Providing Emergency Call Services for SIP-based Internet Telephony

If Internet Telephony is to offer a full replacement for traditional telephone services, it needs to provide emergency call services. In the United States, emergency calls are known as 911 services, based on the number dialed. This note desccribes some options for providing enhanced emergency service, i.e., emergency calls that allow emergency response centers to determine the address where the caller is located. This is made more difficult by the temporary nature of IP addresses, the large number of ISPs and their lack of legal responsibility for emergency services and the ability of many Internet terminals to be connected to the Internet at different locations. This note explores some of the requirements and design choices.