Everyone knows that in the event of an emergency, you pick up the phone and call 911, and you get Police, Fire or Ambulance. But how does that whole system work?
Rescue 911, hosted by William Shatner was a TV show that ran from 1989-1996, and featured re-enactments of real 911 calls. For many it was their first exposure to the 911 system, when it was still new in many places.
The First 911 call was made in 1968 in Alabama. That first 911 system routed all calls to the police. The 911 system was designed for POTS, the Plain Old Telephone Network, back when everyone had land lines. Basic 911 routed the call based on the Central Office or CO it passed through with no location data. All calls that passed through a CO would be sent to a single Public Safety Answering Point, or PSAP. A PSAP is basically the 911 call center.
A Central Office is where a phone line terminates at a phone switch, which connects your call to the rest of the phone network. Its also possible to have remote CO’s which are where lines terminate, but they can only route calls to one CO to reach the rest of the network. If your out an about and see a windowless building with a phone company sign on it, odds are its a CO.
The first big update to the 911 system was to add Automatic Number Identification and Automatic Location Identification or ANI/ALI. This is a lookup that happened when the call was placed, where the phone number (ANI) was used to query a subscriber database, and then send the subscriber information with the phone call. This worked well when everyone had a landline in a fixed location. The PSAP would now know where the caller was calling from, but routing was still based on the Topology of the phone network. Each CO still only routed to a single PSAP.
Enhanced 911 uses a selective router to route calls. With E911, A call is made, and the phone number and voice go to the central office, which sends it to the selective router. the router then queries the ALI Database with the phone number to retrieve the subscriber information, then uses that to query the Master Street Address Guide, which identifies the proper PSAP to send the call to, and then routes the call there. This allows multiple PSAPs to serve an area – for example city calls get routed to the Cities PSAP, while rural ones are sent to a different PSAP. Call routing can now be done based on location, and not just Telco topology.
Cell phone providers use a Mobile Positioning Center to assign a Pseudo ANI to the call. The selective router then routes the call to the correct PSAP based on the Cell towers location. The client location can be determined by triangulation on the radio network, or in some cases the phone can send the devices geographic coordinates to the positioning center. This requires an active 911 call to be in progress. Network Triangulation works on non smart devices, and provides a general location, that is not precise.
Many traditional land lines have been replaced by VOIP Service. When using VOIP, the call is routed to a VOIP Positioning Center to get a location. In its simplest form, the VPC will provide the address of the subscriber. VPC’s can also handle dynamic entries, for example,Microsoft teams when enabled for External VOIP Calling, allows you to set your location using location services so your address dynamically updates if your device moves around with you. The VPC then routes the call to the Selective router to determine the appropriate PSAP.
Phase 2 E911 was only finally implemented across Canada in 2010. Phase 2 E911 Sends the Voice Call, and the location only to the PSAP, and is the currently the Minimum required service level in Canada. 911 is pretty dumb.
Your smart phone,watch, car and many other devices can also send Data to 911. right now these service providers send that 911 data to Emergency Data Brokers, such as RapidSOS or Interado. The broker is able to collect all the various data about an incident, and provide it to a PSAP. This includes data that your phone sends, including the voice call and location, But can include other information such as health data, which seats were occupied, and which airbags deployed in a car. This information is sent over the internet to the PSAP, This data is nice to have, but is not required by regulation, so may not be available to every PSAP, as PSAPs typically need to subscribe to the service, which is typically free for the PSAP to do. Services like RapidSOS are also how E911 PSAPs enable SMS texting to 911.
NG911 is a fully modern 911 system, and is IP Based. At the Core of the service is the Emergency Incident Data Object, which is a package of information including the voice call, and all the other data about the call. Its transmitted in one package, and enables photos and video to be included in the call. per CRTC regulation, PSAPs need to be NG911 compatible my March 31/2027, though only voice services need to be offered by that date. NG911 will open up new services, like allowing everyone to sms text 911, and allow PSAPs to forward calls to each other, so if someone in Halifax calls 911 about their friend needing help in Ottawa, the call can be forwarded on to the appropriate PSAP.
So what happens when your call reaches a PSAP?
Nova Scotia maintains 4 Primary PSAPs, depending where you are, the selective router will send you to one of these 4 Centers. If a call is not answered within a prescribed time frame, it is routed to another PSAP. The four primary PSAPs are operated by HRM, CBRM, Valley Dispatch and the RCMP, and these are locations where a call taker will answer the 911 call.
Calls for medical assistance from all 4 Primary PSAPs are transferred to EHS’s secondary PSAP, which EHS refers to as the Medical Communications Center, or MCC. At the MCC a call taker will collect information from the caller, and an in many cases provide care instructions.
When a Call taker at a PSAP takes a 911 call, they create an incident in the Computer Aided Dispatch System or CAD. The Call taker will typically confirm and clarify the location, write a short narrative of what happened, and categorize the incident. Workflows vary, but that incident then goes on to a dispatcher to manage. As part of the incident transfer, The call can be sent to other systems, which can automatically dispatch units, sending notifications to those units to respond. the dispatcher can then pass on updates from the call taker to responding units via radio. Some CAD systems will dispatch certain units in a predefined matrix based on location, or others will select the closes unit of the appropriate type.
In HRM 911 calls are answered and sent to police and fire dispatchers all within the same physical PSAP. Three other PSAPs handle calls for Nova Scotia; CBRM in Sydney who dispatch police and fire in CBRM, Valley Dispatch in Kentville, who also dispatch various fire departments around the province, and the RCMP based in Dartmouth. There are additional Fire and police dispatches that serve smaller departments throughout the province that calls for service can be sent to. For example Digby Dispatch dispatches 30 Fire Departments in South West Nova Scotia. The New Glasgow police department also has its own dispatch.
Typically the dispatcher does not talk to the 911 Caller, that is the role of the call taker. One exception to this is calls for an ambulance.
When units are responding to a call, they will typically communicate with dispatch. Since dispatch audio is recorded, this communication creates a record. Units will typically notify when they arrive, when they need something and when they clear the scene. Most units are also equipped with an MDT, or Mobile Data Terminal. The MDT runs a CAD Client and can be used to receive updates from dispatch, access additional information about an incident. The MDT can also provide mapping data, and a text messaging facility with dispatch and other units.
the province maintains two key datasets for 911 – these are Street Center lines, and civic addresses. These allow location information to be translated to a physical point on a map, and resources be dispatched there. MDT maps can also display locations of other units responding to a call, the location of resources like Fire Hydrants, or building standpipes and even building footprints themselves.