[Iccrg] Re: [multipathtcp] Please review "Coupled Congestion Control for Multipath Transport Protocols"

[Michael Welzl]

>> - On page 6, when you first introduce alpha, you call it "a  
>> parameter ..
>> that describes the aggressiveness of the multipath flow"
>> (missing "s" in "aggressive" in that sentence BTW).
>> ... so this gives the impression that this is a per-aggregate  
>> parameter.
>> Yet, later, on page 7, you state that "alpha must be computed for  
>> each
>> multipath flow". Indeed I have a hard time imagining how alpha can  
>> ensure
>> that you send at least as much as TCP would send on the best path  
>> while just
>> having a single constant across all sub-flows. So I assume it's a
>> per-subflow-variable - but then it should get an index i.
>> I would strongly suggest giving a simple example where MPTCP is  
>> used across
>> two very different paths, just to show how alpha indeed ensures the
>> throughput of TCP on the best path because that seems to be hard to  
>> grasp
>> with intuition.
>
> Alpha is computed for each connection - the same alpha applies to all
> subflows, so as to control the overall aggressiveness.  It is not a
> per-subflow variable.
>
> Obviously our text is unclear on this - is there somewhere in
> particular that made you think it was per-subflow?  Or is it just the
> wording on page 7 ("alpha must be computed for each multipath flow")
> which could be rephased "for each multipath connection" if that helps.

It's really only this wording. and yes, this simple change does the  
trick - i guess it was just me, the word "flow" made me think of sub- 
flows.

About another sentence I wrote above: "Indeed I have a hard time  
imagining..."  - now I wonder what gave me this hard time? It actually  
seems clear enough.
Still, an example would be nice to have, but I take back the "strongly  
suggest". Sorry, I must have been tired.

Cheers,
Michael