ng dialog references, 73 INFO method, 93-94 Expires header, 73 defined, 93 mandatory headers, 74 example, 93-94 with no SDP message body, 72 mandatory headers, 94 See also Methods See also Methods IP, 1 informational responses, 108-11 addresses, 25-26 100 Trying, 109 mobility, 193-94 180 Ringing, 109 Multimedia Core Network Subsystem 181 Call Is Being (IMS), 201 Forwarded, 109 ISDN signaling, 176-77 182 Call Queued, 109 183 Session Progress, 110 ACM, 219 defined, 108 signaling, 176 See also Response(s) In-Reply-To header field, 143 Join header field, 143-44 instant messaging call flow example, 256-59 Max-Forwards header field, 147 example, 33-38, 92 media access control (MAC) addresses, 10 session, establishing, 92 media gateway controllers (MGCs), 47 transport, 90 media gateways (MGs), 47 URLs, 101 message bodies, 102-4 work, 264 format, 102-3 SIP: Understanding the Session Initiation Protocol message bodies (continued) Min-SE header field, 154-55 information types, 102 Mobile IP, 193-94 intended use, 102 3GPP reliance on, 202 MIME encoding, 103 defined, 193 number of octets in, 103 triangular routing, 194 SIP carrying of, 103 mobility message body header fields, 158-60 IP, 193-94 Allow, 158 midcall, 197-99 Content-Disposition, 158 personal, 194-95 Content-Encoding, 158 precall, 196 Content-Language, 158 scenarios, 198 Content-Length, 159 SIP, 194-201 Content-Type, 159-60 multicast, 12-13 Expires, 160 support, 60 MIME-Version, 160 uses, 60 See also Header fields multihoming, 8, 42 MESSAGE method, 90-93 Multipart Internet Mail Extensions (MIME) 200 OK response, 91 encoding, 103 defined, 90-91 example, 103-4 example, 92-93 mandatory header fields, 93 network address translators (NATs), 61-62 See also Methods address binding, 62 message transport, 38-42 problems, 61, 62 SCTP, 41-42 TCP and, 66-67 TCP, 40 transparency, 61 TLS, 40-41 traversal protocols/extensions, 62-68 NOTIFY method, 89-90 UDP, 38-39 methods, 71-104 defined, 89 ACK, 77-79 example, 90 BYE, 76-77 example call flow, 87 CANCEL, 79-81 mandatory header f