Gilbert Saint-Flour wrote:
The last three examples were sponsored (or developed) by IBM, and many
IBM competitors supported the non-IBM solution precisely because it was
that, non-IBM. In the case of Micro-channel and OS/2, licensing issues
didn't help with PC companies like Compaq and HP.
TR also got a lot of bad press because a single PC could wreak havoc on
the ring simply because it was configured for 4 Mb/s instead of 16
Mb/s, and finding the culprit was sometimes quite a challenge.
Ethernet, of course, had a lot of problems of its own, but it didn't
have this one.
there are a whole bunch of issues.
as part of the SAA terminal emulation strategy,
http://www.garlic.com/~lynn/subnetwork.html#emulation
the T/R cards were built with per adapter thruput targeted at the
terminal emulation market segment (say 300 PCs on the same ring).
austin had designed & built their own 4mbit t/r (16bit isa) for
workstation environments. for rs/6000 they were forced to use the
corporate standard 16mbit microchannel t/r card. this card had lower per
card thruput than the pc/rt 4mbit t/r card (they weren't allowed to do
their own 16mbit microchannel t/r card that had even the same per card
thruput as their 4mbit 16bit ISA t/r card).
as part of moving research up the hill from sjr to alm, the new alm
building had extensive new wiring. however, in detailed tests they were
finding that 10mbit ethernet had higher aggregate thruput and lower
latency over the cat5 wiring than 16mbit t/r going over the same cat5
wiring.
in the SAA time-frame we had come up with 3-tier architecture
http://www.garlic.com/~lynn/subnetwork.html#3tier
and were out pitching it to customer executives .... including examples
showing 10mbit (cat5 wiring) ethernet deployments compared to 16mbit t/r
deployments (using same cat5 wiring).
we were taking lots of heat from SAA forces which were actively trying
to contain 2-tier/client-server and return the paradigm to the terminal
emulation from the first half of the 80s (so you didn't need faster per
card thruput because you were stuck in terminal emulation paradigm and
you were stuck in terminal emulation paradigm because of the limited per
card thruput).
we were also taking lots of heat from the t/r contingent. one of the t/r
centers had published a paper showing 16mbit t/r compared to "ethernet"
... with ethernet degrading to less than 1mbit aggregate effective
thruput. it appeared to be using the ancient 3mbit ethernet
specification which didn't even include listen before transmit (part of
the 10mbit standard).
about the same time, annual acm sigcomm had a paper that did some
detailed look at commoningly deployed ethernet. one of the tests had 30
stations in tight low-level device driver loop transmitting minimum
sized packets as fast as possible. In this scenario, effective aggregate
thruput of 10mbit ethernet dropped off to 8.5mbits from a normal
environment with effective aggregate thruput of 9.5mbits.
disclaimer: my wife is co-inventor for token passing patents (US and
international) from the late 70s.
----------------------------------------------------------------------
For IBM-MAIN subscribe / signoff / archive access instructions,
send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO
Search the archives at http://bama.ua.edu/archives/ibm-main.html
