session timer, 52 media announcements field, 168 signaling functions, 1-2 media capability/negotiation capabilities, text-based encoding, 188-89 Trapezoid, 49 message form, 164 URIs, 99-100 origin field, 165-66 user agents, 43-44 protocol version field, 165 warning codes, 156-57 session name and information field, 166 SIP for Telephones (SIP-T), 177 text coding, 164 S/MIME encryption, 59-60 time field, 167 stateful proxies, 214-18 URI field, 166 stateless proxies, 214-18 use of, 169-71 Stream Control Transport Protocol Session-Expires header field, 153 (SCTP), 7-8 Session Initiation Protocol. See SIP defined, 7 sessions as layer 2 transport protocol, 8 establishment example, 17-25 multihoming, 8, 41 negotiation, 126 transport, 41 RTP, 174 STUN protocol, 63-65 timer, 52 address translation types, 65 signaling protocols, 1-2 client, 63 Simple Mail Transport Protocol (SMTP), 3 defined, 63 Simple Traversal of UDP through NATs. illustrated, 64 See STUN protocol server, 63 Subject header field, 135 3GPP architecture and, 201-2 SUBSCRIBE method, 86-89 Index Accepted response to, 87 common schemes, 98 defined, 86 device, 26 Event header field, 88 globally routable contact, 263 example call flow, 87 port number, 99 mandatory header fields, 89 SIP, 99-100 refresh, 88 telephone scheme, 100 See also Methods user, 26 Subscription-State header field, 153 uniform resource locators (URLs), 1 success responses, 112 defined, 12 Supported header field, 136 format, 12 IM, 101 tags, 102 presence, 101 telephone URLs, 100-101 telephone, 100-101 Telephony Gateway Registration Protocol Universal Plug and Play (UPnP) Protocol, (TGREP), 47 Telephony Routing over IP (TRIP), 47 Unsupported header field, 155 Timestamp header field, 136-37 UPDATE method, 96-98 To header field, 137, 138 defined, 96 Transmission Control Protocol (TCP), example, 97 1, 5, 6-7 mandatory header fields, 98 congestion control, 40 See also Methods connections, 39 User-Agent header field, 137-38 defined, 6 user agents (UA), 43-44 disadvantages, 40 acknowledgment discard