Bob Morton wrote the following to Patrick Moore, and I quote (in part):
   PM> It depends on how it is done.  Technically you can have T1
   PM> service (24 64k channels ... 24 high grade voice good for 
   PM> 33.6k+ or 56k IDSN (8k used for telco network overhead)) over
   PM> a copper pair.
 BM> I thought T1 was implemented over TWO pairs...at least it is here. 
 BM> Also, I was told by a communications engineer that channel banking
 BM> a T1 into analog modems usually results in successful bps rates
 BM> well below 28.8k...like 14.4 - 19.2 reliably.
T1 is most-of-all a bit-rate and electrical specification, and is typically 
delivered on two pair (one transmit and one receive). It's a base data rate 
of 1.544 Mbits that is broken into 8000 frames per second of 193 bits. Of 
those 1 is framing, and the other 192 are data. Things get a bit confusing 
thereon because there are a lot of options, one being the framing format 
used. For example, it could be the format expected by a D4 channel bank 
(which is fairly common).              
                                                                        
In D4 framing, the 192 bits are divided into 24 8-bit channels, designed to 
carry voice signals. Twelve of these frames are grouped together logically 
into a super-frame, and in the 6th and 12th frames of the super-frame the LSB 
of each channel is dropped and becomes a signalling bit (called "A" and "B"). 
These correspond to E & M on some trunks, or on other circuits they indicate 
loop status. Because of the robbed bits in this format, you can't use all 8 
bits all the time. The result is that data circuits that share a T-1 with D4  
 channels can only be 56,000 bits per second. Another popular framing format 
is Extended-Super-Frame, which is similar to D4, but the superframes are 24
frames long with 4 signalling bits.       
Neither apprecialy affects analog modem performance.
Regards....
Craig
aka: cford@ix.netcom.com
--- timEd/2 1.10+
---------------