[ih] Arpanet physical connectors

[Steve Crocker]

Vint,

What year was that connection established?

Steve

On Thu, Jul 23, 2020 at 10:04 AM Vint Cerf <vint at google.com> wrote:

> at Stanford my PDP-11/20 was connected by VDH to an IMP in another
> building on the campus.
>
> v
>
>
> On Thu, Jul 23, 2020 at 9:56 AM Steve Crocker via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
>> Much of this has been covered already in responses to your note, but we
>> can
>> add a little more.  The connectors were definitely NOT RS-232.  The BBN
>> team designed the connector.  I believe they wanted it to be as simple as
>> possible.  It was bit serial, operating at 100 kilobits per second.  The
>> lines connecting the IMPs operated at 50 kilobits per second, so 100 kb/s
>> was a reasonable fit.  Making it run much faster wouldn't have made a
>> noticeable difference in the overall performance.  The interface was
>> designed to operate up to 50 feet from the host.  A different interface
>> was
>> designed later to operate up to, I think, 1000 feet.  These were referred
>> to as the Local Host (LH) and Distant Host (DH)  interface.  A third
>> version was designed yet later to operate over unlimited distance.  It was
>> called the Very Distant Host (CDH) interface.
>>
>> I believe Severo Ornstein and Ben Barker were the key hardware people at
>> BBN.  Mike Wingfield at UCLA built the first host interface for our Sigma
>> 7.  All are copied on this message.  BBN Report 1822 has the details, as
>> reported in other messages.
>>
>> As noted, each site had to figure out how to connect the IMP into its
>> host.  This required a separate design and implementation at each of the
>> initial sites, and thus it was indeed important to have competent EE
>> people
>> involved.  After a while, ACC and DEC and perhaps others started to make
>> interfaces available for various hosts.
>>
>> Steve
>>
>>
>> On Thu, Jul 23, 2020 at 8:02 AM Stephane Bortzmeyer via Internet-history <
>> internet-history at elists.isoc.org> wrote:
>>
>> > https://twitter.com/nielstenoever/status/1286254151874293760
>> >
>> > Dear Internet History nerds, what did the connectors and cables of the
>> > ARPAnet look like?
>> >
>> > Were these serial cables? Seems likely because the RS-232 standard dates
>> > back to 1960.
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