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\title{Automatic Configuration for SIP User Agents}
\author{Schulzrinne}
\shorttitle{SIP Proxy}
\filename{ietf-mmusic-sip-proxy-00}
\wg{MMUSIC WG}
\address{Columbia U.}
\pubdate{\today}
\expires{May 1999}

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\begin{document}
\maketitle
\begin{abstract}
This note defines one mechanism by which SIP user agents can determine
if they need to use a near-end proxy for outgoing requests.
\end{abstract}

\section{Proxy Configuration}

It is desirable that SIP \cite{draft-ietf-mmusic-sip} user agents should
need a minimum amount of configuration.  In particular, SIP user agents
implemented in embedded systems may not have any permanent storage. 
There exist mechanisms within SIP for the registrar to set the
\header{Organization} and \header{Date} header for future SIP requests. 
Currently, there is no mechanism for automatically configuring whether
the SIP user agent uses a near-end proxy for outgoing requests or
whether it contacts the destination address directly via DNS.  In some
network configurations, near-end proxies are necessary for setting up or
traversing firewalls, for example. 

\begin{syntax}
Use-Proxy & = & 
\end{syntax}

\section{Display Name and User Name}

\section{Security Considerations}

SIP user agents {\SHOULD} ascertain that the proxy indicated by the
\header{Use-Proxy} header field can be trusted.  This can be
accomplished by insisting on a signed response.  In some environments,
it may be sufficient to only accept proxies in the same subnet or
network as the UA. 

\section{Author Address}

\begin{flushleft}
Henning Schulzrinne\\
Dept. of Computer Science\\
Columbia University\\
1214 Amsterdam Avenue\\
New York, NY 10027\\
USA\\
electronic mail: {\sf schulzrinne@cs.columbia.edu}
\end{flushleft}

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