RFC 3262: Reliability of Provisional Responses in the Session Initiation Protocol (SIP)

Publisher

IETF / RFC Editor

URL

https://www.rfc-editor.org/rfc/rfc3262.html

Published

2002-06-01

Updated

unknown

Accessed

2026-09-24

HTTP status

200

License

IETF Trust legal provisions; RFC text may be reproduced with attribution; short excerpts and locators only

Source notes citing this source

• RFC 3262 forbids sending 100 (Trying) reliably; only provisional responses numbered 101 to 199 may be sent reliably. in context
• Under RFC 3262, if the initial INVITE carries the 100rel option tag in a Require header, the UAS must send every non-100 provisional response reliably. In a Supported header the tag only signals capability. in context
• RFC 3262 defines the PRACK method to acknowledge a reliable provisional response, with the RSeq header in the provisional response and the RAck header in the PRACK. in context
• Under RFC 3262 a reliable provisional response is retransmitted with exponential backoff starting at T1 until a PRACK arrives, or for up to 64*T1 seconds. in context
• RFC 3262, which defines reliable provisional responses in SIP, is a Standards Track (Proposed Standard) RFC published in June 2002 and gives PSTN interworking as its motivation. in context
• RFC 3262 allows session descriptions to be exchanged in reliable provisional responses and in PRACK, so the session can be established before the call completes. in context
• When a UAC that sent an INVITE without an offer receives the offer in a reliable provisional response, it answers in the PRACK. in context
• When the INVITE contained no offer and a reliable provisional response is the first reliable message sent back to the UAC, the offer must appear in that reliable provisional response. in context

Cite this source record

APA

WarmTransfer. (2002, June 1). RFC 3262: Reliability of Provisional Responses in the Session Initiation Protocol (SIP). WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-3262-reliable-provisional

BibTeX

@misc{warmtransfer-rfc-3262-reliable-provisional,
  title  = {RFC 3262: Reliability of Provisional Responses in the Session Initiation Protocol (SIP)},
  author = {{WarmTransfer}},
  year   = {2002},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-3262-reliable-provisional},
  note   = {IETF / RFC Editor, accessed 2026-09-24}
}