\section{IANA Considerations}

Section~\ref{sec:option_tags} describes a name space and mechanism for
registering SIP options.  Section~\ref{sec:Warning} describes the name
space for registering SIP \header{warn-codes}. 

SIP Header field names are registered with IANA.  They do not require
working group or working group chair review, but {\SHOULD} be documented
in an RFC or Internet draft. For Internet drafts, IANA is requested to
make the draft available as part of the registration database.

\motivation{By the time an RFC is published, colliding names may have
already been implemented.}

The following information needs to be provided to IANA in order to
register a new header name:

\begin{itemize}
\item The name and email address of the individual performing the
registration.
\item The name of the header field being registered.
\item A compact form version for that header field, if one is defined.
\item The name of the draft or RFC where the header is defined.
\item A copy of the draft or RFC where the header is defined.
\end{itemize}

SIP response status codes are registered with IANA. Because the status
code space is limited, they do require working group or working group chair
review, and {\MUST} be documented in an RFC or Internet draft. For
Internet drafts, IANA is requested to make the draft available as part
of the registration database.

The following information needs to be provided to IANA in order to
register a new response code:

\begin{itemize}
\item The name and email address of the individual performing the
registration.
\item The number of the response code being registered.
\item The default reason phrase for that status code.
\item The name of the draft or RFC where the status code is defined.
\item A copy of the draft or RFC where the status code is defined.
\end{itemize}

When a registration for either a new header or new status code is
created based on an I-D, and that I-D becomes an RFC, the person that
performed the registration {\MUST} notify IANA to change the
registration to point to the RFC instead of the Internet Draft.

Headers {\SHOULDNOT} use the \header{X-} prefix notation and {\MUSTNOT}
duplicate the names of headers used by SMTP or HTTP unless the syntax is
a compatible superset and the semantics are similar.  Some common and
widely used header fields {\MAY} be assigned one-letter compact forms
(Section~\ref{sec:compact}).  Compact forms can only be assigned after
SIP working group review.  In the absence of this working group, a
designated expert reviews the request.
