[ih] Arpanet line speed

[Jack Haverty]

For the historians - what those expensive "high-speed" lines actually
looked like...

I was one of the setup crew at the ICCC '72 demonstration of the ARPANET
in the ballroom of the Washington Hilton.  We had laid a false floor to
cover all the wiring between a gaggle of terminals and the TIP, put
various terminals, printers, and of course the TIP right in the middle
of the room, and were awaiting the Telco guy to come with The Line.

I expected some kind of impressive cable with esoteric connector, as
would befit the rare not-so-ordinary phone line.

When the phone guy arrived, he dragged over a ratty looking pile of thin
cable from the wall of the ballroom, and stretched it out to reach the
IMP.  It looked like what you might use to hook up your doorbell.  Or an
extension phone in your house.  Just a couple of small wires to hook up,
IIRC.  Probably the ones they had used for the last umpteen meetings in
that room where they wanted a phone.

Since it wasn't very impressive, we hid it under the false floor, duct
tape, etc. and hoped nobody would trip over it.

I remember being amazed that you could possibly get 50+ kilobits/second
over such wiring.  Of course I'm even more amazed at the gigabit/second
flowing over the tiny Ethernet wires attached to my desktop today.

/Jack

On 01/18/2017 10:56 AM, Andrew G. Malis wrote:
> Noel,
> 
> They were digital DS0s. I’m sure that they were less expensive than
> analog (although I have no particular documentation of that), and most
> probably more reliable as well. As I recall, with the digital circuits,
> the most common cause of line outage was microwave fade.
> 
> Cheers,
> Andy
> 
> 
> On Wed, Jan 18, 2017 at 1:32 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu
> <mailto:jnc at mercury.lcs.mit.edu>> wrote:
> 
>         > From: "Andrew G. Malis"
> 
>         > By the time I came on board in '79, almost all of the links
>     were 56
>         > Kbps ... The 50 Kbps links had been replaced by that point.
> 
>     Hmmm. I'm trying to remember when the giant rack that contained the 303
>     modems at MIT went away. (I should remember this, as I wound up
>     caring for
>     the MIT IMPs, but I just don't recall.) Do you know any details of
>     how the
>     56Kbps links worked? I.e. was there a analog modem involved, or was it
>     somehow provided by an underlying digital (TDMA of some sort) link,
>     and what
>     kind of line was it?
> 
>     Do you know why the change was made? I'm going to guess that
>     possibly it was
>     cost, that whatever was used for the 56kbps was cheaper than the
>     leased lines
>     used with the 303s?
> 
>             Noel
> 
> 
> 
> 
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