[ih] More topology

[Vint Cerf]

two tcp connections could multiplex on a given IMP-IMP link - one RFNM per
IP packet regardless of the TCP layer "connection"
v


On Sun, Aug 29, 2021 at 10:30 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:

> Thanks Barbara -- yes, the port Expander was one of the things I called
> "homegrown LANs".  I never did learn how the PE handled RFNMs, in
> particular how it interacted with its associated NCP host that it was
> "stealing" RFNMs from.
> /jack
>
> On 8/29/21 2:38 PM, Barbara Denny wrote:
> > There was also SRI's port expander which increased the number of host
> > ports available on an IMP.
> >
> > You can find the SRI technical report (1080-140-1) on the web. The
> > title is "The Arpanet Imp Port Expander".
> >
> > barbara
> >
> > On Sunday, August 29, 2021, 12:54:39 PM PDT, Jack Haverty via
> > Internet-history <internet-history at elists.isoc.org> wrote:
> >
> >
> > Thanks Steve.   I guess I was focussed only on the longhaul hops. The
> > maps didn't show where host computers were attached. At the time
> > (1981) the ARPANET consisted of several clusters of nodes (DC, Boston,
> > LA, SF), almost like an early form of Metropolitan Area Network (MAN),
> > plus single nodes scattered around the US and a satellite circuit to
> > Europe.  The "MAN" parts of the ARPANET were often richly connected, and
> > the circuits might have even been in the same room or building or
> > campus.   So the long-haul circuits were in some sense more important in
> > their scarcity and higher risk of problems from events such as marauding
> > backhoes (we called such network outages "backhoe fade").
> >
> > While I still remember...here's a little Internet History.
> >
> > The Internet, at the time in late 70s and early 80s, was in what I used
> > to call the "Fuzzy Peach" stage of its development.  In addition to
> > computers directly attached to an IMP, there were various kinds of
> > "local area networks", including things such as Packet Radio networks
> > and a few homegrown LANs, which provided connectivity in a small
> > geographical area.  Each of those was attached to an ARPANET IMP
> > somewhere close by, and the ARPANET provided all of the long-haul
> > communications.   The exception to that was the SATNET, which provided
> > connectivity across the Atlantic, with a US node (in West Virginia
> > IIRC), and a very active node in the UK.   So the ARPANET was the
> > "peach" and all of the local networks and computers in the US were the
> > "fuzz", with SATNET attaching extending the Internet to Europe.
> >
> > That topology had some implications on the early Internet behavior.
> >
> > At the time, I was responsible for BBN's contract with ARPA in which one
> > of the tasks was "make the core Internet reliable 24x7".   That
> > motivated quite frequent interactions with the ARPANET NOC, especially
> > since it was literally right down the hall.
> >
> > TCP/IP was in use at the time, but most of the long-haul traffic flows
> > were through the ARPANET.  With directly-connected computers at each
> > end, such as the ARPA-TIP and a PDP-10 at ISI, TCP became the protocol
> > in use as the ARPANET TIPs became TACs.
> >
> > However...   There's always a "however"...  The ARPANET itself already
> > implemented a lot of the functionality that TCP provided. ARPANET
> > already provided reliable end-end byte streams, as well as flow control;
> > the IMPs would allow only 8 "messages" in transit between two endpoints,
> > and would physically block the computer from sending more than that.
> > So IP datagrams never got lost, or reordered, or duplicated, and never
> > had to be discarded or retransmitted.   TCP/IP could do such things too,
> > but in the "fuzzy peach" situation, it didn't have to do so.
> >
> > The prominent exception to the "fuzzy peach" was transatlantic traffic,
> > which had to cross both the ARPANET and SATNET.   The gateway
> > interconnecting those two had to discard IP datagrams when they came in
> > faster than they could go out.   TCP would have to notice, retransmit,
> > and reorder things at the destination.
> >
> > Peter Kirstein's crew at UCL were quite active in experimenting with the
> > early Internet, and their TCP/IP traffic had to actually do all of the
> > functions that the Fuzzy Peach so successfully hid from those directly
> > attached to it.   I think the experiences in that path motivated a lot
> > of the early thinking about algorithms for TCP behavior, as well as
> > gateway actions.
> >
> > Europe is 5+ hours ahead of Boston, so I learned to expect emails and/or
> > phone messages waiting for me every morning advising that "The Internet
> > Is Broken!", either from Europe directly or through ARPA.  One of the
> > first troubleshooting steps, after making sure the gateway was running,
> > was to see what was going on in the Fuzzy Peach which was so important
> > to the operation of the Internet.   Bob Hinden, Alan Sheltzer, and Mike
> > Brescia might remember more since they were usually on the front lines.
> >
> > Much of the experimentation at the time involved interactions between
> > the UK crowd and some machine at ISI.   If the ARPANET was acting up,
> > the bandwidth and latency of those TCP/IP traffic flows could gyrate
> > wildly, and TCP/IP implementations didn't always respond well to such
> > things, especially since they didn't typically occur when you were just
> > using the Fuzzy Peach.
> >
> > Result - "The Internet Is Broken".   That long-haul ARPA-ISI circuit was
> > an important part of the path from Europe to California.   If it was
> > "down", the path became 3 or more additional hops (IMP hops, not IP),
> > and became further loaded by additional traffic routing around the
> > break.   TCPs would timeout, retransmit, and make the problem worse
> > while their algorithms tried to adapt.
> >
> > So that's probably what I was doing in the NOC when I noticed the
> > importance of that ARPA<->USC ARPANET circuit.
> >
> > /Jack Haverty
> >
> >
> > On 8/29/21 10:09 AM, Stephen Casner wrote:
> > > Jack, that map shows one hop from ARPA to USC, but the PDP10s were at
> > > ISI which is 10 miles and 2 or 3 IMPs from USC.
> > >
> > >         -- Steve
> > >
> > > On Sun, 29 Aug 2021, Jack Haverty via Internet-history wrote:
> > >
> > >> Actually July 1981 -- see
> > >> http://mercury.lcs.mit.edu/~jnc/tech/jpg/ARPANet/G81Jul.jpg
> > <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
> > <mailto: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
> > <mailto: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>
> > >>>> <mailto: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 <(703)%20448-0965>
> > >>>>
> > >>>> until further notice
> >
> >
> > --
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> > <https://elists.isoc.org/mailman/listinfo/internet-history>
>
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>


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