanced 911 centers send voice and packet/cellular radio to responding units often giving them maps, aerial views, known hazmat on site, and other data. If you have a large enterprise you can buy systems that allow you to communicate data like this from your organization to the 911 center. My company has a data link that sends mapping data, entrance information, and even has our security people meet the responders at the door every time 911 is called. The wrong questions is IP or radio only, they are not mutually exclusive anymore. A lot of these systems today are cellular data transmission or packet over radio. Big county wide systems are often hybrids of both. They can have their own radios covering major population density and use cellular data to fill in the shadows in their coverage. The radio user just sees the device as a walkie talkie and all that switching is transparent to them.

Steven Naslund

Chicago IL


Look for NENA (National Emergency Number Association).

20+ years ago, 911 routing required telco connections in each LATA. Some legacy (e.g. copper) still uses LATA-based 911 routing, but a lot of 911 routing (i.e. cell, voip, next-gen voice, etc) has been consolidated to a few service providers' data centers connected via IP.

NextGeneration 911 will be essentially 100% IP.

Cost, efficiency, etc.

There are multiple ways this outage can impact CL 911 service not just related to IP. Here are a few of them:

  1. You have a POTS line and you dial 911 which gets to your central office but the CO switch had no trunks out, either because they were TDM but riding one of the optical carriers or IP based. Both go down when the optical mux chokes.

  2. 911 center is probably connected to multiple COs (usually at least two) but since this outage was nationwide it is very likely that adjacent COs could have lost transmission trunks isolating the 911 center.

  3. If you are a cellular customer, that data is getting backhauled to a central office and then getting inserted into the same CO switches that lost their transmission capacity.

It is important to remember that a lot of stuff is using IP for transport but the IP network is also controlling the L1 infrastructure. In this case it looks like the IP network transmitted bad control data to the underlying fiber network.

Steven Naslund

Chicago IL

That's right. Check out

So, your town will hire someone to put the systems in the 911 center and that might be a company like West or say you are a local network provider doing VOIP you could hire west to put in a gateway for you. State and local governments can hire them to maintain the databases behind all of this. You dump all of your 911 calls to their gateway (which also has access to your customer address data) and they will handle all of the routing out of their centers for you. They also provide recording keeping an recording services if you want. Often the first choice from your site to West's datacenters is VOIP over Internet, they often then have backup landline routes and any other kind of redundancy you want to pay for. Putting in multiple datacenters and having multiple Internet feeds you can easily outperform the reliability of the traditional POTS infrastructure. This industry really took off when the CLEC/wireless industry launched to avoid creating a bunch of duplicative expensive infrastructure to meet the public safety regulations. Better to have a few giants like West take on the liability and build a nice infrastructure anyone can use than to roll you own and have to keep up with the changing technology. This kind of technology also allows smaller municipalities to get better more advanced systems by purchasing them as a service rather than a one time monster budget hit that traditional 911 centers used to be.

One more great thing about doing this is that the network becomes much more flexible and calls can be routed around failed centers or center that may themselves be in the middle of a disaster.

Disclaimer: I don't make anything from West just know of their services and roll in the industry. There are others that might be as good or better.

Steven Naslund