Much of the power of the Microsoft Unified Communications platform is that it is based on SIP. This protocol enables centralization of phone resources or dial tone. SIP uses local number portability to port the local numbers to a SIP Trunk provider that routes calls that are destined to various destinations. This means users who have a 913 area code can use the same server as users who have a 303 area code. This enables the organization to centralize the dial tone. One of the great benefits of Unified Communications is that users can take their phones wherever they go. But how does a user get to the correct emergency services provider based on the user's physical location? This article explains how Enhanced 9-1-1 (E9-1-1) works in Microsoft Lync Server 2010 communications software.
Author: Robert Burnett
Publication date: January 2011
Product version: Lync Server 2010
The addition of E9-1-1 to Microsoft Lync Server 2010 communications software helps provide a secure reliable mechanism for calling emergency services. Microsoft Office Communications Server always had basic 9-1-1 capabilities, which are sufficient for a single site. However, basic 9-1-1 is not sufficient for identifying 9-1-1 in a campus environment or when using centralized SIP trunking to provide 9-1-1 for remote sites. Until now, there hasn't been a reliable way to do location-based 9-1-1 or E9-1-1.
For example, if you have a campus that has 15,000 users that are spread between five buildings and each building has four to five floors, how do you ensure that emergency services will arrive at the correct building and the correct floor? In my experience working for a large telecommunications hardware manufacturer, we created a database that tied the Media Access Control (MAC) address of a user's phone to a physical location. If the phone set was moved to a new location, someone had to update the location. This is not a big issue if users don't move their phones very often. However, with Communications Server, configuring 9-1-1 wasn't quite that simple because a user's portable computer also serves as their phone, and they may dial 9-1-1 using any network connection-wired, wireless LAN, or cellular. How do you determine the location of the user?
One solution I have seen customers use in earlier Unified Communications deployments included putting stickers on users' portable computers that said, "No 9-1-1." to remind users not to use Communicator to dial 9-1-1 and to find a physical phone or use a cell phone. Another solution I saw involved setting a default location for a user, and then provisioning a local trunk for each location. In an emergency, the local trunk notified the local Public Safety Answering Point (PSAP) or routed the 9-1-1 call to a campus security desk that dispatched emergency services. Each of these solutions has drawbacks and in some states violates the requirements for E9-1-1.
This problem has been solved in Lync Server 2010 by implementing National Emergency Number Association (NENA) 08-001 Interim VoIP Architecture for Enhanced 9-1-1 Services (i2).
There are two ways that 9-1-1 identifies the location from which a user calls. Either the user enters a location manually or the location is discovered automatically by matching the user's network location with the physical location that the administrator configured in the Location Information Server.
The Location Information Server gives the endpoint its physical location. This location is determined by the switch location, subnet, or the MAC address of the wireless base station. These network locations are matched to a physical street address, and then the street address is matched against the Master Street Address Guide. The Master Street Address Guide is the definitive list of addresses within a given PSAP.
After the Location Information Server is populated with the network and physical locations, the next step is to configure the SIP trunk for the emergency services gateway provider. This trunk will send the addresses to the Master Street Address Guide for validataion. The Location Information Server has to validate the physical location with the Master Street Address Guide of the PSAP. For example, if the administrator enters 123 West Elm Street, the Master Street Address Guide validated address might be 123 W Elm ST. This validation occurs over the SIP trunk that is identified as an emergency services provider trunk. The administrator gets a report back that indicates which addresses are valid and which are not. The administrator will have to modify the address until the address is valid.
When Lync 2010 registers with the Front End Server, Lync sends its network information to the Front End Server, and then checks if the network is enabled for E9-1-1. If the administrator has enabled the network for E9-1-1, the Front End Server returns a Location Information Server URI to Lync. Lync then connects to the Location Information Server and sends the network information.
The Location Information Server takes the network location, which can be identified by the wireless access point (WAP) Basic Service Set Identifier (BSSID), MAC address, IP version 4 (IPv4) subnet, or Link Layer Discovery Protocol (LLDP) switch or LLDP switch port, and then maps these to a physical mailing address. As a result, the wire map (which is a mapping of network elements to physical locations with the Location Information Server) is built. Figure 1 illustrates how this mapping works.
Figure 1. Mapping for Location Information Server
Note The WAP and subnet are the only mechanisms that allow all client types to work. A MAC address requires a third party to track a hardware MAC address to a location by using Simple Network Management Protocol (SNMP). Link Layer Discovery Protocol is supported only with Lync 2010 Phone Edition.
In a 9-1-1 enable network, Lync will be sent a Presence Information Data Format Location Object (PDIF-LO) that identifies the physical location of a user. This is sent anytime the user places a 9-1-1 call.
This section explains how a 9-1-1 call works in a network that is enabled for 9-1-1 (Figure 2).
Figure 2. 9-1-1 call process in a 9-1-1 enabled network
Note. The emergency services provider also has the option to add the security desk in as a conference.
This section explains how a 9-1-1 call works in a network that is not enabled for 9-1-1 (Figure 3).
Figure 3. 9-1-1 call process for a network that is not enabled for 9-1-1
Note. The emergency services provider has the option to add the security desk in as a conference.
The addition of E9-1-1 features that Microsoft has incorporated into the Lync Server 2010 infrastructure along with the E9-1-1 partners ecosystem has solved the issues of E9-1-1 in a mobile Unified Communications environment. Administrators can have confidence implementing Lync Server in a campus environment. Now, instead of stickers telling users not to use the phone for 9-1-1 or sending reminders to users when they log on, it is possible to direct emergency personnel to a user's location whether they are on a 15,000-user campus or sitting in a hotel.
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