9 PSTN, 47 Join, 143-44 PSTN to SIP through, 222-25 Max-Forwards, 147 SIP to PSTN through, 218-22 message body, 158-60 global error responses, 125-26 MIME-Version, 160 globally routable contact URIs, 263 Min-Expires, 154 Min-SE, 154-55 H.323 Organization, 134 call flow illustration, 184 P-Asserted-Identity, 147 call tear-down sequence, 186 P-OSP-Auth-Token, 145-46 comparison, 187-91 P-Preferred-Identity, 147 defined, 181 Priority, 144-45 end points, 183 Privacy, 145 example, 184-87 Proxy-Authenticate, 155 FastStart connections with, 188 Proxy-Authorization, 145, 146 introduction to, 181-83 Proxy-Require, 145 network elements, 182 RAck, 152-53 niche areas, 190 Reason, 147-48 protocols referenced by, 183 Record-Route, 134-35 to SIP call flow, 230-35 Referred-By, 148-49 versions, 187 Refer-To, 148 header fields, 127-60 Reject-Contact, 150-51 3GPP, 203-4 Replaces, 150 Accept, 140 Index Reply-To, 149-50 Internet Assigned Number Association request, 140-53 (IANA), 5 request and response, 128-40 Internet Engineering Task Force (IETF), 2-3 Request-Disposition, 151 Internet Emergency Preparedness Require, 151-52 (IEPREP), 263 response, 153-57 PINT working group, 3 Response-Key, 152 Request for Comments (RFCs), Retry-After, 135, 136 2, 267-69 Route, 152 SIMPLE working group, 3 RSeq, 156-57 SIPPING working group, 3 rules, 127 SIP-related work status, 262 Server, 155 SPIRITS working group, 3 Session-Expires, 153 working groups, 2-3 Subject, 135 Internet layer, 4-5 Subscription-State, 153 Internet Multicast Backbone Network Supported, 136 (MBONE), 13 Timestamp, 136-37 Internet Multimedia Protocol stack, 4-9 To, 137, 138 application layer, 8-9 Unsupported, 155 illustrated, 4 User-Agent, 137-38 Internet layer, 4-5 Via, 138-40 physical layer, 4 Warning, 156 transport layer, 5-8 WWW-Authenticate, 156 Internet Protocol. See IP hearing impairment design team, 262 Internet service providers (ISPs), 25 HTTP Digest authentication, 58 INVITE method, 72-74 HyperText Transport Protocol (HTTP), defined, 72 3, 107 example, 73-74 for existi