[e2e] A simple scenario. (Basically the reason for the sliding window thread ; -))
David P. Reed
dpreed at reed.com
Tue Jan 23 09:13:39 PST 2007
This is a very strange debate. One can (of course) develop an
idiosyncratic protocol that works in just this case better than any
other protocol. The situation is not "broken" - just highly specific,
the kind of thing that one encounters as a result of historical
accidents, and most of the Internet infrastructure is full of historical
So are we accomplishing anything with this discussion?
I assert that all concerned are quite intelligent people. So if the
debate is just to measure your intellectual manhood against each other,
perhaps a contest like "American Idol" would be a better place than here?
David Borman wrote:
> On Jan 22, 2007, at 4:05 PM, Joe Touch wrote:
>> David Borman wrote:
>>>> This is a contradiction: clearly the splitter needs to keep up with
>>>> receiving small packets at rate or it can't sustain emitting the large
>>>> packets at full speed. If the splitter can do this, then the
>>>> can. The fact that it doesn't means this is (by definition) a patch
>>>> to a
>>>> broken system.
>>> Ah, you are assuming that both the ethernet side and the 64K MTU
>>> side of
>>> the path operate equally efficiently using small packets.
>> source ---------------> splitter ----------------> dest
>> 1500byte 64K byte
>> You're claiming that the splitter is required to keep the 64Kbyte side
>> running at full rate. That means the 1500-byte side has to handle
>> packets roughly 40x faster. Otherwise, the 64K byte side is not running
>> at high-rate.
>> So here's what we have:
>> - dest can handle 64K but not 1500
>> - source must handle 1500 at high rate
>> - splitter must receive 1500 at high rate
>> Now you're claiming that there's a link (source-splitter) that's
>> efficient enough for small packets. If that's the case, why would we
>> ever want the kind of link that's being used splitter-dest?
> If all you're ever going to do is talk through the splitter to remote
> ethernet hosts, then yes, it'd be preferable to bring ethernet
> directly to the host instead of using the 64K MTU network. But you
> don't always get what you want. For various reasons it might not be
> possible to bring ethernet directly to the hosts on the 64K network.
> And while the 64K MTU network may not be as efficient with 1500 byte
> packets as an ethernet network, replacing it with an ethernet network
> might be slower internally than the 64K MTU network. So the trade off
> is a faster 64K network that works well with large packets but not
> ethernet sized packets, vs. a slower ethernet network that works
> better with ethernet sized packets, but doesn't have the overall
> capacity of the 64K network.
>> Again, this argues that something is seriously broken.
> Sometimes there isn't an optimal solution and you have to make hard
> choices. Just because it isn't the one you want doesn't mean things
> are *broken* when you then try to mitigate the effects of those choices.
> -David Borman
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