Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Figure 16.2 Emergency VoIP calling using the PSTN emergency infrastructure

Emergency Communication Services

Emergency calls, as described in the previous sections, are made to assist indi-
vidual users under normal circumstances (that is, when no general emergen-
cies occur, such as natural or man-made disasters).
During an emergency, the network resources may not be able to handle the
surge of communications, and preference must be given to rescue, govern-
ment, and military callers. Limited network resources could be the ports on
PSTN gateways, and bandwidth limitations on access links or on bandwidth
constrained global satellite links, for example. The Emergency Telecommuni-
cations Service (ETS) has been implemented in the PSTN and an excellent
overview of implementing ETS in IP telephony is provided in RFC 4190 [8].
The work on emergency services using IP and the Internet has focused on a
few critical topics, most notably:

■■ Requirements for resource priority mechanisms for SIP [9]

■■ The solutions for communications resource priority for SIP [10]

■■ SIP reason header for preemption events [11]

■■ Preemption of network resources used by SIP in government and mili-

tary networks, and in single administrative domains in general

Emergency

SIP Proxy

PSTN

GWY

Master Street

Address Guide

Automatic

Line

Identification

PSAP

SIP UA or

Endpoint

LI

Server

VoIP

Positioning

Emergency Services

Provider Network

VoIP Domain

SIP

SIP

LO LO

Routing

Info

Routing

Numbers

Civic

Address

Validation of

Civic Location

Call-back and

provider info

SS7

Emergency

Routing DB

Validation

Databases

Emergency

Switch (911)

Emergency and Preemption Communication Services 281