How emergency calling works from various deployment scenarios: SfB Server

At a recent user group meeting, an attendee asked about all of the various call flows for emergency calls, from Skype for Business Server, Skype for Business Online, hybrids, and Teams. Over the next couple of posts, I’ll cover how the various scenarios work. First up, Skype for Business server.

SfB Server has native emergency calling functionality, using Location Policies, Sites, and Subnets. You can use this functionality to override the caller ID (thus setting an ELIN, or Emergency Location Identification Number), and routing it out via the appropriate gateway. You can also turn on alerting via IM, though this doesn’t do a lot of good unless you go to the next step…

SfB Server also has a Location Information Service, or LIS. This service uses the BSSID (the access point and channel a device is connected to), subnet, switch port, or switch to location the endpoint. Additionally, you can integrate with 3rd party servers/services that perform this LIS role. Some of the 3rd party services may perform better if you need to get down to the switch/switchport level to determine a location. The various locations (ERL, or Emergency Response Location) are programmed by you into the LIS, and associated with the subnet/BSSID/switch/switchport data. Yeah, this is a LOT of work to keep up! You enter the location in a format called MSAG, or Master Street Address Guide. This is a strict format that helps avoid confusion, especially when you get into suite numbers, floor numbers, and things like “east”. I have seen addresses like “235 East Highway 16 West”. It’s important to get things in the right place!

Once SfB knows your location from the LIS process, it includes the address in PIDFLO (Presence Information Data Format Location Object) in the SIP header that it sends to the gateway. There are a couple of connectivity options here:

If you have a gateway with ELIN capability (and licenses), the gateway can use the PIDFLO to select an ELIN, then send the call via the PSTN to the PSAP. If the PSAP needs to call back, the ELIN gateway maintains the translation for 30 minutes (usually configurable if 30 minutes doesn’t work for you).

If you’re in multiple PSAP jurisdictions, you’ll need to have a SIP trunk PSTN service that covers these, or if you can’t get a SIP trunk that does that, or if you’re using PRIs, you may need to route the emergency call gateway to gateway within your organization to reach the gateway that is in the correct location. You can make these routing decisions based on the ELIN (oh, 425-123-xxxx is Redmond, so send the call to that gateway, then send it to 911). You can’t route using 911 as the destination address, so this can turn into a bit of a routing mess.

An emergency call goes from a user to SfB Servers to a gateway, then via the PSTN to the PSAP

Routing emergency calls is easy when you only have one site.

If you want to avoid the routing headaches just described, you can also use 3rd party solutions from companies like West and RedSky. They have the LIS systems described above, but can also handle the ELIN translation function, and add enhanced notification/alerting options. Both offer services where your emergency calls are sent to their response centers, and then routed to the appropriate PSAP. This routing takes place automatically if the information included (think PIDFLO) is valid and matches their records. If it’s not, an operator answers the calls, gathers location information, and sends the call to the appropriate PSAP.

SfB users in two sites place calls, via the same SfB Servers, but then to different PSAPs via different gateways and PSTN services

Emergency call routing is more complex with multiple sites and/or multiple PSTN services. You MUST route emergency calls to the correct PSAP!

When you use these services, you also gain the option to have your receptionist/security desk conferenced into the call. This may be listen-only, or they may be able to speak (listen only keeps the call taker at the PSAP from getting confused as to what’s going on at the scene… Call taking is stressful. Take the stress of a help desk employee trying to decipher a technology problem over the phone, and now add the pressure of time and safety.) The conference function allows the reception/security desk personnel to take action locally – send a security or first aid team to the location, evacuate the building, meet emergency responders to direct them to the site.

Next up, we’ll hop online and see what Skype for Business Online and MS Teams can do for us, when using PSTN Calling services from Microsoft.

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