1. Introduction

   ENUM (E.164 Number Mapping, RFC 3761prop [1]) is a system that uses DNS
   (Domain Name Service, RFC 1034std13 [8]) to translate telephone numbers,
   such as +12025332600, into URIs (Uniform Resource Identifiers, RFC
   2396(-> 3986std66) [9]), such as pres:user@host.com.  ENUM exists primarily to
   facilitate the interconnection of systems that rely on telephone
   numbers with those that use URIs to identify resources.

   Presence is a service defined in RFC 2778 [2] that allows users of a
   communications service to monitor one another's availability and
   disposition in order to make decisions about communicating.  Presence
   information is highly dynamic and generally characterizes whether a
   user is online or offline, busy or idle, away from communications
   devices or nearby, and the like.

   The IETF has defined a generic URI used to identify a presence
   service for a particular resource: the 'pres' URI scheme (defined in
   CPP [4]).  This document describes an enumservice for advertising
   presence information associated with an E.164 number.