197 UASs (User Agent Servers), 116 user registration, 195 UDP (User Datagram Protocol), 58 visited domain registration, 196 UNI (User-to-Network Interface), 18 third-party call control, unicast routing, 62 SIP extensions, 181-182 upper-layer end-to-end protocols, 41 three-way handshake, 121 URLs (Uniform Resource Locators), 97 timestamps, RTP packets, 71 addressing SIP resources, 111 toolkit, IETF, 42 SDP session descriptions, 84 topologies, 3-4 user plane, 8, ISUP, 27 traffic, real-time transport, 70-71 users transactions, SIP, 116, 150 mobility, 96 CANCEL, 148 registration INVITE, 145-146 3G mobile systems, 195 mid-session, 169 location, 97 multiple message bodies, 170 non-successful final responses, 146 successful final responses, 148 Index Web sites, SIP-related, 221 Dean Willis, 225 versions of SIP, 91-92 Henning Schulzrinne, 223 Via headers, SIP requests, 142 IETF, 221-223 virtual circuits, 32 RFCs, 221 differences from datagrams, 34 SIP Forum, 226 establishment delay, 35 Willis, Dean, Web site, SIP information, 225 routing, 33 working groups, IETF, 48-49 visited domain registration, X.25, PSTN, 36 3G mobile systems, 196 weaknesses circuit-switched networks, 7 digital transmission, 14 packet switching, 36 ABOUT THE AUTHOR Gonzalo Camarillo is the Principal Systems Expert with the Advanced Sig- naling Research Lab of Ericsson in Helsinki, Finland. An active participant in the IETF's SIP Working Group since its inception, he co-authored several contributions on SIP-related matters. He is also a frequent speaker at VoIP conferences and the Ericsson representataive in the SIP Forum. He received an M.Sc. degree in Electrical Engineering from Universidad Politecnica de Madrid and another M.Sc. degree-also in Electrical Engi- neering-from the Royal Institute of Technology in Stockholm. He is con- tinuing his studies as a Ph.D. candidate at Helsinki University of Technology. Copyright 2002 The McGraw-Hill Companies, Inc. Click Here for Terms of Use. SIP HANDBOOK SERVICES, TECHNOLOGIES, AND SECURITY OF SESSION INITI