[ih] ARPA initial IMP-IMP line speed

[Toru Nohzawa ,]

Thanks Mike,

According to the 1987 BBN report you mentioned, "Bell Data Station 303-type"
supports 230.4K, 50K, 19.2K with internal clock  selection. Therefore If
IMP did use Bell Data Station 303-type,  50K was reasonable.
(By the way, what is "Data Station 303-type" ?  We know Bell 103, 212 as a
modem. So "303" could be the analog modem we are talking about, I hope. )

Yes, I know  Waldrop's "The Dream Machine" mentioning 50Kbps. But his
description of  "The idea was that you bought a very expensive modem that
tied twelve lines together"  causes me some confusion. The straight forward
interpretation of the sentence is "AT&T provides 9.6Kx12lines". But the word
"idea" sound something like "analogy". Then, the sentence could be
interpretable like  "actually 50K but analogous to 9.6x12". In addition,
9.6x12=115.2, 9.6x6=57.6. It doesn't agree with 50K.
Therefore, I think this portion of the book gives some confusion to the
careful non-modem-background readers.

I recommend we have better to describe the Iine speed of IMP-IMP at 1969
more clearly such as  " 50Kbps through the specially ordered analog
wideband.least line" , to avoid confusion with current 56K voice band modem.

Toru


----Original Message-----
From: Mike Brescia [mailto:m.brescia at comcast.net]
Sent: Wednesday, February 25, 2004 6:32 AM
To: Toru Nohzawa ,
Cc: internet-history at postel.org
Subject: RE: [ih] ARPA initial IMP-IMP line speed

Hi,

The decision to use 50kb instead of 9.6kb as mentioned in "The Dream
Machine"* was made by Larry Roberts as the ARPA program manager for
the network project.
"what the phone companies called a 50-kilobit line."  [The Dream
Machine, J.C.R.Licklider and the Revolution That Made Computing
Personal, M.Mitchell Waldrop, Viking, New York, 2001, ISBN
0-670-89976-3 -- page 276]

A reference in the 1987 report describing interfaces on a compatable
IMP http://www.totallynerd.com/library/files/c30e_int.txt mentions
the modem equipment -- Bell  System  Technical  Reference;  "Wideband
Data Stations
303-Type," August 1966.

>Do you know somebody who handled the communication portion of the IMP ?

All who I have heard from agree that 50kb was the speed.  There were
experiments with a 230.4kb service but the concerns were with the
economics of renting the lines and the overall computing capacity of
the IMPs.

Most of us who have responded to your notes are computer people, not
modem hardware or telecomms people.  We have some recollections of
descriptions of what went on in the telco equipment, bandwidth and
the hierarchies of voice circuit aggregation.  You need to find
people who were closer to AT&T, Bell Labs or Western Electric,
perhaps Lucent now, to get more detail about wiring, encoding or
equipment.

Regards,
  -- Mike (BBN &seq.1978-2002)

Disclaimer: I have no connection with Mr. Waldrop or the "Dream
Machine" book other than that I have a copy. - m