emergency numbers, various mechanisms exist. GSM mobile phones use the
SIM card inside the device, while 3G mobile phones rely on the 3GPP-specific
network-based solutions. We expect emergency calling on the Internet to use
URIs that have global significance and are also simple to remember in an
emergency.Identifying an Internet Emergency Call: The SOS URI
The emergency URI defined for the Internet is sos[5], and it uses the feature
tag for the caller Feature Set Preferences based on RFC 3841. The proposed val-
ues for “sos” for anumber of emergency services as shown here below. The
various services are invoked using a new media feature tag called
“sip.emergency-service”.The feature tag indicates the type of service
requested as shown in Table 16.3.
The outbound SIP proxy will check whether an emergency phone number has
been dialed and will translate it into a sosURI for call routing. The sosURI can
also be used directly in the SIPRequest-URIby the mobile Internet device.Internet Emergency Call Routing
Emergency call routing over the internet is illustrated in Figure 16.1, where the
following can be highlighted:
■■ The location information may be made available to the device itself
using one of the methods discussed in the preceding sections, for exam-
ple being provided by the network infrastructure and loaded by DHCP
at same time with acquiring an IP address.
■■ The user could also consult a directory to find the the right PSAP URI.
■■ The emergency call could also be routed by the VoIP service provider, if
one is used, to the SIP proxy for emergency call routing support (ECRS).Table 16.3 Internet Emergency Services for SIP
SERVICE TAG
General emergency service sos
Fire brigade sos.fire
Marine guard sos.marine
Mountain rescue sos.mountain
Police (law enforcement) sos.police
Ambulance, emergency medical service sos.rescue
Testing, not a real emergency call sos.test278 Chapter 16