Communications of the ACM

This year is the 50th anniversary of the activation of the Arpanet project. The first packet switches (called Interface Message Processors or IMPs) were installed at UCLA,

SRI International [then Stanford Research Institute], UC Santa Barbara, and University of Utah. Host computers at UCLA and SRI made their first connection through the Arpanet on October 29, 1969.

Tom Standage’s book, The Victo-
rian Internet,a highlights the drama
of the arrival of the telegraph in the
mid-19th century. In its earliest incar-
nation, telegraph operators coded text
messages in Morse Codeb and sent
them to the next operator whose re-
ceiver was connected on a dedicated,
point-to-point wire. The transcribed
message was then re-sent by the re-
ceiving operator to the next one, pro-
ceeding hop-by-hop until it reached
the final operator who transcribed
the message and delivered it to the re-
cipient, typically by courier. This was
called a “store-and-forward” message-
switching system because at each hop,
messages were temporarily stored at
the intermediate telegraph operator’s
office until they could be re-sent to the
next operator.c
When teletype machines were in-
vented, they punched holes in paper
tape coded with 5 bits to represent up
to 32 characters or symbols. Eventu-
ally an 8-bit coding scheme was used
to expand the available character set
to include uppercase and lowercase
a T. Standage. The Victorian Internet. Walker &
Company, 1998; ISBN-13: 978-162040592, ISBN-

10: 162040592X, ISBN 0-8027-1342-4 (hardcov-
er), ISBN 978-0-8027-1604-0 (paperback).
b https://en.wikipedia.org/wiki/Morse_code
c For more information, see my June 2019 Cerf’s
Up column.
as well as other special characters. An
operator would enter a message on
the teletype and a paper tape would
be punched. The operator would tear
off the paper tape and hang it on a
peg next to the teletype that would be
used to send the message to the next
hop. This was called a “torn tape” sys-
tem since the punched paper tapes
would be torn from the originating
teletype and fed into a teletype that
would automatically read the tape
and send the signals to the next tele-
type. The receiving teletype, which
was connected by a dedicated circuit,
would then punch out a copy of the
message on a tape which would again
be torn from the machine …
Interestingly, the telephone emerged
from research attempting to allow
one wire to carry more than one tele-
graph message at the same time.
Telephone circuits were built manu-
ally with patch panels to connect the
caller to the called party. Eventually
automatic switching was possible
and circuits were built automatically
from source to destination. This al-
lowed teletypes to be directly con-
nected end-to-end without requir-
ing intermediate queueing. No more
store-and-forward was necessary as
the two end-points were directly con-
nected by a circuit.

Returning to the Arpanet, the chal-
lenge there was to find an alternative
to connecting the machines by way
of dial-up circuits. Such a process
would have been painfully slow since
each connection would take seconds
to complete while the computers,
The subsequent Internet made
use of circuits running at a minimum
of 1. 5 megabits/second in the early
1980s and today at 100–400 gigabits/
second. The transmission delays are
negligible, per hop, and are domi-
nated by speed of light and/or queue-
ing delays in the event of congestion.
So we have come full circle back to
the store-and-forward days of the
telegraph, but at sub-nanoseconds
of transmission delay per bit. We’ve
gone back to the future!