14.2. Extension States

Extension states are another important concept in Asterisk. Extension states are what SIP devices subscribe to for presence information. (SIP presence is discussed in more detail in Section 14.3). The state of an extension is determined by checking the state of one or more devices. The list of devices that map to extension states is defined in the Asterisk dialplan, /etc/asterisk/extensions.conf, using a special hint directive. Figure 14-2 shows the mapping between devices, device states, and extension states.

Figure 14-2. Extension state mappings