SIP: Session Initiation Protocol (RFC 3261)

Publisher

IETF

URL

https://www.rfc-editor.org/rfc/rfc3261

Published

2002-06

Updated

unknown

Accessed

2026-09-04

HTTP status

unchecked

License

IETF RFC; excerpts permitted with attribution

Claims citing this source

• A 400 Bad Request response means the server could not parse the request because of malformed syntax; the reason phrase should identify the specific syntax problem, such as a missing header field. fact in context
• A 401 Unauthorized response means the request requires user authentication; it is issued by user agent servers and registrars, distinct from 407 which is used by proxy servers. fact in context
• A 408 Request Timeout response means the server could not produce a response within a suitable time, for example because it could not locate the user, and the client may retry the unmodified request later. fact in context
• A 481 Call/Transaction Does Not Exist response means the UAS received a request that does not match any dialog or transaction it currently knows about. fact in context
• A 483 Too Many Hops response means the server received a request whose Max-Forwards header field had already reached zero, so the request was not forwarded any further. fact in context
• A 487 Request Terminated response means the original request was terminated by a BYE or CANCEL, and it is never sent as the response to a CANCEL request itself. fact in context
• A SIP dialog is a peer-to-peer relationship between two user agents that persists over time, identified by a Call-ID value plus a local and remote tag, and it is used to sequence and route messages between the two agents. fact in context
• For every 2xx response the UAC receives to an INVITE, the UAC core generates a separate ACK sent directly by the transport layer rather than the transaction layer, reusing the INVITE's CSeq number but with the method changed to ACK. fact in context

Cite this source record

APA

WarmTransfer. (n.d.). SIP: Session Initiation Protocol (RFC 3261). WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-3261

BibTeX

@misc{warmtransfer-rfc-3261,
  title  = {SIP: Session Initiation Protocol (RFC 3261)},
  author = {{WarmTransfer}},
  year   = {2002},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-3261},
  note   = {IETF, accessed 2026-09-04}
}