Figure 28-6: Call Flow of E9-1-1 to PSTN-Based Emergency Services Provider
1. The VoIP user dials 9-1-1.
2. The call is eventually sent to the PSTN through a PSTN Gateway.
3. The PSTN identifies the call is an emergency call and sends it to an E9-1-1 Selective
Router in the Emergency Services provider's network.
4. The E9-1-1 Selective Router determines the geographical location of the caller by
requesting this information from an Automatic Location Identification (ALI) database
based on the phone number or Automatic Number Identifier (ANI) of the 911 caller.
Exact location information is also supplied by the Master Street Address Guide
(MSAG) database, which is a companion database to the ALI database. Phone
companies and public safety agencies collaborate beforehand to create master maps
that match phone numbers, addresses and cross streets to their corresponding PSAP.
This MSAG is the official record of valid streets (with exact spelling), street number
ranges, and other address elements with which the service providers are required to
update their ALI databases.
5. The E9-1-1 Selective Router sends the call to the appropriate PSAP based on the
retrieved location information from the ALI.
6. The PSAP operator dispatches the relevant emergency services to the E9-1-1 caller.
28.11.4.2 Microsoft Lync Server 2010 and E9-1-1
Microsoft Lync Server 2010 enables Enterprise voice users to access its unified
communications platform from virtually anywhere and through many different devices. This,
together with a deployed MLTS, poses a challenge for E9-1-1 due to the difficulty in
accurately locating the E9-1-1 caller. However, Lync Server 2010 offers an innovative
solution to solving Enterprises E9-1-1 location problems.
28.11.4.2.1 Gathering Location Information of Lync 2010 Clients for 911 Calls
When a Microsoft® Lync™ 2010 client (hereafter referred to as Lync 2010 client) is
enabled for E9-1-1, the location data that is stored on the client is sent during an
emergency call. This stored location information is acquired automatically from the
Microsoft Location Information Server (LIS). The LIS stores the location of each network
element in the enterprise. Immediately after the Lync 2010 client registration process or
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