Source note · Call transfer semantics REFER and Replaces
Where a Replaces header field matches a dialog that has already terminated the user agent should decline the request with a 603 Declined, and RFC 3891 gives the reason: a 600-class response prevents an irritating race condition in which the user agent rings or alerts for a replacement call that is no longer wanted.
Checked 2026-09-16
If the Replaces header field matches a dialog which has already terminated, the UA SHOULD decline the request with a 603 Declined response.
- 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, paragraph 7
Cite this note
APA
WarmTransfer. (2026, September 16). Call transfer semantics REFER and Replaces: source note xfersem-replaces-603-on-a-dead-dialog. WarmTransfer. https://warmtransfer.net/knowledge/claims/xfersem-replaces-603-on-a-dead-dialog
BibTeX
@misc{warmtransfer-claim-xfersem-replaces-603-on-a-dead-dialog,
title = {Call transfer semantics REFER and Replaces: source note xfersem-replaces-603-on-a-dead-dialog},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/xfersem-replaces-603-on-a-dead-dialog},
note = {Source note xfersem-replaces-603-on-a-dead-dialog, checked 2026-09-16}
}