> On Apr 12, 2022, at 3:45 PM, John-Paul Stewart via cctalk
> <cctalk@classiccmp.org> wrote:
>
>
> On 2022-04-12 09:49, Paul Koning via cctalk wrote:
>>
>> Does anyone still remember the other 100 Mb Ethernet-like proposal, I
>> think from HP, which added various types of complexity instead of simply
>> being a faster Ethernet?
>
> HP's proposal was called 100BaseVG, aka 100VG-AnyLAN, and could carry
> Token Ring frames in addition to Ethernet.
Ah, that would certainly be one part of the explanation why it didn't go
anywhere. Supporting Token Ring would add a vast amount of complexity for no
real benefit.
I noticed the Wikipedia article has a wrong and misleading description of the
supposed "deterministic" behavior of token rings. It speaks of "consistent
performance no matter how large the network became". That, of course, is
nonsense. What is true is that, in the absence of errors, token rings have a
hard upper bound on the time required to transmit the first frame in the NIC
transmit queue. What is always unstated in the marketing documents making that
claim is how large that upper bound is.
I remember an IBM document that spent 30 or so pages saying "token ring good,
ethernet bad". DEC, with some help from 3Com, wrote a detailed paragraph by
paragraph refutation of that; I participated in creating that and have a copy
somewhere. One of the points IBM made was that determinism claim. So we
calculated the worst case transmit latency for a max size 802.5 ring. I don't
remember the answer exactly; I'm pretty sure it was over a minute.
FDDI is an entirely different protocol, with dramatically better latency at
high load than 802.5. (Its ancestor is 802.4, not 802.5.) But even there, the
max latency is surprisingly long.
Ethernet, on the other hand, is nondeterministic (in the half duplex shared bus
topology) but except at insanely high loads is much lower than the latency of
any token ring.
paul
