Reply-To header field, 149-50 Reply-To, 149-50 request and response header fields, 128-40 Request-Disposition, 151 Alert-Info, 128-29 Require, 151-52 Allow-Events, 129 Response-Key, 152 Call-ID, 129-30 Route, 152 Contact, 130-32 Session-Expires, 153 CSeq, 132, 133 Subscription-State, 153 Date, 132-33 See also Header fields Encryption, 133 requests. See Methods From, 133-34 Require header field, 151-52 Organization, 134 response code, 107 Record-Route, 134-35 HTTP, 107 Retry-After, 135, 136 number, 21 Subject, 135 use of, 107 Supported, 136 response header fields, 153-57 Timestamp, 136-37 Authentication-Info, - 153-54 To, 137, 138 defined, 153 User-Agent, 137-38 Error-Info, 154 Via, 138-40 Min-Expires, 154 Request-Disposition header field, Min-SE, 154-55 Proxy-Authenticate, 155 Request for Comments (RFCs), 2, 267-69 RSeq, 156-57 RFC 2543, 267-68 Server, 155 RFC 3261, 268-69 Unsupported, 155 Index Warning, 156 481 Dialog/Transaction Does WWW-Authenticate, 156 Not Exist, 119 See also Header fields 482 Loop Detected, 119 Response-Key - header field, 152 483 Too Many Hops, 119-20 response(s), 107-26 484 Address Incomplete, 120 100 Trying, 109 485 Ambiguous, 120-21 180 Ringing, 109 486 Busy Here, 121 181 Call Is Being 487 Request Terminated, 122 Forwarded, 109 488 Not Acceptable Here, 122 182 Call Queued, 109 489 Bad Event, 122 183 Session Progress, 110 491 Request Pending, 122 200 OK, 112 493 Request Undecipherable, 202 Accepted, 112 122-23 300 Multiple Choices, 113 501 Not Implemented, 124 301 Moved Permanently, 113 502 Bad Gateway, 124 302 Moved Temporarily, 113 503 Service Unavailable, 124 305 Use Proxy, 113 504 Gateway Timeout, 124 380 Alternative Service, 113 505 Version Not Supported, 400 Bad Request, 114 401 Unauthorized, 114 513 Message Too Large, 125 402 Payment Required, 114 600 Busy Everywhere, 125 403 Forbidden, 115 603 Decline, 125 404 Not Found, 115 604 Does Not Exist 405 Method Not Allowed, 115 Anywhere, 125 406 Not Acceptable, 115 606 Not Acceptable, 125 407 Proxy Authentication classes, 108 Required, 