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45 lines
2.0 KiB
Plaintext
45 lines
2.0 KiB
Plaintext
Implementing a Channel
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======================
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* What is a channel?
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A channel is a unit which brings in a call to the Asterisk PBX. A channel
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could be connected to a real telephone (like the Internet Phone Jack) or
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to a logical call (like an Internet phone call). Asterisk makes no
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distinction between "FXO" and "FXS" style channels (that is, it doesn't
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distinguish between telephone lines and telephones).
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Every call is placed or received on a distinct channel. Asterisk uses a
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channel driver (typically named chan_xxx.so) to support each type of
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hardware.
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* What do I need to create a channel?
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In order to support a new piece of hardware you need to write a channel
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driver. The easiest way to do so is to look at an existing channel driver
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and model your own code after it.
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* What's the general architecture?
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Typically, a channel reads a configuration file on startup which tells it
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something about the hardware it's going to be servicing. Then, it
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launches a thread which monitors all the idle channels (See the chan_modem
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or the chan_ixj for an example of this). When a "RING" or equivalent is
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detected, the monitoring thread should allocate a channel structure and
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assign all the callbacks to it (see ixj_new, for example), and then call
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ast_pbx_start on that channel. ast_pbx_start will launch a new thread to
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handle the channel as long as the call is up, so once pbx_start has
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successfully been run, the monitor should no longer monitor that channel.
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The PBX thread will use the channel, reading, writing, calling, etc., and
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multiplexing that channel with others using select() on the channel's
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file descriptor (if your channel doesn't have an associated file
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descriptor, you'll need to emulate one somehow, perhaps along the lines of
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what the translator API does with its channel.
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When the PBX is finished with the line, it will hang up the line, at which
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point it the hardware should again be monitored by the monitoring thread.
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---------------
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For more information, please consult the Asterisk Developer's Documentation
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on http://www.asterisk.org
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