Source note · Early media and ringback behavior

Under RFC 3262, if the initial INVITE carries the 100rel option tag in a Require header, the UAS must send every non-100 provisional response reliably. In a Supported header the tag only signals capability.

Checked 2026-09-24

Vendor: IETF
Product: SIP
Subsystem: reliable provisional responses
Deployment: any
Region: not restricted
Release range: RFC 3262
Checked: 2026-09-24

Sources

RFC 3262: Reliability of Provisional Responses in the Session Initiation Protocol (SIP) — IETF / RFC Editor · tier 1 standards and regulators · Sections 3 and 4 (UAS and UAC behavior)

Cite this note

APA

WarmTransfer. (2026, September 24). Early media and ringback behavior: source note early-media-ringback-100rel-require. WarmTransfer. https://warmtransfer.net/knowledge/claims/early-media-ringback-100rel-require

BibTeX

@misc{warmtransfer-claim-early-media-ringback-100rel-require,
  title  = {Early media and ringback behavior: source note early-media-ringback-100rel-require},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/claims/early-media-ringback-100rel-require},
  note   = {Source note early-media-ringback-100rel-require, checked 2026-09-24}
}

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