\subsection{Contact-Type Element}
\label{sec:contact-type}

The \xmlelement{contacttype} element describes the type of the tuple. 
A tuple can represent a communication facility (``device''), a
face-to-face communication tuple (``in-person''), a set of devices
offering a common service (``service''), or a whole presentity
(``presentity'').  Additional types can be registered with IANA.

\motivation{URI schema are insufficient to distinguish the different
types of tuples.  For example, a SIP URI can designate a single device,
a presentity or a subgroup of devices.}
