[e2e] A simple scenario. (Basically the reason for the sliding window thread ; -))

David Borman david.borman at windriver.com
Mon Jan 22 13:33:33 PST 2007

On Jan 22, 2007, at 11:09 AM, Joe Touch wrote:

> David Borman wrote:
>> Joe,
>> You keep missing the point.  The delay*bandwidth between the end  
>> hosts
>> is sufficiently large that it can not be driven at full speed from
>> end-to-end given the window advertised by the host on the ethernet  
>> side
>> of things.  Even if that host advertised a sufficiently large window,
>> the inefficiencies of small packets on the 64K MTU side of the  
>> network
>> will keep the network from being driven at full speed, not to mention
>> the cost of ramping up slowstart using 1.5K byte packets vs. 64K byte
>> packets.
> 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.  That is  
not the case.  The splitter isn't able to keep the pipe full over the  
64K network using 1500 byte packets, but it can using larger packets,  
so the further remote host is even less able to keep it full using  
1500 byte packets.  It's like using dump trucks to haul individual  
wheelbarrow size loads; it'll work, but you won't be very efficient  
and the transfer will take a lot longer.

So, I disagree with your contention that the system is broken.  It's  
different and heterogeneous, but that doesn't make it broken.

			-David Borman

More information about the end2end-interest mailing list