 160-162 protocols, 2 peer-to-peer relationship, 163 user plane, 8 PRACK requests, 168 SIMPLE (SIP for Instant Messaging and provisional responses, 166 Presence Leveraging Extensions), 200 reliable delivery of provisional simplicity, IETF protocol design, 44 responses, 166 sending commands, 186 Index session transfers, 184 REGISTER requests, 125 session type independence, 164 registering user locations, 97 third-party call control, 181-182 registrars, 105 forking proxy servers, 104 requests, 117 functionality, 94 Call-ID headers, 135 group addresses, 102 Contact headers, 136 historical overview, 90 Csec, 137-138 HTTP basis, 110 From headers, 138 IETF toolkit, 106 headers, 134 Internet component reuse, 110 Record-Route headers, 139-140 interoperability, 109 request line, 132 interoperability events, 94 Route headers, 139-140 INVITE requests, 119-120, 145 Via headers, 142 INVITE responses, 146 responses location servers, 105 format, 132 messages reason phrases, 117 bodies, 142, 144 status codes, 117-118 text-based, 130 status line, 133 multicast conferences, 215 RFC example, 227 non-successful final responses, 146 S/MIME confidentialty, 189 OPTIONS requests, 126 scalability, 110 programming apps, 113 security, 187 proposed standards, 93 servers, 116 proxy calls, 151-157 session proxy servers, 103, 126 descriptions, 95, 108 distribution, 129 distribution, 95 group addresses, 104 establishment, 94, 108 PSTN internetworking, 204 SMTP routing basis, 112 extensions, 210 stateful proxy servers, 127-128 gateways, 206 stateless proxy servers, 129 high-capacity gateways, 209 successful final responses, 148 low-capacity gateways, 207-208 three way handshake, 121 message bodies, 211 transactions, 116, 150 PINT, 213 transport layer protocols, 144 Index UACs (User Agent Clients), 116 streaming services, Internet, 59 UAs (User Agents), 100-102 strengths UASs (User Agent Servers), 116 circuit-switched networks, 6 URLs (Uniform Resource digital transmission, 14 Locators), 97,111 packet switching, 35 user mobility, 96 Strowger, Alm