[This is pre-release documentation and subject to change in future releases. This topic's current status is: Milestone-Ready]

Topic Last Modified: 2010-07-09

Microsoft Communications Server 2010 uses the following components to provide E9-1-1 functionality to supported clients.

Location Information Server

The Location Information Server, installed as part of Web services, distributes the locations to the clients. The Location Information Server stores a copy of the wiremap created by the administrator in a Location database (or defined partner database). During client registration, the client queries the Location Information Server for a location based on network elements. If the client is located outside of the network, the user can be prompted to input the location of the client manually.

Location Database

The Location database contains a mapping of network information, such as a subnet, switch port, MAC address information and WIFI access points, to a location. The Location Information Server uses this information to return a location to a client when the client located within a defined network.

For more information about populating the Location database, see Configure the Location Database.

Mediation Server

Mediation Server translates signaling and, in some configurations, media between your internal Communications Server infrastructure and an Internet Protocol/Public Switched Telephone Network (IP-PSTN) gateway or a Session Initiation Protocol (SIP) trunk. To support E9-1-1, the Mediation Server routes emergency calls that include location information and a callback number, from E9-1-1 enabled Communications Server clients to the Emergency Services Provider using a SIP trunk. For more information, see Enhanced 9-1-1 (E9-1-1) and Mediation Server.

SIP Trunking

A SIP trunk is an IP connection that establishes a SIP communications link between your organization and a switching entity beyond your firewall. For more information about deploying a SIP trunk for E9-1-1, see the following topics:

Each emergency call includes a SIP INVITE. The SIP INVITE contains the PIDF_LO, originally provided to the client by the Location Information Server, and a 10 digit callback number stored in FROM. The PIDF-LO document and FROM are described below:


The Presence Information Data Format Location Object (PIDF-LO) is an XML formatted location document standardized by the Internet Engineering Task Force (IETF). The Location Information Server uses the PIDF-LO format to store locations and transmit the location to the client. The PIDF-LO location is included in the SIP INVITE as a means of conveying location from the client to the Emergency Service Provider.


FROM is included in an SIP INVITE and contains a 10 digit callback number that the PSAP can use to contact the client initiating the emergency call. For the return call, the Mediation Server needs to forward appropriate SIP headers that instruct the client to ignore call handling such as call forwarding, and team calling.

Emergency Services Provider

In order to support E9-1-1 as part of a Communications Server deployment, you must obtain E9-1-1 routing service from a certified Emergency Services Provider. The Emergency Services Provider routes emergency calls originating from Communications Server to the correct Public-safety Answer Point (PSAP) based on the location information contained within the call. The routing service provides the following benefits:

  • Clients can connect to geographically dispersed PSAPs using a single E9-1-1 trunk. If a deployment contains branch offices, a separate trunk is not required for each branch office. For more information about E9-1-1 resiliency for branch offices, and whether to use a single trunk or multiple trunks, see the “Branch Office Resiliency” section below.

  • Communications Server can provide E9-1-1 support to clients that roam to various places outside the network, such as when a user is working from home, at a hotel, or an airport. All emergency calls are patched through the same E9-1-1 connection, no matter if they are located inside or outside of the network.

When the client includes a validated address with the emergency call, the provider immediately directs the call to the PSAP. If the included address was manually entered by the user, the provider first verifies the accuracy of the location with the caller before routing the emergency call to the PSAP.