[ih] principles of the internet

[John Day]

At 17:31 -0400 2010/06/01, Noel Chiappa wrote:
>     > From: John Day <jeanjour at comcast.net>
>
>     > Yes, this was the basic datagram innovation pioneered by CYCLADES,
>     > which is the fundamental shift in the thinking. I sometimes
>     > characterize the distinction as packet switching was "continental
>     > drift" but datagrams were "plate tectonics."
>
>Going to disagree with you there.
>
>Don't get me wrong, CYCLADES was a _HUGE_ step forward, and considering the
>gap from the ARPANET to the Internet, CYCLADES is much close to the latter
>than the former. So it was a critical trail-breaker. Still...
>
>The ARPANet really did pretty well implement the radical Baran/etc model of
>the world, the model of packets. That was the really fundamental change in the
>world, the strata-breaking event (to continue the geological metaphor).  Prior
>to that, circuits (with a whole range of key attributes, such as explicit
>setup/tear-down, fixed sharing of resources, stream service model, etc,
>etc). After that... And everything else since then has been adjustments to
>that major change in direction, IMO.

Sorry, but neither Baran nor the ARPANET were a datagram network. 
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. 
There is nothing about the IMP subnet that was "building reliable 
systems from unreliable parts." Also Baran's report and the ARPANET 
had much more in common with the virtual circuit approach to packet 
switching than the datagram approach.

Later the ARPANET added Type 3 packets to provide a datagram service, 
but it was not part of the original.  Also, the ARPANET was designed 
to be reliable.  The IMP subnet was not designed to lose packets. 
This is not a datagram network in the sense of CYCLADES or the 
Internet.

My geologic analogy was more to show that often when a paradigm shift 
occurs, it actually comes in stages with many contributors to get 
from the old model to the new.  All of the steps are necessary and 
probably all of them could not have been made by one person.

Actually your point about packet switching being a radical break is 
interesting.  (I must have said this before on this list)  In 
listening to people talk about it, a pattern emerges. If your 
formative years were in the world of traditional telecom, then yes, 
packet switching is a watershed change in your thinking.  But if you 
are just a little bit younger (and the shift is really only a couple 
of years) and your formative years were more with computing, then 
packet switching is "obvious."  (You want to send data between two 
computers?  Okay, the data is in buffers, pick up a buffer and send 
it.  Pretty obvious.)  But the idea, that packets could move 
independently, that the system could be stochastic.  That was 
mind-blowing.

>
>The ARPANet really did expose the datagram paradigm to the users (from its
>perspective, the hosts): for example, there was no 'connection open' or
>'connection close' _from the host to the IMP_ - the host just sent packets to
>whereever, and whenever, it wanted.


>
>Yes, it had to obey flow-control restrictions, or it could be blocked - but
>even if a host did obey flow-control, it could be blocked for reasons beyond
>its control/understanding.
>
>And, yes, the Host-Host protocols sort of 'made' the actual users use the
>network as VCs, but that was I think for other reasons (which I can only
>guess, but I would guess that keeping the circuit paradigm made getting into
>that whole new world easier).
>
>
>The big change going from the ARPANET (not Host-Host Protocol, see above) to
>the Internet (in terms of the _placement_ of function - the Internet of course
>added other capabilities, such as being able to use a diverse range of
>technologies, but that's different) was to make the hosts responsible for
>reliable transmission (checksums, sequence numbers, timeouts,
>retransmissions). Was that as big as going to packets to begin with? It was
>big, sure, but as big as going to packets?

Correct.  That (i.e. make the hosts responsible for reliable 
transmission (checksums, sequence numbers, timeouts, retransmissions) 
is what the CYCLADES TS protocol (its transport protocol) did in 
1972. It was not new with the Internet.  This was the whole point of 
a datagram based network.

Take care,
John