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Asterisk Channels

Almost nothing happens in Asterisk without a channel being involved. A channel is an entity inside Asterisk that acts as a channel of communication between Asterisk and another device. That is, a phone, a PBX, another Asterisk system, or even Asterisk itself (in the case of a local channel).

Our documentation and many Asterisk users speak about channels in terms of "calls". A call can be one or more channels creating a path of communication or activity through the Asterisk system.

To give you an idea about what channels do, here are a few facts about them:

  • Channel Drivers provide channels in Asterisk.
  • Channels can interface with each other through bridges.
  • Applications and functions can affect the state or attributes of a channel or its media stream.
  • Channels are commonly passing audio between communication endpoints, but can pass other data, such as video or text messages.
  • Channels execute instructions with dialplan, but can be controlled by other APIs (AGI,AMI,ARI) or interfaces (CLI). 

Common Asterisk Channels

One of the many benefits of Asterisk is the capability to interface with as many different technologies as you have channel drivers! However, most administrators will only make use of a few types at a time.

Here are a few commonly used channel types:

SIP channels are used to interface with SIP capable VOIP devices, such as phones, channel banks, other PBXs or Internet Telephony Service Providers.

DAHDI channels are used to interface with DAHDI drivers and PRI libraries. In this case chan_dahdi allows you to use any DAHDI capable devices, such as Digium's line of T1/E1/J1 interface cards.

Local channels are used for dialing inward to the system itself, allowing any Asterisk component that can dial to call directly into dialplan. This provides a sort of "fake" call that still executes real instructions.

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Configuring Channels

Text File Configuration

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