Switching to VoIP

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The Asterisk CLI

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Inspecting Channels

There are several types of voice channels in Asterisk. There can be analog FXO (for-

eign exchange office) channels, such as those facilitated by a POTS telephone com-

pany line and an X100P card. There can also be voice channels provided by H.323,

SIP, IAX, SCCP, and MGCP (all different VoIP signaling protocols), as well as by

FXS (foreign exchange station) devices like QuickNet’s Phone Jack interface card

and PRI interfaces, too.

You can use the Asterisk CLI to inspect each type of channel, but the details pro-

vided are different for each:

•

zap show channels

• iax2 show channels

• sip show channels

Each of these commands provides a list of channel numbers that can correspond to a

numeric reference in the channel name, as described earlier (example:

Zap/1). Take a

look at a

zap show channels command:

pbx*CLI> zap show channels

Chan. Num. Extension Context Language MusicOnH

1 incoming default

The command output shows that there is a single Zaptel channel available for use by

the Asterisk PBX. In our experimental server, this logical channel represents the

physical X100P interface with a telco line connected to it. The command output tells

that the context for calls on this channel is

incoming because the start extension in

extensions.conf is established ...