\begin{abstract}
Fax over IP is currently using SMTP, i.e.  the fax is sent as an e-mail. 
It would be desireable to support a fax delivery that can return status
of the transmission in real time, such as whether the phone number or
address was correct, whether the remote side was busy, etc.  The ITU is
standardizing a protocol for transferring real time fax over IP, T.38. 
This standard is meant to be used with the H.323 standard, but it is
also possible to use it together with SIP, provided that SDP is extended
to support the necessary parameters.  This document defines extensions
to SDP to support the use of T.38 for real-time fax.
\end{abstract}
