System information
The Zapata Telephony Project originally produced a T1 card, the Tormenta, that is the
ancestor of most Asterisk-compatible T1 cards. The original Tormenta cards are now
considered obsolete, but they do still work with Asterisk.
Digium makes several different digital circuit interface cards. The features on the cards
are the same; the primary differences are whether they provide T1 or E1 interfaces, and
how many spans each card provides. Digium has been producing DAHDI cards for
Linux longer than anyone else; it was deeply involved with the development of DAHDI
(formerly Zaptel) on Linux, and has been the driving force behind DAHDI development
over the years.
Sangoma, which has been producing open source WAN cards for many years, added
Asterisk support for its T1/E1 cards a few years ago.
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Rhino has had T1 hardware for
Asterisk for a while now, and there are many other companies that offer digital interface
cards for Asterisk as well.
Channel banks
A channel bank is loosely defined as a device that allows a digital circuit to be de-
multiplexed into several analog circuits (and vice versa). More specifically, a channel
bank lets you connect analog telephones and lines into a system across a T1 line.
Figure C-2 shows how a channel bank fits into a typical office phone system.
Figure C-2. One way you might connect a channel bank
Although they can be expensive to purchase, many people feel very strongly that the
only proper way to integrate analog circuits and devices into Asterisk is through a
channel bank. Whether that is true or not depends on a lot of factors, but if you have
the budget, they can be very useful.
#
You can often pick up used channel banks on
‖ It should be noted that a Sangoma Frame Relay card played a role in the original development of Asterisk
(see http://linuxdevices.com/articles/AT8678310302.html); Sangoma has a long history of supporting open
source WAN interfaces with Linux.
#We use channel banks to simulate a central office. One 24-port channel bank off an Asterisk system can
provide up to 24 analog lines—perfect for a classroom or lab.
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