PDF of this tutorialOne feature of most messaging systems is some form of presence awareness. At the most rudimentary level, presence awareness lets users know when other users, particularly those on their contact lists, are on-line and willing to accept messages. But when the IM system is part of an integrated communications platform, presence awareness can become more sophisticated. It can notify others when a user is on-line, willing to accept phone calls at a home or office number or has a mobile phone turned on. Users can even set presence messages so others trying to contact them will know that they've stepped out for lunch and will return at a certain time. When the element of mobility is added to IM, it introduces a new level of presence awareness, letting others know where a user is based on where the user logs into the system or location information provided by the wireless network. For example, if User A wanted to set a meeting with User B but noticed when accessing the messaging system that User B was out of town, User A wouldn't even have to contact User B to learn that the user was unavailable.
This level of presence awareness does bring up issues, particularly that of privacy. Just as even the basic messaging systems of today allow users to make themselves invisible to other users when they are on-line or to block communication from certain users, more advanced messaging systems will have to provide a certain degree of control over presence awareness. Only the most trusted users would have access to location information, for example, so users wouldn't be broadcasting to the world at large that they're away from home. There can be certain degrees of presence information made available, from appearing totally invisible on-line to complete strangers to "away from the office" messages to business colleagues and full presence information to immediate family.
