A switched emergency call (e.g., a 911 call, an alarm company call) forwarded by a telematics call center is converted into a session initiation protocol (SIP) packetized phone call at the call center, and routed over an IP network, for presentation to an emergency services gateway, which connects to...http://www.google.com.tw/patents/US8150364?utm_source=gb-gplus-share專利 US8150364 - Enhanced E911 network access for a call center using session initiation protocol (SIP) messaging
