[ih] More topology

Steve Crocker steve at shinkuro.com
Sun Aug 29 09:55:26 PDT 2021 

Each IMP had four host ports.  ISI had more than four machines that needed
to be on the Arpanet, hence the second IMP.

Steve


On Sun, Aug 29, 2021 at 12:43 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:

> Actually July 1981 -- see
> http://mercury.lcs.mit.edu/~jnc/tech/jpg/ARPANet/G81Jul.jpg (thanks,
> Noel!)    The experience I recall was being in the ARPANET NOC for some
> reason and noticing the topology on the big map that covered one wall of
> the NOC.   There were 2 ARPANET nodes at that time labelled ISI, but I'm
> not sure where the PDP-10s were attached.   Still just historically
> curious how the decision was made to configure that topology....but
> we'll probably never know.  /Jack
>
>
> On 8/29/21 8:02 AM, Alex McKenzie via Internet-history wrote:
> >   A look at some ARPAnet maps available on the web shows that in 1982 it
> was four hops from ARPA to ISI, but by 1985 it was one hop.
> > Alex McKenzie
> >
> >      On Sunday, August 29, 2021, 10:04:05 AM EDT, Alex McKenzie via
> Internet-history <internet-history at elists.isoc.org> wrote:
> >
> >    This is the second email from Jack mentioning a point-to-point line
> between the ARPA TIP and the ISI site.  I don't believe that is an accurate
> statement of the ARPAnet topology.  In January 1975 there were 5 hops
> between the 2 on the shortest path. In October 1975 there were 6.  I don't
> believe it was ever one or two hops, but perhaps someone can find a network
> map that proves me wrong.
> > Alex McKenzie
> >
> >      On Saturday, August 28, 2021, 05:06:54 PM EDT, Jack Haverty via
> Internet-history <internet-history at elists.isoc.org> wrote:
> >
> >   Sounds right.   My experience was well after that early experimental
> > period.  The ARPANET was much bigger (1980ish) and the topology had
> > evolved over the years.  There was a direct 56K line (IIRC between
> > ARPA-TIP and ISI) at that time.  Lots of other circuits too, but in
> > normal conditions ARPA<->ISI traffic flowed directly over that long-haul
> > circuit.   /Jack
> >
> > On 8/28/21 1:55 PM, Vint Cerf wrote:
> >> Jack, the 4 node configuration had two paths between UCLA and SRI and
> >> a two hop path to University of Utah.
> >> We did a variety of tests to force alternate routing (by congesting
> >> the first path).
> >> I used traffic generators in the IMPs and in the UCLA Sigma-7 to get
> >> this effect. Of course, we also crashed the Arpanet with these early
> >> experiments.
> >>
> >> v
> >>
> >>
> >> On Sat, Aug 28, 2021 at 4:15 PM Jack Haverty <jack at 3kitty.org
> >> <mailto:jack at 3kitty.org>> wrote:
> >>
> >>      Thanks, Steve.  I hadn't heard the details of why ISI was
> >>      selected.   I can believe that economics was probably a factor but
> >>      the people and organizational issues could have been the dominant
> >>      factors.
> >>
> >>      IMHO, the "internet community" seems to often ignore non-technical
> >>      influences on historical events, preferring to view everything in
> >>      terms of RFCs, protocols, and such.  I think the other influences
> >>      are an important part of the story - hence my "economic lens".
> >>      You just described a view through a manager's lens.
> >>
> >>      /Jack
> >>
> >>      PS - I always thought that the "ARPANET demo" aspect of that
> >>      ARPANET timeframe was suspect, especially after I noticed that the
> >>      ARPANET had been configured with a leased circuit directly between
> >>      the nearby IMPs to ISI and ARPA.   So as a demo of "packet
> >>      switching", there wasn't much actual switching involved.   The 2
> >>      IMPs were more like multiplexors.
> >>
> >>      I never heard whether that configuration was mandated by ARPA, or
> >>      BBN decided to put a line in as a way to keep the customer happy,
> >>      or if it just happened naturally as a result of the ongoing
> >>      measurement of traffic flows and reconfiguration of the topology
> >>      to adapt as needed.  Or something else.   The interactivity of the
> >>      service between a terminal at ARPA and a PDP-10 at ISI was
> >>      noticeably better than other users (e.g., me) experienced.
> >>
> >>      On 8/28/21 11:51 AM, Steve Crocker wrote:
> >>>      Jack,
> >>>
> >>>      You wrote:
> >>>
> >>>          I recall many visits to ARPA on Wilson Blvd in Arlington, VA.
> >>>          There were
> >>>          terminals all over the building, pretty much all connected
> >>>          through the
> >>>          ARPANET to a PDP-10 3000 miles away at USC in Marine Del Rey,
> >>>          CA.  The
> >>>          technology of Packet Switching made it possible to keep a
> >>>          PDP-10 busy
> >>>          servicing all those Users and minimize the costs of
> everything,
> >>>          including those expensive communications circuits.  This was
> >>>          circa
> >>>          1980. Users could efficiently share expensive communications,
> and
> >>>          expensive and distant computers -- although I always thought
> >>>          ARPA's
> >>>          choice to use a computer 3000 miles away was probably more to
> >>>          demonstrate the viability of the ARPANET than because it was
> >>>          cheaper
> >>>          than using a computer somewhere near DC.
> >>>
> >>>
> >>>      The choice of USC-ISI in Marina del Rey was due to other
> >>>      factors.  In 1972, with ARPA/IPTO (Larry Roberts) strong support,
> >>>      Keith Uncapher moved his research group out of RAND.  Uncapher
> >>>      explored a couple of possibilities and found a comfortable
> >>>      institutional home with the University of Southern California
> >>>      (USC) with the proviso the institute would be off campus.
> >>>      Uncapher was solidly supportive of both ARPA/IPTO and of the
> >>>      Arpanet project.  As the Arpanet grew, Roberts needed a place to
> >>>      have multiple PDP-10s providing service on the Arpanet.  Not just
> >>>      for the staff at ARPA but for many others as well.  Uncapher was
> >>>      cooperative and the rest followed easily.
> >>>
> >>>      The fact that it demonstrated the viability of packet-switching
> >>>      over that distance was perhaps a bonus, but the same would have
> >>>      been true almost anywhere in the continental U.S. at that time.
> >>>      The more important factor was the quality of the relationship.
> >>>      One could imagine setting up a small farm of machines at various
> >>>      other universities, non-profits, or selected for profit companies
> >>>      or even some military bases.  For each of these, cost,
> >>>      contracting rules, the ambitions of the principal investigator,
> >>>      and staff skill sets would have been the dominant concerns.
> >>>
> >>>      Steve
> >>>
> >>
> >>
> >> --
> >> Please send any postal/overnight deliveries to:
> >> Vint Cerf
> >> 1435 Woodhurst Blvd
> >> McLean, VA 22102
> >> 703-448-0965
> >>
> >> until further notice
> >>
> >>
> >>
>
>
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