Patent ID: 8040905

Claim:
A method for establishing an emergency call, comprising: receiving, by a Proxy-Call Session Control Function entity, P-CSCF, an emergency call request message; if the emergency call request message contains an Internet Protocol Multimedia Subsystem Public User Identity, IMPU, in a Telephone Uniform Resource Identifier, TEL URI, format, generating, by the P-CSCF, an IMPU in a Session Initiation Protocol, SIP, URI format according to the IMPU in the TEL URI format; sending, by the P-CSCF, the IMPU in the TEL URI format and the IMPU in the SIP URI format to a Public Safety Answering Point, PSAP; and receiving, by the P-CSCF, an emergency callback from the PSAP according to the IMPU in the TEL URI format or the IMPU in the SIP URI format.