\section*{Changes in Version -05}

Since version -04, the following changes have been made. 

\begin{itemize}

\item Local part of \header{Call-ID} needs to be cryptographically
random.

\item Added \header{Response-Key}, \header{Encryption}, \header{Hide}
and ``pgp'' authentication method. 

\item Removed \header{Public}, following the revised HTTP/1.1
\cite{draft-ietf-http-v11-spec-rev}; \header{Allow} can do the same
thing.

\item Updated phone URLs to \cite{draft-antti-telephony-url}.

\item \header{Proxy-Require} header added, as in RTSP.

\item ``Emergency'' priority value added.

\item 381 (Ambiguous) status code added.

\item Sequence numbers should be contiguous to allow loss detection.
Limited to 64 bits to allow numerical computations.

\item The service definitions have been moved to a separate document.

\item The \header{Also} header field and \header{Location} parameters have
moved to a separate document.

\item \header{Call-ID} defined consistently, with behavior for several
calls with the same Call-ID and several calls with different
\header{Call-IDs} for the same conference. 

\item {\sf UNREGISTER} was removed since {\REGISTER} with an expiration
time of zero accomplishes the same thing.

\item \header{Max-Forwards} header and status 483 added.

\item The default port number 5060 has been assigned to SIP.  The
address 224.0.1.75 also has been assigned as the ``all SIP servers''
multicast address.

\item Added table with list of headers used by each SIP server/client
type.

\item \header{CSeq} mandatory for requests and minimal implementations.

\item Proxy search rules made more precise.

\item Added ability of (state-ful) proxies to request to see {\BYE} and
{\ACK} packets via \header{Record-Route} and \header{Route}.

\item Retransmission timer for {\INVITE} changed to $T3$ = 30 seconds to
avoid multiple {\INVITE}s for a typical phone call.

\item {\ACK}s may contain session descriptions.

\item \header{signed-by} parameter added to \header{Authorization} header.

\item {\INVITE} and {\ACK} requests may also contain \header{Location}
so that the callee can send the {\BYE} directly.

\item {\OPTIONS} allowed to return current status such as Busy or Decline.

\item Unicast example clarified.

\item Added section on SDP usage for unicast. Currently, require
``lining up'' media types.

\item Tentatively added {\CANCEL} request to terminate searches.

%\item Status code 484 (Duplicate Request) added.
% dangerous if route changes; shelved for now

\item Status 181: Call Is Being Forwarded.

\item \header{Content-Encoding} for compressed payloads.

\item \header{Retry-After} may be used for {\REGISTER}.

\item \header{ETag}, \header{If-Match}, \header{If-None-Match}

\item Added \header{method} to \header{CSeq} response header.

\item Folded in Yaron Goland's ``nit'' comments: URL phone now conforms
to ``URLs for Telephony'' I-D; production of password; port number;
short SIP URLs removed [controversial?]. 

\item Cleaned up \header{From}, \header{To}, \header{Request-URI}
throughout spec to always include full SIP URL.  (Otherwise, there is an
ambiguity with users named ``sip'', since the user name can contain a
colon.  Search Four11 if you don't believe that the name exists\ldots)

\item Warning header syntax fixed to allow 606.3.

\item \header{signed-by} can be general URI.  However, not clear yet
whether URI schemes are the most appropriate mechanism to denote a
principal.  In X.509 certificates, email addresses are used.

\end{itemize}
