Re: TCP window based shaping

Linux Advanced Routing and Traffic Control

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On Sat, Feb 12, 2005 at 02:16:09AM +0000, Andy Furniss wrote:
> 
> >Are we all on the same page as to what the problem is?  Any more
> >thoughts on how to tackle it?  I'm still not convinced that delaying
> >ACK's is really any better than the current option to buffer incoming
> >data.
> 
> I suppose the gain for marco is that he will not just be delaying acks - 
> OK he could do the same for data and I agree that there isn't much 
> difference and it could be better to work with date in some ways eg. you 
> can really drop whereas with acks it would be harder to simulate a drop.

note that drop means 'losing correct data already received'. so when we
drop, we need a retransmission, so we are wasting bandwidth. 

btw, simulate a drop is easy just send two (or three - it depends on the
implementation of the tcp stack) duplicate ack that means: we have received
out of order packet so please retransmit.
 
> I don't think he will be just buffering though - thats the advantage for 
> him - to build in intelligence to handling the problem of shaping from 
> the wrong end of a bottleneck without the handicap of using dumb queues 
> that are seeing traffic that's allready shaped by a fifo and whose fill 
> rate is determined by what percentage of the fifo rate you set their rate.

yes, that's the idea. 
 
>   I guess the receiving machine TCP stack gets it earlier so the
> >app looks more responsive, but other than the lower lag I don't see much
> >difference really?
> >
> >Curious to hear how your project gets on though!  Please keep us informed!
> 
> Me too - Thomas Graf is also playing with delaying acks - see the dummy 
> replacing imq thread this & last month on a netdev archive.
>
> I also remember seeing another shaper that uses delay pools for acks 
> bandwidth arbiter or arbitrator IIRC. If you can't find it say, I 
> probably have it squirreled away somewhere on my old PC.

thank you for those references. 

ciao ciao.

-- 
BOFH excuse #270:

Someone has messed up the kernel pointers
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