Overview

Asterisk 11 has been outfitted with support for presence states. An easy way to understand this is to compare presence state support to the device state support Asterisk has always had. Like with device state support, Asterisk has a core API so that modules can register themselves as presence state providers, alert others to changes in presence state, and query the presence state of others. The difference between the device and presence state concepts is made clear by understanding the subject of state for each concept.

• Device state reflects the current state of a physical device connected to Asterisk
• Presence state reflects the current state of the user of the device

For example, a device may currently be not in use but the person is away. This can be a critical detail when determining the availability of the person.

Differences Between Presence State and Device State Support

While the architectures of presence state and device state support in Asterisk are similar, there are some key differences between the two.

• Asterisk cannot infer presence state changes the same way it can device state changes. For instance, when a SIP endpoint is on a call, Asterisk can infer that the device is being used and report the device state as in use. Asterisk cannot infer whether a user of such a device does not wish to be disturbed or would rather chat, though. Thus, all presence state changes have to be manually enacted.
• Asterisk does not take presence into consideration when determining availability of a device. For instance, members of a queue whose device state is busy will not be called; however, if that member's device is not in use but his presence is away then Asterisk will still attempt to call the queue member.
• Asterisk cannot aggregate multiple presence states into a single combined state. Multiple device states can be listed in an extension's hint priority to have a combined state reported. Presence state support in Asterisk lacks this concept.