Source note · Early media and ringback behavior
RFC 3262 forbids sending 100 (Trying) reliably; only provisional responses numbered 101 to 199 may be sent reliably.
Checked 2026-09-24
A UAS MUST NOT attempt to send a 100 (Trying) response reliably.
- 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 · Section 3 (UAS Behavior)
Cite this note
APA
WarmTransfer. (2026, September 24). Early media and ringback behavior: source note early-media-ringback-100-not-reliable. WarmTransfer. https://warmtransfer.net/knowledge/claims/early-media-ringback-100-not-reliable
BibTeX
@misc{warmtransfer-claim-early-media-ringback-100-not-reliable,
title = {Early media and ringback behavior: source note early-media-ringback-100-not-reliable},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/early-media-ringback-100-not-reliable},
note = {Source note early-media-ringback-100-not-reliable, checked 2026-09-24}
}