Source note · Call transfer semantics REFER and Replaces
The Replaces header field identifies an existing dialog by Call-ID, to-tag and from-tag, and a user agent server matches those parameters as if they were tags in an incoming request, comparing the to-tag parameter to its own local tag and the from-tag parameter to the remote tag.
Checked 2026-09-16
In other words, the to-tag parameter is compared to the local tag, and the from-tag parameter is compared to the remote tag.
- Vendor
- IETF
- Product
- Session Initiation Protocol
- Subsystem
- Replaces
- Deployment
- not restricted
- Region
- not restricted
- Release range
- Standards Track
- Checked
- 2026-09-16
Sources
- RFC 3891 — The Session Initiation Protocol (SIP) "Replaces" Header — IETF / RFC Editor · tier 1 standards and regulators · RFC 3891 section 3, first 2 paragraphs
Cite this note
APA
WarmTransfer. (2026, September 16). Call transfer semantics REFER and Replaces: source note xfersem-replaces-matches-on-three-values. WarmTransfer. https://warmtransfer.net/knowledge/claims/xfersem-replaces-matches-on-three-values
BibTeX
@misc{warmtransfer-claim-xfersem-replaces-matches-on-three-values,
title = {Call transfer semantics REFER and Replaces: source note xfersem-replaces-matches-on-three-values},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/xfersem-replaces-matches-on-three-values},
note = {Source note xfersem-replaces-matches-on-three-values, checked 2026-09-16}
}