Fast File Transfer

[D. A. Dixon]

This article probably belongs in net.dcom but since the original
article appeared in this news group I am responding here.

I was one of the developers on a project here at Bell Laboratories -
Indian Hill that used both 4800 bps and 9600 bps synchronous modems
for teleprocessing data. The protocol we used was BX.25, the BTL
interpretation of X.25. For the 4800 bps data links we used Bell system
2048A modems and for the 9600 bps link we used 2096A's. We could have used
209A modems for the 9600 bps link but chose the 2096's since they are
newer and, in my opinion, better than the 209's. The 2048A and 2096A
contain software to allow you to easily set the options and to diagnose
the data link if trouble occurs. However, the diagnostic facilities
of these modems can only be used if you use the RS-449 protocol
on both ends of the data link. The 2000 serries modems come factory
installed with the RS-232-C protocol due to the large number of
RS-232-C devices currently in service.

According to specifications the 2096A requires an 829B Data Aux Set
and data conditioning type D1 on the leased line (it supposedly only
works over leased lines - more on this a little later). However,
when Illinois Bell installed the data link I used for the project
they did NOT use a Data Aux Set (they said it was up to the phone
company to decide if a DAS was needed on a line or not). The
2048A can be used on both leased lines and dial-up lines.
For dial-up arrangements you need a 48ER1, 48FR1, an 801 ACU,
and a single number dialer arranged in a dial-up/dial-back setup.
We found from experiments that a 2096A could be slid into such
an arrangement in place of the 2048A and still work reasonably well.

The 2048A can communicate with a 208A (providing both
use the RS-232-C protocol) but a 2096A is NOT line signal compatible
with a 209A; i.e., if you have a 2096 at one end of the link, you must
have a 2096 at the other end. Likewise for the 209.

All 9600 bps synchronous modems that I know of cost at least $2500.
The 2096A is no exception.

D A Dixon    ihuxa!dixon