June 2005
Intermediate to advanced
502 pages
21h 48m
English
Content preview from Switching to VoIP
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Asterisk Channels
|
417
; zapata.conf
switchtype=national
context=default
signalling=pri_cpe
group=1
callerid=1-800-534-1550
channel => 1-23
zaptel.conf sets up a T1 span, configures the 24 DS0 channels on the T1, and sets the
framing and coding. Then zapata.conf configures the telephony apparatus for those
channels: national PRI signaling, a custom caller ID string, and the default dial-plan
context. The channels are grouped into a single rollover group (
1). Finally, on the
last line, these settings are applied to Zaptel channels 1 through 23. Within the dial-
plan, these channels will be referenced as
Zap/1, Zap/2, and so on.
E1 circuits will have 31 bearer channels and typically use HDB3 cod-
ing instead of B8ZS. Keep that in mind if you’re working outside
North America.
SIP Channels
Asterisk implements SIP only partially. Though SIP itself describes a total PBX
replacement approach using VoIP, Asterisk employs SIP mainly for connecting IP
phones and for trunking to other systems that also use SIP—like Zaptel. Asterisk
deals with its SIP subsystem in terms of channels: legs of a call. Two channels are
needed to complete a call between two SIP phones. A call between an analog phone
and a SIP phone also requires two channels: one Zaptel channel and one SIP channel.
Asterisk refers to devices
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.