RFC 6026: Correct Transaction Handling for 2xx Responses to Session Initiation Protocol (SIP) INVITE Requests

Publisher

IETF / RFC Editor

URL

https://www.rfc-editor.org/rfc/rfc6026.html

Published

2010-09-01

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

IETF Trust Legal Provisions (BCP 78); no-redistribution; short excerpts and locators only

Source notes citing this source

• After RFC 6026, retransmissions of a 2xx response to INVITE are handled by the transaction user (the UAS core), not by the INVITE server transaction. in context
• A UAS core passes its 2xx response to the transport repeatedly, at an interval that starts at T1 seconds and doubles on each retransmission until it reaches T2 seconds. in context
• With the common T1 of 500 ms, 64*T1 is 32 seconds. A call that is answered and then torn down by the called side about 32 seconds later therefore matches the missing-ACK timeout, not a session-timer expiry. inferred in context
• RFC 6026 adds an Accepted state to both INVITE client and server transactions and says an element sending or receiving a 2xx to INVITE must not destroy the matching INVITE transaction state. in context
• The INVITE client transaction must not generate the ACK for a 2xx response; the UAC core sends that ACK in a new transaction. in context
• Under RFC 6026, a proxy must not forward a response for which it has no matching transaction state machine, so it can no longer statelessly forward stray 2xx responses. in context
• RFC 6026, published in September 2010, updates RFC 3261. in context
• RFC 6026 defines Timer L as 64*T1 for all transports: the time an INVITE server transaction stays in the Accepted state, which covers how long a UAS core may retransmit the 2xx while waiting for an ACK. in context
• RFC 6026 defines Timer M as 64*T1: the time an INVITE client transaction stays in the Accepted state, waiting for 2xx retransmissions or for further 2xx responses from other branches of a forked INVITE. in context

Cite this source record

APA

WarmTransfer. (2010, September 1). RFC 6026: Correct Transaction Handling for 2xx Responses to Session Initiation Protocol (SIP) INVITE Requests. WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-6026-invite-2xx-transactions

BibTeX

@misc{warmtransfer-rfc-6026-invite-2xx-transactions,
  title  = {RFC 6026: Correct Transaction Handling for 2xx Responses to Session Initiation Protocol (SIP) INVITE Requests},
  author = {{WarmTransfer}},
  year   = {2010},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-6026-invite-2xx-transactions},
  note   = {IETF / RFC Editor, accessed 2026-09-25}
}