[ih] ARPA initial IMP-IMP line speed

Mike Brescia m.brescia at comcast.net
Tue Feb 24 13:31:43 PST 2004


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 

  -- 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

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