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The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds, Third Edition by Gonzalo Camarillo, Miguel A. García-Martín

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Chapter 13

Emergency Calls on the Internet

13.1 Introduction

This chapter is devoted to the complex topic of IP-based emergency calls. What makes IP-based emergency calls a complex issue? First of all, an emergency call needs to be routed to the closest Public Safety Answering Point (PSAP). This requires the call to be routed to the PSAP based on the caller’s location, which in turns requires the caller’s location to be determined roughly. Furthermore, it also requires a mechanism to translate the location into the real URI of the PSAP. All of these issues make IP-based emergency calls complex in comparison with regular IP-based calls using SIP.

There are three different types of emergency communications, of which this chapter covers just the first.

Citizen-to-authority communications. This type of communication refers to users dialling an emergency number, such as 112 in Europe or 911 in the USA. Usually these are referred to as emergency calls.

Authority-to-citizen communications. This typically refers to national emergency centers broadcasting alerting information related to emergency situations. For example, in the case of a rough weather condition, such as a hurricane or a tsunami, an alert can be issued to the population providing instructions for their safety. In some cases, this type of emergency communication may require warning messages or instructions to be launched to all citizens or a groupof them who are located in a determined geographical area, e.g., where a disaster ...

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