[Asterisk-Users] offtopic - channel banks

[Chris A. Icide]

Ilia,

Think of a channel bank as a concentrator.  In a single T1 channel bank, 
you concentrate 24 analog two wire phone connections into a single 4 wire 
digital interface.

So in your case, the RJ45 connector is for the T1 interface to Asterisk, 
the local CLEC, or whatever you intend to connect it to.  On the T1 side, 
there has to be several layers of signalling and encoding.  Alot of this 
information is superfluous, but may help you when it comes to understanding 
your configs.

Before we even talk about E&M signalling, you have the T1 framing and 
encoding.  This is used to allow both ends of the T1 circuit to understand 
how the 24 channels are being configured on the 4 wire circuit.  It's 
generally going to be either sf, d4 or esf, b8zs.  This is known as the 
framing and encoding.

Once those are agreed upon, then we need to set up the way the T1 is going 
to signal across the channels.  Normal phone lines (analog) use voltages, 
resistances, and dtmf to signal what it is doing.  Since a T1 is a digital 
circuit we can't do that, so we need to set up another way to signal, so 
that the channel bank knows what to do when we send some kind of digital 
signal.  In this case, this is the E&M signalling you asked about.

Finally, you probably are looking for some way to plug your phone's RJ11 
connecter into the channel bank.  Unfortunately it's not that easy.  That 
big Centronics style connecter is where you actually have to plug up the 
phone.  there are 24 pairs of contacts in that connecter that are 
associated with each channel on the T1 circuit.  Historically, you would 
connect up a cable of 50 conductors connected to the centronics connector 
on one end, and then to one side a punch down block on the other (just a 
quick-connect style access device for copper wire).  On the other side of 
the punch down block, you would connect the wires that would then run to 
the remote wall jacks, etc. where your phones plug in.

The problem you have is wither by google mastery or just plain brute force 
testing, you need to figure out the pinout of that centronics port before 
you can connect up any phones successfully.

-Chris

On 10:56 PM 9/5/2004, Ilia Mirkin wrote:
 >While I understand everything that you have said, I'm still a little
 >confused. Yes - I have what looks like a centronics connector on the
 >back. So, I can do "t100p with e&m signalling" <-> "act-1241 e&m card"
 ><-> what? Namely, if the E&M card deals with the T1 end of the channel,
 >how do I get that to a real phone? Will it "just work" if I plug an
 >analog phone onto the correct pair coming out of the connector in the
 >back? If not, what is the output of the E&M card? (and, more
 >importantly, what would I need to do to hook it up to an analog phone?)
 >
 >Thanks for clearing things up.
 >
 >---
 >Ilia Mirkin
 >imirkin at mit.edu
 >
 >On Sun, 2004-09-05 at 04:31, Steven Critchfield wrote:
 >> On Sun, 2004-09-05 at 03:10, Ilia Mirkin wrote:
 >> > hi,
 >> >
 >> > i have some newbie questions about channel banks. i have an adtran
 >> > act-1241 sitting around. it accepts D4 modules, and it contains a number
 >> > of e&m cards.
 >> >
 >> > first of all, how does this thing work? a t1 contains 24 channels, and i
 >> > noticed that the channel bank has space for 24 cards. what do these
 >> > cards do? what are their outputs? the ones that are in there have some
 >> > outputs on the front marked "test", but nothing else. there are a number
 >> > of wires coming out the back (48, if i had to guess), and it has a few
 >> > ports on the front which seem to be able to take in a T1. am i correct
 >> > in understanding that it is the card in the bank that determines the
 >> > signalling style, and not the t1? as such, is there no way that i could
 >> > use it in its current configuration to have it talk with analog phones
 >> > (i.e. something like t100p -> act-1241 with e&m cards -> phone)? i'm a
 >> > bit unclear on the different signalling types, and their
 >> > intercompatibilities.
 >> >
 >> > if anyone could shed any light into this, i would very much appreciate
 >> > it.
 >>
 >> Think of the T1 as 24 digital digital pathways. The coding of each
 >> pathway must be compatible on each end. With E&M cards, you signal with
 >> E&M and the line will work. The cards plug into a backplane where the
 >> controller routes the digital signal to the card and then optionally
 >> hook up the output from the card to a connector that consolidates many
 >> lines. Look for something that looks like an older 50 pin scsi D
 >> connector.
 >>
 >> If there is 2 RJ45 jacks on the front, and 2 50 pin D connectors on the
 >> back, then it is likely that each card controlls 2 lines each. If there
 >> is only 1 50 pin connector, then there is only 24 channels.
 >>
 >> Hope that helps.
 >
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