Source note · Call transfer semantics REFER and Replaces

The early-only parameter in a Replaces header field restricts the replacement to an early dialog, and where it is present and the header matches a confirmed dialog the user agent rejects the request with a 486 Busy response.

Checked 2026-09-16

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 sections 3 and 4, early-only

Cite this note

APA

WarmTransfer. (2026, September 16). Call transfer semantics REFER and Replaces: source note xfersem-replaces-early-only-gets-486. WarmTransfer. https://warmtransfer.net/knowledge/claims/xfersem-replaces-early-only-gets-486

BibTeX

@misc{warmtransfer-claim-xfersem-replaces-early-only-gets-486,
  title  = {Call transfer semantics REFER and Replaces: source note xfersem-replaces-early-only-gets-486},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/claims/xfersem-replaces-early-only-gets-486},
  note   = {Source note xfersem-replaces-early-only-gets-486, checked 2026-09-16}
}

Read in context