[TUHS] Early Unix Spider network

Paul Ruizendaal pnr at planet.nl
Mon May 29 19:54:48 AEST 2017


> The people working on TCP/IP did know of the Spider work (like they knew of
> the Cambridge ring work), but it didn't really have any impact; it was a
> totally different direction than the one we were going in.

I'm aware of that, and I think it was the same the other way around. My
interest is tracing how the networking API of Unix developed in the very
early days, and that's were there is a link.

When I asked a few months back why Bell Labs did not jump onto the work
done at UoI, Doug observed that the lab's focus was on Datakit and that
triggered my interest.

>>>> it turns out that the TIU driver was in Warren's repo all along:
> 
> V4?! Wow. I'd have never guessed it went that far back.

My current understanding is that Spider development began in 1969 and
that it was first operational in 1972. By '73/'74 it connected a dozen
computers at Murray Hill and Unix had gained basic network programs.

From Sandy Fraser's "Origins of ATM" video lecture I understand that the
Spider learnings included that using a mini to simulate a switch/router
was too slow and too costly, and that doing flow control inside the network
induced avoidable complexity (I guess Fraser/Cerf/Pouzin all learned that
lesson around the same time). The follow-on, custom designed Datakit switch
was to correct these issues.

Work started in 1974 and I guess that prototypes may have been available
around 1978 (when Spider was apparently switched off at Murray Hill).
By 1981 a multi-site Datakit network connected various Bell labs and by
1983 Datakit was introduced as a commercial service.

As to the Spider network API, it currently seems that it was relatively
simple: it exposed the switch as a group of character mode devices, with
the user program responsible for doing all protocol work. Interestingly,
Spider used a high speed DMA based I/O board (DR11-B), whereas the
Datakit switch was apparently connected to a low speed polled I/O board
(DR11-C).

I did not find the Datakit device driver(s) in the V7 source tree (only a
few references in tty.h), so it is hard to be sure of anything. However,
it seems that in V7 the Datakit switch was used as "a fancy modem" so to
speak, supporting the uucp software stack.

There is source for a Datakit driver in the V8 tree, but I currently
have no time to study that (and perhaps it is beyond my scope anyway).

All input and corrections much appreciated.




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