[e2e] TCP Loss Differentiation

[Detlef Bosau]

Jon Crowcroft wrote:
> hmmm - do you want the CS answer or the EE answer
>
> i think the CS answer is that you can't differentiate 
> congestion from failure causes for loss on a per packet basis 
>
> thought experiment - what if a packet that is ECN marked gets lost?
>   

...then the ECN mark is lost as well :-)

That's the very strenght of implicitely signalling congestion by packet 
loss: loss cannot get lost :-)

> i think the EE answer is that you could infer the likely cause
> from the statistics of the channel over the recent past. of course, it
> may be easier to do this at a receiver than a sender.
>   

So, you make a maximum likelihood decision, correct? Of course, such a 
decision may be wrong.
Hence, I personally tend to the CS answer ;-)

>
> in multihop radio networks (especially if you have multipath routing), 
> there is even a problem statistically
> dis-ambiguating packet loss due to congestion and interference, since
> some intererence is due to other packets on parallel flows that go
> over "links" that are near enough (even on "link disjoint" routes)
> to cause interference...(think "rubbernecking")
>
>   

When I wrote my first post in this thread, I intentionally did not 
consider multipath routing on network layer.
I well consider multipath routing on physical layer. More precisely, I 
thought of networks like HSDPA, which don't support soft handover to my 
knowledge.
In UMTS networks with soft handover, the situation may be different of 
course.

And not only different, but interesting as well, because multipath 
routing on network layer may result in different routes with different 
capacities as well....

Now, I have written some brainless stuff on this matter and submitted it 
somewhere.... And thinking about this, I'm curious whether I will get a 
remark on this one by the reviewers ;-)


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