System information

Conclusion
This chapter discussed many aspects of device state handling in Asterisk. We started
by discussing the core concepts of device states and extension states, and built up from
there. We covered how SIP phones can subscribe to states, tools for creating custom
states, and two mechanisms that can be used for distributing states among many serv-
ers. Finally, we covered one of the features in Asterisk, Shared Line Appearances, that
relies heavily on the device state infrastructure in Asterisk to operate.
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