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* [TUHS] TUHS Digest, Vol 14, Issue 63
@ 2017-01-17 15:32 Noel Chiappa
  2017-01-18 14:29 ` Paul Ruizendaal
  0 siblings, 1 reply; 18+ messages in thread
From: Noel Chiappa @ 2017-01-17 15:32 UTC (permalink / raw)


    > From: Joerg Schilling

    > Was T1 a "digital" line interface, or was this rather a 24x3.1 kHz
    > channel?

Google is your friend:

  https://en.wikipedia.org/wiki/T-carrier
  https://en.wikipedia.org/wiki/Digital_Signal_1


    > How was the 64 ??? Kbit/s interface to the first IMPs implemented?
    > Wasn't it AT&T that provided the lines for the first IMPs?

Yes and no. Some details are given in "The interface message processor for the
ARPA computer network" (Heart, Kahn, Ornstein, Crowther and Walden), but not
much.  More detail of the business arrangement is contained in "A History of
the ARPANET: The First Decade" (BBN Report No. 4799).

Details of the interface, and the IMP side, are given in the BBN proposal,
"Interface Message Processor for the ARPA Computer Network" (BBN Proposal No.
IMP P69-IST-5): in each direction there is a digital data line, and a clock
line. It's synchronous (i.e. a constant stream of SYN characters is sent
across the interface when no 'frame' is being sent).

The 50KB modems were, IIRC, provided by the Bell system; the diagram in the
paper above seems to indicate that they were not considered part of the IMP
system. The modems at MIT were contained in a large rack, the same size as
the IMP, which stood next to it.

I wasn't able to find anything about anything past the IMP/modem interface.
Perhaps some AT+T publications of that period might detail how the modem,
etc, worked.

	Noel


^ permalink raw reply	[flat|nested] 18+ messages in thread
* [TUHS] TUHS Digest, Vol 14, Issue 63
@ 2017-01-16 19:46 Noel Chiappa
  2017-01-17  0:30 ` Brad Spencer
  0 siblings, 1 reply; 18+ messages in thread
From: Noel Chiappa @ 2017-01-16 19:46 UTC (permalink / raw)


    > From: Larry McVoy

    > It is pretty stunning that the company that had the largest network in
    > the world (the phone system of course) didn't get packet switching at
    > all.

Actually, it's quite logical - and in fact, the lack of 'getting it' about
packets follows directly from the former (their large existing circuit switch
network).

This dates back to Baran (see his oral history:

  https://conservancy.umn.edu/handle/11299/107101

pg. 19 and on), but it was still detectable almost two decades later.

For a variety of all-too-human reasons (of the flavour of 'we're the
networking experts, what do you know'; 'we know all about circuit networks,
this packet stuff is too different'; 'we don't want to obsolete our giant
investment', etc, etc), along with genuine concerns about some real issues of
packet switching (e.g. the congestion stuff, and how well the system handled
load and overload), packet switching just was a bridge too far from what they
already had.

Think IBM and timesharing versus batch and mainframe versus small computers.

	Noel


^ permalink raw reply	[flat|nested] 18+ messages in thread
[parent not found: <mailman.1.1484532001.2693.tuhs@minnie.tuhs.org>]

end of thread, other threads:[~2017-01-18 14:29 UTC | newest]

Thread overview: 18+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-01-17 15:32 [TUHS] TUHS Digest, Vol 14, Issue 63 Noel Chiappa
2017-01-18 14:29 ` Paul Ruizendaal
  -- strict thread matches above, loose matches on Subject: below --
2017-01-16 19:46 Noel Chiappa
2017-01-17  0:30 ` Brad Spencer
     [not found] <mailman.1.1484532001.2693.tuhs@minnie.tuhs.org>
2017-01-16 16:00 ` Doug McIlroy
2017-01-16 16:22   ` Marc Rochkind
2017-01-16 16:44   ` Larry McVoy
2017-01-16 16:52     ` Marc Rochkind
2017-01-16 19:17     ` Steve Johnson
2017-01-16 19:21       ` Larry McVoy
2017-01-16 19:57         ` Ken Thompson
2017-01-16 23:41     ` Tim Bradshaw
2017-01-16 23:45       ` Brantley Coile
2017-01-17  4:07       ` Jason Stevens
2017-01-17  5:22         ` William Corcoran
2017-01-17 11:43     ` Jason Stevens
2017-01-17 14:27     ` Joerg Schilling
2017-01-17 14:21   ` Joerg Schilling

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