Claim record · SIP transactions dialogs and call setup
Two requests reuse the branch and sequence number of the request they refer to by design: a cancellation must carry a single routing header matching the top one of the request being cancelled and the identical numeric part of the sequence header, and an acknowledgement of a non-2xx response must carry a routing header equal to the top one of the original request and the same sequence number with the method set to acknowledge.
fact · verified 2026-09-15
A CANCEL constructed by a client MUST have only a single Via header field value matching the top Via value in the request being cancelled.
- Vendor
- IETF
- Product
- Session Initiation Protocol
- Subsystem
- transactions
- Deployment
- not restricted
- Region
- not restricted
- Release range
- current as of 2026-09-15
- Status
- fact
- Confidence
- 0.90
- Verified
- 2026-09-15
Sources
- RFC 3261 — SIP: Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · RFC 3261 sections 9.1 and 17.1.1.3
Cite this claim
APA
WarmTransfer. (2026, September 15). SIP transactions dialogs and call setup: claim siptx-cancel-and-non-2xx-ack-reuse-the-branch. WarmTransfer. https://warmtransfer.net/knowledge/claims/siptx-cancel-and-non-2xx-ack-reuse-the-branch
BibTeX
@misc{warmtransfer-claim-siptx-cancel-and-non-2xx-ack-reuse-the-branch,
title = {SIP transactions dialogs and call setup: claim siptx-cancel-and-non-2xx-ack-reuse-the-branch},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/siptx-cancel-and-non-2xx-ack-reuse-the-branch},
note = {Claim siptx-cancel-and-non-2xx-ack-reuse-the-branch, verified 2026-09-15}
}