Indicating Fax over IP Capability in the Session Initiation Protocol (SIP)

Publisher

IETF RFC Editor

URL

https://www.rfc-editor.org/rfc/rfc6913.html

Published

2013-03-01

Updated

unknown

Accessed

2026-09-24

HTTP status

200

License

IETF Trust Legal Provisions; RFC text may be reproduced under IETF Trust terms; store short excerpts and locators only

Source notes citing this source

• RFC 6913 says a calling user agent placing a fax call SHOULD include the sip.fax media feature tag in the Accept-Contact header of the INVITE. in context
• RFC 6913 defines the sip.fax media feature tag with values t38 (fax will use ITU-T T.38) and passthrough (fax will be carried in G.711). in context
• 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. in context
• RFC 6913 defines the sip.fax media feature tag with values t38 and passthrough so SIP user agents can advertise fax capability in REGISTER and callers can request it with Accept-Contact in INVITE. in context
• RFC 6913 motivates the sip.fax tag by noting that fax calls are treated as voice calls until after they are connected which can route them to non-fax endpoints. in context

Cite this source record

APA

WarmTransfer. (2013, March 1). Indicating Fax over IP Capability in the Session Initiation Protocol (SIP). WarmTransfer. https://warmtransfer.net/knowledge/sources/rfc-6913-sip-fax-indication

BibTeX

@misc{warmtransfer-rfc-6913-sip-fax-indication,
  title  = {Indicating Fax over IP Capability in the Session Initiation Protocol (SIP)},
  author = {{WarmTransfer}},
  year   = {2013},
  url    = {https://warmtransfer.net/knowledge/sources/rfc-6913-sip-fax-indication},
  note   = {IETF RFC Editor, accessed 2026-09-24}
}