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

[Mark Handley]

On 24 January 2011 05:23, Michael Welzl <michawe at ifi.uio.no> wrote:
> Hi,
>
> Here's my review:
>
> This is, on the whole, a very well written document - short and concise, and
> clear and to the point. I noticed just a few issues:
>
>
> - 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.

 - Mark