Topic Last Modified: 2012-09-29

Using a SIP trunk to connect to a qualified E9-1-1 service provider is one way that you can deploy E9-1-1. For details about using an ELIN gateway to connect to a public switched telephone network (PSTN)-based E9-1-1 service provider, see Routing E9-1-1 Calls by Using an ELIN Gateway.

The following diagram shows how an emergency call is routed from Lync Server to the Public Safety Answering Point (PSAP) when you use a SIP trunk and qualified E9-1-1 service provider.

Routing E9-1-1 calls through a SIP trunk

Emergency Call Routing from Lync Server to PSAP

When an emergency call is placed from a compatible Lync Server client:

  1. A SIP INVITE that contains the location, the caller's callback number, and the (optional) Notification URL and conference callback number is routed to Lync Server.

  2. Lync Server matches the emergency number and routes the call (based on the PSTN Usage value that is defined in the applicable location policy) to a Mediation Server, and from there, over a SIP trunk to the E9-1-1 service provider.

  3. The E9-1-1 service provider routes the emergency call to the correct PSAP based on the location that is provided with the call. When the client includes a validated Emergency Response Location (ERL) with the emergency call, the provider automatically routes the call to the appropriate PSAP. If the location was manually entered by the user, the Emergency Call Response Center (ECRC) first verbally verifies the accuracy of the location with the caller before routing the emergency call to the PSAP.

  4. If you configured the location policy for notifications, one or more of your organization’s security officers are sent a special Lync emergency notification instant message. This message always pops up on the security officers’ screen(s) and contains the caller’s name, phone number, time, and location, enabling security personnel to quickly respond to the emergency caller by using an instant message or voice.

  5. If you configured the location policy for conferencing and it is supported by the E9-1-1 service provider, an internal Security Desk is conferenced into the call with either one-way audio or two-way audio.

  6. If the call is broken prematurely, the PSAP uses the callback number to contact the caller directly.