Overview of E9-1-1
Topic Last Modified: 2012-06-08
Microsoft Lync Server 2010 supports Enhanced 9-1-1 (E9-1-1) calling from Lync 2010 clients and Lync 2010 Phone Edition devices. When you configure Lync Server for E9-1-1, emergency calls placed from Lync 2010 or Lync 2010 Phone Edition include Emergency Response Location (ERL) information from the Location Information service database. ERLs consist of civic (that is, street) addresses and other information that helps to identify a more precise location in office buildings and other multitenant facilities. When a user makes an emergency call, Lync Server routes the call audio, along with the location and callback information, through a Mediation Server to an E9-1-1 service provider. The E9-1-1 service provider uses the civic address of the caller to route the call to the Public Safety Answering Point (PSAP) that serves the caller's location, and sends along an Emergency Service Query Key (ESQK) that the PSAP uses to look up the caller's ERL.
Lync Server 2010 supports two methods for routing emergency calls to an E9-1-1 service provider:
A Session Initiation Protocol (SIP) trunk connection to a qualified E9-1-1 service provider
An Emergency Location Identification Number (ELIN) gateway to a public switched telephone (PSTN)-based E9-1-1 service provider
When you use a SIP trunk E9-1-1 service provider, you add ERLs to the Location Information service database, and then validate the locations against a Master Street Address Guide (MSAG) that is maintained by the E9-1-1 service provider. If an E9-1-1 service provider receives a call that doesn’t have location information or has a location that has not been validated against the MSAG, the E9-1-1 service provider routes the call to a national Emergency Call Response Center (ECRC), which is staffed with specially trained personnel who verbally obtain the caller’s location, if possible, and manually route the call to the appropriate PSAP. (Some SIP trunk E9-1-1 service providers also provide customers with a PSTN direct inward dialing (DID) number to the ECRC, which provides an alternate means of routing 9-1-1 calls, if the SIP trunk fails for any reason.)
Unlike time division multiplexing (TDM) and IP-based private branch exchange (PBX) phones, which have fixed locations, a Lync 2010 endpoint can be very mobile. When you deploy the E9-1-1 feature, Lync Server 2010 helps to ensure that no matter where a caller is located, the emergency call can be routed to the PSAP that serves the caller’s location. For example, if a user’s main office is located in Redmond, Washington, but the user places an emergency call from a computer in a branch office in Wichita, Kansas, the SIP trunk or PSTN-based E9-1-1 service provider will route the call to the PSAP in Wichita, not to the PSAP in Redmond.
When you use an ELIN gateway, you also add ERLs to the Location Information service database, but you include an ELIN number for each location. The ELIN number becomes the emergency calling number during the emergency call. You must then make sure that your PSTN carrier uploads the ELINs to the Automatic Location Identification (ALI) database.
Lync-connected analog devices cannot receive location information from the Location Information service or transmit location to the E9-1-1 service provider. If you use the SIP trunk E9-1-1 service provider option and need to support E9-1-1 from analog phones, you have two options:
Traditional PS-ALI option If you have local PSTN gateways at each site where analog phones are deployed and each analog phone has a DID, you can provision the analog device’s location directly with a Private Switch/Automatic Location Identification (PS-ALI) service provider. In this case, you configure specially-crafted Lync voice policies and assign them to the analog device contact objects so that E9-1-1 calls from those phones route directly through the local gateway to the PSTN provider that services the site (instead of routing the call to an E9-1-1 service provider SIP trunk). When an emergency call is placed, a database at a PS-ALI provider that is associated with the PSTN trunk maps the DID of each analog phone to a physical location and provides this location to the PSAP. These records must be updated with the PS-ALI service provider every time phones are moved to different ERLs.
E9-1-1 service provider option You can register the analog phone DIDs and their corresponding ERLs with the E9-1-1 service provider, if this is supported by the E9-1-1 service provider. If the provider receives a call from Lync Server that doesn’t include PIDF-LO data, the provider can see if there is a database match on the calling party’s DID number. By using the ERL retrieved from its database, the provider can automatically route the emergency call to the correct PSAP, and the PSAP will receive the DID of the analog device and an ESQK record that allows the dispatcher to lookup the caller’s location.
From a Lync Server perspective, the E9-1-1 process can be separated into two stages:
Stage 1: Acquiring a location
Stage 2: Routing the emergency call to an E9-1-1 service provider
This section describes how these stages work.
If you plan to configure your infrastructure to automatically detect client location, you need to decide first which network elements you will use to map callers to locations. For details about the possible options, see Defining the Network Elements Used to Determine Location.