E9-1-1 Solutions for IP or VoIP MLTS
The first thing to understand is that IP-connected devices differ from Legacy or TDM connected devices in the way that they are recognized by the MLTS. Unlike TDM systems that identify endpoints exclusively with telephone numbers, packet-based systems use IP addresses.28 Furthermore, IP based MLTS permit users to unplug, move their phone, plug in and get dial tone at a new location, which complicates the caller location reporting for emergency calls.
The decision of where telephone numbers are assigned is critical. This is because data networking switches may be deployed to serve an entire small office. They may be deployed to provide connectivity to a floor in a building, several floors, or an area of one floor of a building. Deployment of hardware depends on a number of business and technology decisions. These deployment decisions must include careful consideration of the need to provide accurate and actionable emergency location determination. Thus, the E9-1-1 solution would involve mapping the telephone number with the port, group of ports or switch in the firm's location database.
Fixed vs. Nomadic IP users.29 Another important issue in determining the emergency location of an MLTS caller is whether the user can move his telephone device between different locations on the network.
Fixed/Static refers to an IP end-point that cannot move, is always in the same location and always accesses a network from the same point.
Nomadic: A user is said to be nomadic if it/she/he is constrained within an access network such that the user's location can be represented as a definitive civic address for that network attachment. A user can move from one network attachment to another but cannot maintain a session during that move. If the user is able to move outside the definitive civic address without losing network attachment then the user is considered to be mobile, not nomadic.
Dynamic IP Addresses. Dynamic Host Configuration Protocol (DHCP) is a software process that allows portability of endpoint devices within data networks, such as Local Area Networks, Wide Area Networks or Enterprise Networks.30 Prior to DHCP, each device on a data network had a statically assigned IP address. A DHCP server houses a table that maps between the endpoints and the available IP address. With DHCP, the IP address becomes dynamically assigned. Rather than a hard coded IP address, the software of the device is set up to receive an IP address during a registration process that takes place when a device is activated on the network.
28 In IP Caller Location Reporting - Layer 2 Switch Port Level there are a number of deployment options. Because data networking switches communicate with the endpoint devices using IP addresses, choices of where to relate telephone numbers to the endpoint need to be made. The closer that telephone number is assigned to the location of the end-user, the more promptly a public safety first responder can find the person during an emergency. Telephone numbers might be assigned to the individual connection points between the device and the data networking switch. These are called ports. Each port may have an individual telephone number assigned to it. Telephone numbers might also be assigned to a group of ports or a single number could be assigned to the entire switch. NENA 06-502 at 29.
29 NENA 08-752 at 12.
30 NENA 06-502 at 30.
