[e2e] Comparing Linux qdiscs in lab conditions (paper)

Joe Touch touch at isi.edu
Wed Feb 13 12:39:42 PST 2013

On 2/8/2013 4:35 PM, Detlef Bosau wrote:
> Admittedly, I did not follow the whole discussion in its ramifications.
> What I still wonder about, not only in the context of buffer bloat, is
> that I frequently find the claim, the "bottleneck" of a TCP flow would
> be located on edge routers and not on core routers. And that's the
> central point I simply don't buy.
> The question may be often asked, but do we really know, where packets
> pile up and which routers suffer from buffer bloat? Particularly in the
> paper by Van Jacobson and Kathleen Nichols, I find quite some remarks on
> CoDel on edge routers. I simply see no sense in placing AQM algorithms
> on edge routers. When I, living in Stuttgart, download a huge file from
> some server in Boston, it is almost sure that my ADSL router is
> definitely not the bottleneck.
> Generally, when queues grow too large on core routers, why don't we
> manage queues there?
> Perhaps, this is a general misconception of mine, however: why don't we
> fight buffer bloat where it occurs?

FWIW, bufferbloat examples I've seen tend to focus on *upload* out of 
the home. As you note, download isn't the issue as much.

Try this:
	- upload a video to youtube (or anywhere)
	- ping somewhere else

That can happen within a single machine (that was the first case I heard 
about, and as anticipated the issue was in-kernel buffering) or between 
two machines (if the home router has too much buffering and too little 
brains to do proportional sharing).

Less buffering - either in the OS or the router - sometimes helps reduce 
delay because the greedy application backs off (due to losses), is 
scheduled to transmit less often (when on the same machine), or simply 
loses more packets.


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