below.

On Wed, Nov 26, 2014 at 1:49 PM, Noel Chiappa <jnc@mercury.lcs.mit.edu> wrote:

> From: Clem Cole

A few comments on aspects I know something of:

> BTW: the Arpanet was not much better at the time

The people at BBN might disagree with you... :-)

Fair enough...

But seriously, throughout its life, the ARPANET had 'load-dependent routing',
i.e. paths were adjusted not just in response to links going up or down, but
depending on load (so that traffic would avoid loaded links).

The first attempt at this (basically a Destination-Vector algorithm, i.e. like
RIP but with non-static per-hop costs) didn't work too well, for reasons I
won't get into unless anyone cares. The replacement, the first Link-State
routing algorithm, worked much, much, better; but it still had minor issues

damping fixed most of those too).

You're right of course. I was referring more to the fact that changes tended to be an issue.

I always give Dave Clark credit (what I call "Clark's Observation") for the most powerful part of the replacement for the ARPAnet - aka the idea of a network of network. Dave once quipped: "Why does a change at CMU have to affect MIT?" I've forgotten what we did at CMU at the time, but I remember the MIT folk were not happy about it.

> DH11's which were a full "system unit"

Actually, two; they were double (9-slot, I guess?) backplanes.

Right.

> The MIT guys did ARP for ChaosNet which quickly migrated down the street
> to BBN for the 4.1 IP stack.

Actually, ARP was jointly designed by David Plummer and I for use on both
TCP/IP and CHAOS (which is why it has that whole multi-protocol thing going);
we added the multi-hardware thing because, well, we'd gone half-way to making
it totally general by adding multi-protocol support, so why stop there?

Thanks, I never knew that. Makes sense.

As soon as it was done it was used on a variety of IP-speaking MIT machines
that were connected to a 10MBit Ethernet; I don't recall them all, but one
kind was the MIT C Gateway multi-protocol routers.

Thought, didn't you guys have the 3Mbit stuff like we did at CMU and UCB first?

> Hey it worked just fine at the time.

For some definition of 'work'! (Memories of wrapping protocol A inside
protocol B, because some intervening router/link didn't support protocol A,
only B...)

Hey when we did it, we were trying to a UNIX machine to talk to CDC Cyber and an VMS/VAX. No routers. We were happy to just have those systems communicating ;-)

I was not smart enough to see something like ARP - which later seemed like such a D'oh moment.

Then again -- at the time 48 bits of Ethernet was supposed to me "enough" and you were not going to need anything else. Funny how it all worked out.