[e2e] What's wrong with this picture?
David P. Reed
dpreed at reed.com
Fri Sep 11 08:29:38 PDT 2009
Perhaps I was not clear. I REALLY think Dimitri's comments about why
the layer 2 stuff might have huge delays with perfect reliable delivery
are really good starting points for exploring how to design a good
implementation of HSPA packet transport at layer 2, where "good" means -
works well for an Internet Access Network.
I want to thank him for putting in that useful information (I have no
ability to reach inside ATT's corporate proprietary wall to do those
experiments. But on the other hand, the phenomenon is observable and
reliable, with more experiments possible even without ATT cooperation).
At the same time, it's important to realize that layer 2 is not "unto
itself" the system requirement specifier.
Scott Bradner told me that it is common for ISPs to write contracts to
layer 2 equipment vendors that state "Never drop packets". If it's in
the contract, the blame switches back to the ISP that wrote the contract
for buying the wrong stuff. (though I'd suggest that if the layer 2
vendor knows that his customer will be running IP over it, he might
*counterpropose* a *better* system).
Ultimately, I hope that AT&T resolves this problem somehow. It may cost
a lot of money. Intel eventually fixed the floating point bug in the
Pentium, rather than try to cover it up by a PR blitz. That was the
right decision - but since I was involved, I know from personal
experience that engineers at Intel and its customers were under enormous
pressure to agree with the Intel PR people that "no user would ever
experience the bug". It took a Lotus 2-cell spreadsheet, with simple
formulas any ordinary person could understand, that gave an answer off
by a factor of 10, to demonstrate that "any user could see and
demonstrate the bug".
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