\section{Scope}
\label{sec:scope}

This extension does not replace media negotiation mechanisms defined for
SIP (e.g.  SDP \citenorm{rfc2327}), therefore media negotiation (e.g.,
choice of voice and video codecs) {\MUST} be performed according to
\citenorm{rfc3264}.  This extension is only aimed to give the watchers
hints about the presentity's preferences, willingness and capabilities
to communicate before watchers initiate SIP-based communication with the
presentity.

