RFC 3665: Session Initiation Protocol (SIP) Basic Call Flow Examples

Publisher

RFC Editor / IETF

URL

https://www.rfc-editor.org/rfc/rfc3665.html

Published

2003-12-01

Updated

unknown

Accessed

2026-09-23

HTTP status

200

License

IETF Trust; RFC text may be reproduced subject to the RFC copyright notice; no-redistribution; short excerpts and locators only

Source notes citing this source

• In the RFC 3665 successful registration example the first REGISTER is answered with 401 Unauthorized carrying a challenge, the UA resends REGISTER with credentials computed from that challenge, and the server then returns 200 OK. in context
• In the RFC 3665 unsuccessful registration example, a REGISTER carrying credentials is answered with another 401 Unauthorized because the password does not match the one set for the account. in context
• In the RFC 3665 registration example the credentialed retry REGISTER keeps the same Call-ID as the challenged REGISTER and increments CSeq from 1 to 2. in context
• A REGISTER with no Contact header field is a query; in the RFC 3665 example the server answers with 200 OK listing the current registrations in Contact header fields. in context
• When a trace shows a second 401 or 407 in reply to a REGISTER that already carries Authorization or Proxy-Authorization, the likeliest reading is that the credentials (username, password or realm) were rejected, not that the first challenge went unanswered. inferred in context
• Cancelling all of a user's registrations uses a REGISTER with Contact: * and Expires: 0, and the server responds 200 OK after clearing the contact list. in context
• The RFC 3665 contact-list update example shows an authenticated REGISTER being accepted with 200 OK without a new 401 challenge. in context
• RFC 3665 includes reference flows for a session through a SIP ALG (Section 3.5) and a session with a re-INVITE caused by an IP address change (Section 3.7). in context
• RFC 3665, 'Session Initiation Protocol (SIP) Basic Call Flow Examples', was published in December 2003 as BCP 75. in context
• RFC 3665 labels the messages in each call flow diagram F1, F2 and so on, and gives the full text of each numbered message after the diagram. in context
• RFC 3665 Sections 3.8 to 3.11 give reference flows for unsuccessful sessions: no answer, busy, no response from the user agent, and temporarily unavailable. in context
• Section 2 of RFC 3665 gives registration call flows, including a new registration, contact list update and query, cancellation, and an unsuccessful registration (Section 2.5). in context

Cite this source record

APA

WarmTransfer. (2003, December 1). RFC 3665: Session Initiation Protocol (SIP) Basic Call Flow Examples. WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-3665-basic-call-flows

BibTeX

@misc{warmtransfer-rfc-3665-basic-call-flows,
  title  = {RFC 3665: Session Initiation Protocol (SIP) Basic Call Flow Examples},
  author = {{WarmTransfer}},
  year   = {2003},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-3665-basic-call-flows},
  note   = {RFC Editor / IETF, accessed 2026-09-23}
}