[ih] More topology
Barbara Denny
b_a_denny at yahoo.com
Sun Aug 29 14:38:13 PDT 2021
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 (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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