Presence information

Presence information has wide application in many communication services and is one of the innovations driving the popularity of instant messaging or recent implementations of voice over IP clients.

The most common use of presence today is to display an indicator icon on instant messaging clients, typically from a choice of graphic symbols with easy-to-convey meanings, and a list of corresponding text descriptions of each of the states.

Even when technically not the same, the "on-hook" or "off-hook" state of called telephone is an analogy, as long as the caller receives a distinctive tone indicating unavailability or availability.

The analogy with free/busy tone on PSTN is inexact, as the "on-hook" telephone status reflects the ability of the network to reach the recipient after the requester has initiated the conversation.

This idea is already familiar to instant messaging users who have their status set to "Away" (or equivalent) if their computer keyboard is inactive for some time.

Extension to other devices could include whether the user's cell phone is on, whether they are logged into their computer, or perhaps checking their electronic calendar to see if they are in a meeting or on vacation.

Basic versions of this idea are already common in instant messaging clients as a "Blocking" facility, where users can appear as unavailable to selected watchers.

Presence information allows you to instantly see who is available in your corporate network, giving more flexibility to set up short-term meetings and conference calls.

An example of the time-saving aspect of presence information is a driver with a GPS; he/she can be tracked and sent messages on upcoming traffic patterns that, in return, save time and money.

In 1999, a group called the Instant Message and Presence Protocol (IMPP) working group (WG), was formed within the Internet Engineering Task Force organization (IETF) in order to develop protocols and data formats for simple presence and instant messaging services.

In 2001, the SIMPLE working group was formed within IETF to develop a suite of CPP-compliant standards for presence and instant messaging applications over the Session Initiation Protocol (SIP).

The SIMPLE activity specifies extensions to the SIP protocol which deal with a publish and subscribe mechanism for presence information and sending instant messages.