Core specification of the current revision of SIP.
RFC category: Standards Track.
SIP category: Core specifications.
Obsoletes: RFC 2543.
Authors:, , , , , , , .
Number of pages: 269.
Working Group: SIP.
Definitions (see Glossary)
User Agent Core
Session Establishment and Tear-down
Call Is Being Forwarded
Method Not Allowed
Proxy Authorization Required
Request Entitiy Too Large
Request-URI Too Long
Unsupported Media Type
Unsupported URI Scheme
Interval Too Brief
Call/Transaction Does Not Exist
Too Many Hops
Not Acceptable Here
Server Internal Error
Version Not Supported
Message Too Large
Does Not Exist Anywhere
RFC 3261 references
("DoD Standard Transmission Control Protocol", normative reference ),
("User Datagram Protocol", normative reference ),
("Requirements for Internet Hosts - Application and Support", normative reference ),
("The MD5 Message-Digest Algorithm", informational reference ),
("Randomness Recommendations for Security", normative reference ),
("Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", normative reference ),
("RTP: A Transport Protocol for Real-Time Applications", informational reference ),
("Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", normative reference ),
("An Extension to HTTP: Digest Access Authentication", informational reference ),
("Common Internet Message Headers", informational reference ),
("Key words for use in RFCs to Indicate Requirement Levels", normative reference ),
("Communicating Presentation Information in Internet Messages: The Content-Disposition Header Field", normative reference ),
("Augmented BNF for Syntax Specifications: ABNF", normative reference ),
("The TLS Protocol Version 1.0", normative reference ),
("IETF Policy on Character Sets and Languages", normative reference ),
("UTF-8, a transformation format of ISO 10646", normative reference ),
("Real Time Streaming Protocol (RTSP)", informational reference ),
("SDP: Session Description Protocol", normative reference ),
("The mailto URL scheme", informational reference "),
("Uniform Resource Identifiers (URI): Generic Syntax", normative reference ),
("Security Architecture for the Internet Protocol", normative reference ),
("vCard MIME Directory Profile", informational reference ),
("SIP: Session Initiation Protocol", informational reference ),
("Hypertext Transfer Protocol – HTTP/1.1", normative reference  and [HX.Y] with reference to sections),
("HTTP authentication: Basic and Digest Access Authentication", normative reference ),
("Cryptographic Message Syntax", normative reference ),
("S/MIME Version 3 Message Specification", normative reference ]),
("URLs for Telephone Calls", normative reference ),
("Internet Message Format", normative reference ),
("The LDAP Data Interchange Format (LDIF) - Technical Specification", informational reference ),
("Congestion Control Principles", informational reference ),
("Stream Control Transmission Protocol", normative reference ),
("The SIP INFO Method", informational reference ),
("Megaco Protocol Version 1.0", informational reference ),
("MIME media types for ISUP and QSIG Objects", normative reference ),
("SIP: Locating SIP Servers", normative reference ),
("An Offer/Answer Model with SDP", normative reference ),
("Advanced Encryption Standard (AES) Ciphersuites for Transport Layer Security (TLS)", normative reference ),
("Session Initiation Protocol (SIP) Basic Call Flow Examples", informational reference ),
("Session Initiation Protocol (SIP) Public Switched Telephone Network (PSTN) Call Flows", informational reference ),
R. Pandya, "Emerging mobile and personal communication systems," IEEE Communications Magazine, Vol. 33, pp. 44–52, June 1995 (informational reference ),
E. M. Schooler, "A multicast user directory service for synchronous rendezvous," Master's Thesis CS-TR-96-18, Department of Computer Science, California Institute of Technology, Pasadena, California, Aug. 1996 (informational reference ),
E. M. Schooler, "Case study: multimedia conference control in a packet-switched teleconferencing system," Journal of Internetworking: Research and Experience, Vol. 4, pp. 99–120, June 1993. ISI reprint series ISI/RS-93-359 (informational reference ),
H. Schulzrinne, "Personal mobility for multimedia services in the Internet," in European Workshop on Interactive Distributed Multimedia Systems and Services (IDMS), (Berlin, Germany), Mar. 1996 (informational reference )
RFC 3261 is referenced by
RFC 3325 ("Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks", normative reference ).
The following sections of RFC 3261 have been updated:
XXX will be done as those RFCs are processed.
See also the IETF tools' status page for draft-ietf-sip-rfc2543bis
Number of pages: 179.
see draft-ietf-sip-rfc2543bis-00, appendix F
Number of pages: 177 (-2).
see draft-ietf-sip-rfc2543bis-01, appendix H
Number of pages: 171 (-6).
see draft-ietf-sip-rfc2543bis-02, appendix H
Number of pages: 190 (+19).
see draft-ietf-sip-rfc2543bis-03, appendix I
Number of pages: 195 (+5)
see draft-ietf-sip-rfc2543bis-04, appendix J
Number of pages: 221 (+26).
see draft-ietf-sip-rfc2543bis, section 33
Number of pages: 278 (+57).
see draft-ietf-sip-rfc2543bis-06, section 35
[H]ere are the changes:
1. single consolidated "changes from rfc2543" section, listing major stuff.
2. BNF converted to rfc2234, countless bugs fixed based on comments
3. new loose route text incorporated. Please read this. The text is different from what Robert had described on the list. Whilst incorporating that text, we ran into a case that didn't work. TUrns out the fix simplified the whole thing even further. Based on robert's note, a proxy that wanted to route to a strict router would need to dig up the first loose router in a route set, say A, and replace that route entry with A, target, A, where target is the current r-uri. That is not the case now; it simply appends the r-uri to the bottom-most route element. This improves the backwards compatibility story, improves proxy performance, and makes things much more self consistent. Proxy processing of route/record-route is now shrunk considerably from bis-05 and bis-06.
4. split references into normative and non-normative.
5. incorporated text on generalized offer/answer mappings to SIP requests and responses
6. Reduced usage of 70 as max-forwards value from MUST to SHOULD
7. Included fix for open issue #58. When UAS generates an offer in a 2xx to re-invite, it uses the broadest SDP possible that it belives will not be rejected by its peer.
8. Added some S/MIME error cases.
9. Fixed normative strengths of S/MIME support (MUST for signed-data and certs-only).
10. Strengthened TLS/IPSec wording (fixing nits).
11. S/MIME should now be able to reuse root CAs used to verify TLS/IPSec keys.
12. Added brief statement to start of threat model section describing threat environment.
13. Added eavesdropping to threats based on body modification.
14. clarified conditions under which multiple headers can be folded into one header with comma separated values. Also pointed out exception for the Auth headers.
15. Max-Forwards needs to be between 1 and 255.
16. Added anonymous username and password for digest.
17. Clarified usage of timestamp delay parameter.
Number of pages: 268 (+7).
Mentions SIPS-URIs in introduction.
Removal of mentioning of 100rel stuff in various places.
Added definiton of Address-of-Record, Core, Header Field, Header Field Value, Target Refresh Request.
Clean-up on terminoligy (eg., consequent use of header field).
Added a sentence outlining the exception from that Request-URI and To-URI SHOULD initially be the same.
Clarifications on the use of the SIPS URI scheme.
XXX continue the diff at section 126.96.36.199 Via
Number of pages: 276 (+8).
XXX To be done.
Number of pages: 269 (-7).
Definition for Header Field and Header Field Value extended.
Define default charset for text media types to be UTF-8.
Specify that a stateless UAS has do always give the same response to the same request.
A missing expiration time does not imply a SHOULD of an hour any more but means the client wants the server to choose.
Mentions that there may be more than one offer/answer exchange going on for a single INVITE if there are more than one branch.
Adding a note pointing out that the Via branch will be different for every time a spiralling request passes by the same proxy.
Rephrase the conditions for matching a request to a transaction using a numbered list.
Enforce changing of Via if changing the transport protocol due to MTU.
Force isdn-subaddress and post-dial parameters to be first when turning tel-URIs into SIP- or SIPS-URIs.
Increase upper limit of Expires value from (231)-1 to (232)-1.
Give rules for comparing From header fields in section 20.20.
70 is only the recommended initial value.
Add qop parameter to Proxy-Authenticate and WWW-Authenticate examples.
Allow Retry-After with a 500 (Server Internal Error).
Remove reference to RFC 2116 for the Server header field.
Mention compact form for Supported header field.
Mention rules for a two Via being identical to section 20.42.
Use of Usupported header field in 420 (Bad Extension) upgraded to MUST.
Added To tag to 200 (OK) for registrar call flow.
"@" made part of userinfo.
user needs to be at least one character long.
Accept* and Allow may be empty.
ainfo, digest-cln: no more square brackets.
Timestamp: LWS before delay.
Excerpts from RFCs and Internet Drafts:
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