Source note · Call transfer semantics REFER and Replaces
Without Referred-By a Transfer Target has no definitive information about which party initiated the transfer or in some cases that a transfer is taking place at all; the simplest and least secure use is a Referred-By header field in the REFER that is copied into the triggered INVITE, and the more secure form is a security token generated and signed by the Transferor and carried in a message body through the Transferee to the Target.
Checked 2026-09-16
- Vendor
- IETF
- Product
- Session Initiation Protocol
- Subsystem
- Referred-By
- Deployment
- not restricted
- Region
- not restricted
- Release range
- BCP 149
- Checked
- 2026-09-16
Sources
- RFC 5589 — Session Initiation Protocol (SIP) Call Control - Transfer — IETF / RFC Editor · tier 1 standards and regulators · RFC 5589 section 8 Transfer with Referred-By
Cite this note
APA
WarmTransfer. (2026, September 16). Call transfer semantics REFER and Replaces: source note xfersem-referred-by-tells-the-target-who-transferred. WarmTransfer. https://warmtransfer.net/knowledge/claims/xfersem-referred-by-tells-the-target-who-transferred
BibTeX
@misc{warmtransfer-claim-xfersem-referred-by-tells-the-target-who-transferred,
title = {Call transfer semantics REFER and Replaces: source note xfersem-referred-by-tells-the-target-who-transferred},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/xfersem-referred-by-tells-the-target-who-transferred},
note = {Source note xfersem-referred-by-tells-the-target-who-transferred, checked 2026-09-16}
}