\section{Changes in Version -09}

Since version -08, the following changes have been made. 

\begin{itemize}
\item Checked and capitalized or rewrote ``may'', ``should'' and
``must''.

\item Consistent use of ``header field'' throughout the spec.

\item Warning messages updated.

\item Added \header{method} URL parameter that indicates request method.
Now allows complete construction of SIP request from within a web page
and a \header{Location} header. The latter is particularly useful for
third-party call control.

\item Clarified use of SRV DNS records. TCP and UDP may have equal
priority, but different weight.

\item Added 486 (Busy here) status hen there might be other branches,
such as answering machines, ready to take the call.

\item Added \header{expires} parameter to \header{Location} header field
to allow reporting of expiration times for each location.

\item Clarified 481 as referring to a mismatch in describing a call leg
({\BYE}) or transaction ({\CANCEL}).

\item Clarified that the \header{CSeq} method in the request is always
the same as the request method, even for {\ACK}.

\item Made the \header{tag} parameter a \header{To} or \header{From}
parameter, not a URL parameter.  Tags may be needed for some non-SIP
URIs.

\item \header{Location} header field renamed to \header{Contact}, with
syntax according to \header{To} and \header{From}. 

\item Rules for defaults in \header{Contact} headers now simply point to
URL rules.

\item Added wording to {\ACK} section on how to process requests.

\item Made all elements in \header{sent-protocol} mandatory to avoid
ambiguity of whether ``SIP/2.0'' referes to the default protocol of
version ``SIP'' with transport ``2.0'' or the correct interpretation.

\item Filled in descriptions of status codes 410, 411 and 413, basically
unchanged from HTTP.

\item Made \header{Record-Route} and \header{Route} header fields
consistent with \header{From}, \header{To}, \header{Contact}. As long as
the URI doesn't contain parameters or commas, this is no change, but it
avoids the same problems that lead to the change in \header{Contact}
syntax.

\item Added remark to SDP section to use a zero address to temporarily
disable media transmission (``put call on hold'').

\item Changed wording for \header{Record-Route} to apply to any
subsequent request.

\end{itemize}
