[Asterisk-doc] Connecting to a PRI

[Gene Naden]

My earlier writing omitted mention of E-1. I have written a few paragraphs
to try to remedy it. Would the interested persons please have a look at it
and criticize, especially
folks familiar with E1.

Gene Naden, MA
Programmer Analyst
GlobalTeldata II, LLC
4700 N. Ravenswood
Chicago, IL 60640
(773) 878-3161 x 223
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T-1 AND E-1
In the context of Asterisk, T-1 and E-1 are digital telephony schemes 
that multiplex a number of voice channels onto one line. E-1 is used 
mainly in Europe and Asia, while T-1 is used in the United States and
Canada. In either case, signaling and framing information must be 
carried, either within the voice channels or in separate, non-voice 
channels. There are various signallng and framing schemes. 

One signaling scheme that is used with Asterisk for T-1 connections 
is ISDN PRI (Integrated Services Digital Network, Primary 
Rate Interface.) With IDSN PRI, a T-1 connection has 24 channels. 
In the context of Asterisk, channels 1-23 carry voice and are referred 
to as "B" (bearer) channels. Channel 24 carries signaling information 
and is referred to as a "D" (data) channel.

ISDN PRI signaling is also used for E-1 connections. Such an E-1
connection has 31 channels. For Asterisk, channels 1-15 and 17-31 carry 
voice and are called "B" channels, while channel 16 carries signaling 
information and is called the "D" channel. Channel zero is used for 
framing.