[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 
>>>> destination
>>>> 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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