[ih] Installed base momentum (was Re: Design choices in SMTP)

[Jack Haverty]

It seems that I didn't receive some messages over the weekend....sorry 
if anyone has already noted what I say below.

Re the ARPANET and Congestion Control:   This was definitely a hot 
topic, in particular after DCA took over operations and the network grew 
in size.   There were DCA-managed contracts to rework the internal 
mechanisms of the ARPANET to handle the much larger and diverse networks 
of IMPs that evolved into the multiple IMP-based networks called the 
DDN.   Congestion control was just one issue of several that interacted, 
e.g., routing, flow control, retransmission, buffer management, etc.  
The IMP design, although a "packet network", in effect had a "serial 
byte stream" mechanism internally to make sure all data got from source 
host to destination.  The ARPANET had the equivalent of parts of a TCP 
built inside the IMPs to guarantee the delivery of a data stream.

I'm not sure how much historical detail you'll find in traditionally 
published papers and journals.   Outside of academia that wasn't a 
priority.  But there were extensive and detailed reports prepared as 
part of the ARPANET "operations" contracts and delivered to DCA. Here's 
one 3-volume, multi-year example that discusses a lot of the work in the 
early 80s on "congestion control" and new internal IMP mechanisms in 
general:

https://apps.dtic.mil/sti/citations/ADA053450
https://apps.dtic.mil/sti/citations/ADA086338
https://apps.dtic.mil/sti/citations/ADA121350

There's hundreds of pages of detail in those reports and there are 
others available through DTiC.   I was listed as author on some of 
these, because at the time that contract was one of "my" contracts -- 
which meant that I had to make sure that the report got written and 
delivered so we would get paid.   I didn't personally work on the 
ARPANET technical research, but I did absorb some understanding of the 
issues and details.  The "IMP Group" was literally just down the hall.

At the time (early 1980s), I was involved in the early Internet work, 
when TCP/IP V4 was being created and the various flow and congestion 
control mechanisms were being defined.  From the ARPANET experience, it 
was clear to me that the IMP gurus "down the hall" at BBN viewed 
congestion control as a major issue, and that sometimes surfaced as 
statements such as "TCP will never work".  TCP didn't address any of the 
issues of congestion, except by the rudimentary and unproven mechanism 
of "Source Quench".

The expectation was that the Internet would work if congestion was 
avoided rather than controlled, which could be attempted by keeping 
network capacity above traffic demands, at least long enough that TCP's 
retransmission and backoff mechanisms in the hosts would throttle down 
as expected to match what the network substrate was capable of carrying 
at the time.   Of course those mechanisms were now distributed among the 
several hosts and network switches (e.g., IMPs, Packet Radios, computer 
OS, gateways) involved, designed, built, and managed by different 
organizaions, which made it challenging to predict how it would all behave.

Even today, as an end user, I can't tell if "congestion control" is 
implemented and working well, or if congestion is just mostly being 
avoided by deployment of lots of fiber and lots of buffer memory in all 
the switching locations where congestion might be expected. That of 
course results in the phenomenon of "buffer bloat".   That's another 
question for the Historians.  Has "Congestion Control" in the Internet 
been solved?  Or avoided?

Jack Haverty



On 2/13/23 08:19, Craig Partridge via Internet-history wrote:
> On Sat, Feb 11, 2023 at 7:48 AM Noel Chiappa via Internet-history <
> internet-history at elists.isoc.org> wrote:
>
>>
>>      > From: Craig Partridge
>>
>>      > We figured out congestion collapse well enough for the time
>>
>> It should be remembered that the ARPANET people (hi!) had perhaps solved
>> this
>> problem a long time before. I'm trying to remember how explicitly they saw
>> this as a separate problem from the issue of running out of buffer space
>> for
>> message re-assembly at the destination IMP, but I seem to recall that RFNMs
>> were seen as a needed throttle to prevent the network as a whole from being
>> overrun (i.e. what we now think of as 'congestion', although IIRC that term
>> wasn't used then), as well as flow control to the source host (as we would
>> now call it).
>>
>> I don't recall exactly where I saw that, but I'd try the BBN proposal to
>> DARPA's RFP, and the first JFIPS paper ("The interface message processor
>> for
>> the ARPA computer network").
>>
> I don't recall the details either, though I remember stories of Bob Kahn
> going to LA to beat up on the first few ARPANET nodes
> because he anticipated various issues, I think including congestion.  And
> he found them and fixes were made.
>
> But remember ARPANET was homogeneous -- same speed for each link and a
> single control mechanism.  I think John Nagle was
> the first to point out ("On packet switches with infinite storage") that
> connecting very different networks had its own challenges.
> And to my point, not something that a person working with X.25 would have
> understood terribly well (yes X.75 gateways existed but
> they typically throttled the window size to 2 packets, which hid a lot of
> issues).
>
> Craig