[e2e] TCP Loss Differentiation

Jon Crowcroft Jon.Crowcroft at cl.cam.ac.uk
Mon Feb 23 15:37:08 PST 2009

its a thought experiment - you don't implement thoguht experiments -
the point is to illustrate why not. i'm not attacking ECN _ what I am
pointing out is purely a response to the idea that you cannot tell, on a
per packet basis,  in any affordable way, that a loss was caused by congestion
or otherwise - there's an information theoertic argument fighting to
get out here... ( I suppose i could start to quote your last
governments leaders "known unknowns and unknown unknowns" if I wanted
to be annoying, but I wont)

I'm not being sarcastic so dontbe so to me.

In missive <8D67D867-C4F4-43CC-B76A-795F78D72FDD at cisco.com>, Fred Baker typed:

 >>On Feb 23, 2009, at 3:01 PM, Jon Crowcroft wrote:
 >>> if each router were to record in every packet in a flow, all the  
 >>> packets it had seen, the order it had seen them, and the routers own  
 >>> address, then when any packet arrives, you'd have a cmplete history  
 >>> of packets predeceessors and successors and gaps, and where gaps are  
 >>> caused, and so a receiver can disambiguate on a _per packet_ base  
 >>> when a loss was not congestive...
 >>Great! I'm really excited to hear that every router has now sprouted a  
 >>reason to add a few more gigahunks of memory, and that service  
 >>providers are willing to pay the operational expense in heat and  
 >>power! My product managers will be truly dumbfounded that they had not  
 >>tumbled on that source of revenue in the past. And I'm sure that the  
 >>ISPs will be all too eager to pass the upgrade cost along to their  



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