6-77 response, 125 mandatory headers, 77 See also Methods 606 Not Acceptable response, 125 call flow Accept-Contact header field, 140-41 Accept-Encoding header field, 141 3GPP, 235-54 Accept header field, 140 with authentication, proxies, and Accept-Language header field, 141-42 record-route, 207-14 ACK method, 77-79 authentication digest, 59 application/sdp message body, 77 examples, 207-59 defined, 77 H.323, 184 end-to-end, 77, 78 H.323 to SIP, 230-35 example, 78 NOTIFY method, 87 hop-by-hop, 77, 78 parallel search, 225-30 mandatory headers, 79 PSTN to SIP, 222-25 See also Methods REFER method, 83 acknowledgment messages, 55-56 SIP to PSTN, 218-22 defined, 56 with stateless/stateful proxies, 214-18 UA generation, 55 SUBSCRIBE method, 87 Address Complete Message (ACM), 219 Call - ID header field, 129-30 Call - Info header field, 142 Index calls 429 Provide Referror cancellation race condition, 80 Identity, 118-19 H.323 to SIP, 230-35 480 Temporarily Unavail with proxy server, 25-30 able, 119 PSTN to SIP through gateway, 222-25 481 Dialog/Transaction Does queuing example, 110 Not Exist, 119 setup example, 254-56 482 Loop Detected, 119 SIP to PSTN through gateway, 218-22 483 Too Many Hops, 119-20 SIP with authentication, proxies, 484 Address Incomplete, 120 record-route, 207-14 485 Ambiguous, 120-21 SIP with stateless/stateful proxies with 486 Busy Here, 121 busy called party, 214-18 487 Request Terminated, 122 state information, 30 488 Not Acceptable Here, 122 CANCEL method, 79-81 489 Bad Event, 122 branch ID, 80 491 Request Pending, 122 defined, 79 493 Request Undecipherable, example, 81 122-23 mandatory headers, 81 defined, 113-14 proxies receiving, 80 See also Response(s) See also Methods Common Presence and Instant Message circuit associated signaling, 176 Presence Information Data Format client error responses, 113-23 (CPIM PIDF), 36 400 Bad Request, 114 conferencing design team, 262-63 401 Unauthorized, 114 congestion control 402 Payment Required, 114 TCP, 40 403 Forbidden, 115 UDP and, 39 404 Not Found, 11