Source note · SIP transactions dialogs and call setup
A branch identifier written by an implementation of this specification must begin with the 7 characters z9hG4bK so that a server can tell it was constructed to this specification.
Checked 2026-09-15
The branch ID inserted by an element compliant with this specification MUST always begin with the characters z9hG4bK.
- Vendor
- IETF
- Product
- Session Initiation Protocol
- Subsystem
- transactions
- Deployment
- not restricted
- Region
- not restricted
- Release range
- current as of 2026-09-15
- Checked
- 2026-09-15
Sources
- RFC 3261 — SIP: Session Initiation Protocol — IETF / RFC Editor · tier 1 standards and regulators · RFC 3261 section 8.1.1.7
Cite this note
APA
WarmTransfer. (2026, September 15). SIP transactions dialogs and call setup: source note siptx-branch-carries-a-magic-cookie. WarmTransfer. https://warmtransfer.net/knowledge/claims/siptx-branch-carries-a-magic-cookie
BibTeX
@misc{warmtransfer-claim-siptx-branch-carries-a-magic-cookie,
title = {SIP transactions dialogs and call setup: source note siptx-branch-carries-a-magic-cookie},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/siptx-branch-carries-a-magic-cookie},
note = {Source note siptx-branch-carries-a-magic-cookie, checked 2026-09-15}
}