On Nov 8, 2021, at 11:09 AM, Robert Armstrong <bob
at jfcl.com> wrote:
"when do you send the message".
That's actually a question with TCP as
well...
You know about the Nagle algorithm, right?
Bob
Yes, that's what I was talking about.
As for OSI not producing anything, that's not entirely true. OSPF is clearly derived
from at early draft of IS-IS, however much its authors may want to hide that fact.
The people in the DECnet architecture group (I was one, though junior) certainly went
through a whole lot of hindsight review over the OSI vs. TCP history. It's always
easy to say the right answer was obvious when you look back a decade or three later after
everything was settled. At the time, it wasn't quite so obvious.
The US centric vs. international thing is clearly a piece of the puzzle. Another piece is
that, other than for academic and military use, the ARPAnet wasn't really available.
Once it opened up for commercial use the matter was settled, but that didn't happen
until later (around the time of the invention of the world wide web). So at the time
Phase V was being created, the world had lots of small islands -- individual company
in-house networks -- with very little interconnectivity among them. And in much of the
world, what cross-company connectivity existed was, often by law, provided by phone
companies. Those were very much invested in X.25 andd its various spawns. OSI was early
on a generalization of X.25. The fact that it came to support datagram service, such as
the TP-4 transport and connectionless network layer protocols like ISO 9542 (?) is in
large part due to DEC pushing for it to be not quite so much "X.25 on steroids".
That also tells us that DEC decided on a "help the Telcos make OSI not be so
broken" rather than "ignore the telcos and do it some other way" which
would have been hard to pull off outside the USA where it's telcos or nothing. (I
remember a DEC Ethernet bridge with a Swedish telco approval sticker. It turned out that
at the time in Sweden you could not run your own wiring between floors in your own office
building: such cross-floor connectivity was the monopoly of the government telco.)
Last but not least, Phase V was a long running effort. A few bits of it are visible in
Phase IV (the weird stuff in the "long data header"). By the time I joined the
DNA group in 1984 it was already well underway, but products didn't actually ship for
several years afterwards. The landscape in 1983 was rather different from that of 1990.
Data links had some of the same sort of stories. We now know that Ethernet beat
everything else, but early on that wasn't so clear. The effort to defeat IBM token
ring (802.5) took a long time. I helped write a long DEC document (40-60 pages?), the
DEC-3Com reply to IBM Document xyz-nnn, a pile of FUD and baloney about the
"superiority" of the IBM token ring.
There was also 802.4, a GM contraption created because of the notion that Ethernet
wasn't "real time" enough. 802.4 does have bounded latency that (half
duplex) Ethernet doesn't, but the bounds are so high that it doesn't actuallly buy
you anything. The only merit of 802.4 is that it is the foundation of FDDI. (No, FDDI
has *nothing* to do with 802.5, other than the words "token" and
"ring".)
I still remember when we at DEC were busy building FDDI products and one of my colleagues
(most likely the manager, Bill Hawe) asked somewhat tongue in cheek "could we just
run Ethernet at FDDI speeds?". It didn't take more than a few hours to conclude
that the answer is "yes". Even so, when that effort got underway, HP tried to
wreck it by a bizarre 100 Mb/s vaguely Ethernet-like protocol. In the end that didn't
go anywhere and regular Ethernet took over everywhere.
paul