Source note · Troubleshooting fax over IP failures
RFC 6913 describes that SIP fax calls are normally set up as voice calls and switched to T.38 only after answer, so they can be routed to user agents that are not fax capable.
Checked 2026-10-02
- Vendor
- not restricted
- Product
- not restricted
- Subsystem
- SIP fax capability
- Deployment
- any
- Region
- not restricted
- Release range
- RFC 6913, March 2013
- Checked
- 2026-10-02
Sources
- Indicating Fax over IP Capability in the Session Initiation Protocol (SIP) — IETF RFC Editor · tier 1 standards and regulators · Abstract and Section 1 (Introduction)
Cite this note
APA
WarmTransfer. (2026, October 2). Troubleshooting fax over IP failures: source note fax-over-ip-troubleshooting-rfc6913-voice-first. WarmTransfer. https://warmtransfer.net/knowledge/claims/fax-over-ip-troubleshooting-rfc6913-voice-first
BibTeX
@misc{warmtransfer-claim-fax-over-ip-troubleshooting-rfc6913-voice-first,
title = {Troubleshooting fax over IP failures: source note fax-over-ip-troubleshooting-rfc6913-voice-first},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/fax-over-ip-troubleshooting-rfc6913-voice-first},
note = {Source note fax-over-ip-troubleshooting-rfc6913-voice-first, checked 2026-10-02}
}