[net.periphs] 9600 full-duplex, by trickery?

henry@utzoo.UUCP (Henry Spencer) (10/16/84)

A recent issue of Electronics Week has a very interesting ad on the back
cover.  It's from Universal Data Systems (Motorola's modem subsidiary),
and what it plugs is a UDS 9600 A/B -- a fairly ordinary 9600-baud half-
duplex modem -- plus an "EC100" box which does error correction *and*
makes the half-duplex modem look full-duplex!

Does anybody know how well this thing works?  I assume that the EC100,
error-correction functions aside, is basically just some buffering and
an intelligent line-turnaround algorithm.  If one assumes that total
average traffic, both directions together, is somewhat under 960 cps,
then making a half-duplex channel look full-duplex is indeed feasible.
They're pushing it for terminals, where the assumption is plausible,
but it might work well enough for things like uucp.

They say "for details, phone (800)633-2252 x356".  Unfortunately, when
I try this I get an error message from the phone company.  (Probably
because there's this international border in between...)

Anyone ever heard of this widget, or worked with one?
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry

rbt@sftig.UUCP (R.Thomas) (10/17/84)

>                                        a fairly ordinary 9600-baud half-
> duplex modem -- plus an "EC100" box which does error correction *and*
> makes the half-duplex modem look full-duplex!
> 
>                                            If one assumes that total
> average traffic, both directions together, is somewhat under 960 cps,
> then making a half-duplex channel look full-duplex is indeed feasible.
> They're pushing it for terminals, where the assumption is plausible,
> but it might work well enough for things like uucp.
> 
> 				Henry Spencer @ U of Toronto Zoology
> 				{allegra,ihnp4,linus,decvax}!utzoo!henry

It might work *very* well for uucp.  Uucp is essentially half-duplex.
When one side is sending, the other side is (nearly) idle (except for
things like x-on/x-off).  The only problem is to make sure that both
sides have one of them.  (The old chicken and egg problem!)

henry@utzoo.UUCP (Henry Spencer) (11/08/84)

A friend of mine helpfully called UDS and gave them my name for an
information packet on their modems.  It came today.  The news isn't
really terribly good.  The "9600 A/B" is indeed a 9600-baud dialup
half-duplex modem, and the "EC100" will indeed make it look full-
duplex provided the aggregate bidirectional traffic stays below the
actual half-duplex line throughput.  The modem matches CCITT V.24,
with fallback speeds of 7200 and 4800.  The EC100 has 4KB of buffer
and does CRC and an acknowledgement protocol.

Now the bad parts.  First, the modem does not speak 212 or 103, so
there is no backward compatibility on a phone line fitted with one
of these.  Second, the modem does not autodial, so you'll need a
separate autodialer box (UDS will happily sell you one).  And third,
after you add up the price tags, equipping one phone line with modem,
EC100, and dialer comes out at US$3100.  Oh well.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry