Hi Craig,
 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.
 CF> T1 is most-of-all a bit-rate and electrical specification, and is
 CF> typically delivered on two pair (one transmit and one receive). It's a
 CF> base data rate of 1.544 Mbits that is broken into 8000 frames per second
 CF> of 193 bits. Of those 1 is framing, and the other 192 are data. Things
 CF> get a bit confusing thereon because there are a lot of options, one 
eing
 CF> the framing format used. For example, it could be the format expected by
 CF> a D4 channel bank (which is fairly common).
 CF> In D4 framing, the 192 bits are divided into 24 8-bit channels, designed
 CF> to carry voice signals. Twelve of these frames are grouped together
 CF> logically into a super-frame, and in the 6th and 12th frames of the
 CF> super-frame the LSB of each channel is dropped and becomes a signalling
 CF> bit (called "A" and "B"). These correspond to E & M on some trunks, or 
n
 CF> other circuits they indicate loop status. Because of the robbed bits in
 CF> this format, you can't use all 8 bits all the time. The result is that
 CF> data circuits that share a T-1 with D4 channels can only be 56,000 bits
 CF> per second. Another popular framing format is Extended-Super-Frame, 
hich
 CF> is similar to D4, but the superframes are 24 frames long with 4
 CF> signalling bits.
 CF> Neither apprecialy affects analog modem performance.
Isn't there a digital/analog conversion each time it goes thru the channel 
bank resulting in further loss?
fdrennon@pobox.com
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