[ih] principles of the internet

[Noel Chiappa]

    > 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).

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).


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.

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'.

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.


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?

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.

	Noel