[ih] principles of the internet

[John Day]

At 20:44 -0400 2010/06/01, Noel Chiappa wrote:
>     > From: John Day <jeanjour at comcast.net>
>
>     > Sorry, but neither Baran nor the ARPANET were a datagram network.
>
>Well, it all depends on how you define 'datagram network', doesn't it?! :-)
>
>     > There are two aspects to being a datagram network: 1) the independent
>     > routing of the packets, and 2) the network does not try to recover all
>     > failures, but leaves most of that to the hosts.
>
>Those are both important, but I would say that 'no call setup' is equally
>important. By your definition, an ATM network might be a 'datagram network'
>(well, maybe not, I guess it doesn't have true independent routing of packets
>through intermediate nodes).

Strictly speaking there is always some form of "call setup" even if 
it is by "ad-hoc" means, i.e. some code it in or a management system 
configures it.  Something must ensure there is something that expects 
the packet on the other end.  There is no magic.

The idea that connectionless has no connection set up turns out to be 
a problem of drawing boundaries so you can ignore it.  It is there. 
You have to look to other characteristics, such as independence of 
routing, assuming higher layer reliability, etc.

>
>And if you go look at the detail in 1822, there is an error code in there for
>'packet not received at the other end', with the implication that it's up to
>the host to retry (although as we previously discussed some months back, no
>host seems to have actually done so, since in practise the network was too
>reliable to bother).

Correct.  Grossman once told me he remembered either Heart or Walden 
pounding a table in a meeting saying words to the effect "my network 
won't lose anything."  ;-)

>
>Was the ARPANET a driven-snow pure datagram network? No, it didn't fully have
>the 'unreliable network' thing. But it still was a huge step towards the pure
>datagram network of today - it had packets, it had the pooled resource
>allocation, it had no call setup, it had independent routing of packets, etc,
>etc. All it was missing was the 'hosts do reliability' thing.

Yes, this is my point, the paradigm shift was not a step function. 
Baran starts it, the ARPANET takes a few more steps, but conceptually 
it is CYCLADES that first puts all the elements together.  You are 
aware that BBN guys were making monthly trips to INRIA while CYCLADES 
was being built to advise them and help them avoid some of the 
mistakes they made?  (Walden told me that).

I am beginning to suspect that you misunderstood my geologic analogy. 
It was not a question of right and wrong.  Continental drift was not 
wrong, it was right.  Continental drift got people to look at the 
problem which lead to further insights. Plate tectonics refined the 
concept   One was not possible without the other.  The same here.

>
>You may claim that this was the hard step intellectually, and that what came
>before (all the stuff the ARPANET did) was sort of 'engineering necessity'.

No, not a hard step. That is the whole point it wasn't.

>
>But I seem to recall at least once Vint saying that the 'hosts do
>reliability' thing was just unavoidable for them once they tried to hook
>SATNET (or a PRNET) to the ARPANET, that the ARPANET model just didn't work
>once you tried to hook a number of networks together; that's exactly why
>TCP/IP wound up looking the way it did. So there was 'engineering necessity'
>there too.

Yes, this is much later.  As we moved out to encompass more things, 
the complexities began to arise. This is also lead to the realization 
later that the structure of the Data Link and Network Layers were not 
as simple as we first thought, nor was it always the same.

>
>
>I think what may be going on here is that a lot of ideas that are 'obvious'
>in retrospect aren't actually so obvious beforehand - and unless you lived
>through the phase-change, you don't really appreciate, at a gut level, just
>how 'non-obvious' they really were beforehand.
>
>(Like the WWW.... but I digress! :-)
>
>You and I never lived in a world in which the idea of a packet didn't exist,
>so I'm not sure we can really understand how 'non-obvious' that idea was,
>before Baran et al. You, I gather, did live through the idea of 'hosts do
>reliability', so you probably do have an idea of how 'non-obvious' it was.
>But perhaps that you lived through one, and not the other, is affecting your
>analysis of how important they were, relative to each other?

Well, actually I did live in a world with out packets (for a little 
bit) but as a computer person not as a telecom person.  This is what 
I mean.  As with most things in history, when talking to a 
participant, their view of what happened is conditioned by their 
history.  They are interpreting events and facts in terms of their 
background.

This is what I mean that for people of one age group whose background 
was telecom they had always thought communication meant one thing. 
For another group with an entirely different experience thinking in 
terms of distributed systems, it was something completely different.

>
>Yes, CYCLADES was very important in both i) floating the idea of 'hosts do
>reliability', and ii) showing that a working network could actually be built
>out of it... but much as I want to honour it (and see that it's remembered),
>I still don't think it's as big a step as the step to the ARPANET.

You needed both.  Baran's ideas weren't real until there was the 
ARPANET.  (The thing that saved our bacon was that it was the DoD who 
did and was willing to spend like crazy on it.  Because otherwise it 
wouldn't have looked as good as it did.  Imagine if the Net had 9.6K 
lines instead of 56K. It would have been seen entirely differently. 
But it was seeing the ARPANET that got Pouzin to thinking what the 
next step was.  Pouzin's ideas weren't real until CYCLADES was 
operational.  CYCLADES wouldn't have worked as well as it did without 
the input from BBN.

You are looking at this too much as an either-or.  It is the 
messiness that I am trying to draw attention to. And that it wasn't 
entirely a US effort.  If you read this list one gets the idea that 
the only things that ever happened were either at ISI or MIT and few 
guys at Stanford.  Also that for most of the world (of researchers) 
the Internet wasn't even on their screens.  Perhaps it should have 
been.  We might not be in the mess we currently find ourselves.

This was a very creative period.  There was huge exchange of ideas 
and some very insightful people.

Take care,
John

>	Noel