Thank you all,
I'm reading carefully, because I don't understand at first :)
Regards
On Sat 12 Jan 2013 02:04:00 AM ICT, Sebastian Moeller wrote:
Hi there,
On Jan 11, 2013, at 05:16 , Brian J. Murrell wrote:
On 13-01-11 07:29 AM, [email protected] wrote:
Hi
http://wiki.openwrt.org/doc/howto/packet.scheduler/packet.scheduler
Note that OP described wanting to distribute "download" bandwidth for
users. The document you posted above is about shaping "upload" bandwidth.
As the above document states, one cannot really "shape" download
bandwidth but can only "police" it by dropping packets as they come in,
and then, that only works for TCP and not UDP.
I wonder about whether that is actually right. Looking at the
definitions of shaping and policing it is quite clear that in the real world
any shaper will also police (and if only by virtue of limited buffers at one
point packets will be dropped, turning a shaper into a policer). Adding a
shaper to san ingress policer offers the following advantage: the developing
queue, especially if the queueing is per flow or close to per flow (as in a
number of different queueing disciplines available) will give the policing
component more information to pick which packets to fro or mark. Thus in the
real world shaping can be considered, as a fancy way of policing, so any shaper
will fall back being a policer (worst case scenario all buffers are filled and
a new packet arrives).
Neither shapeing nor only policeing will be able to help against an
inelastic UDP flood on the downstream. Especially if said flood consumes all
link's bandwidth so even if the receiver drops all UDP packages no real traffic
will make it through the bottleneck. This can only be solved on the head-end of
the downstream; but inelastic UDP traffic is quite uncommon outside of DOS
attacks, so this has nothing to do with the question of to shape or not to
shape.
Where shaping will help is if several (longer-running) TCP flows compete the
downlink, then shaping can help to distribute the speeds of these individual flows to
"fairly" share the downstream bandwidth (depending on your shaper setup and
definition of fair).
All of these facts (if actually) true seem to make the argument for using a
shaper not a policer even on the remote end of a "bottle-neck" link like a
typical cable/dsl/lte connection. Now, I could be just full of it, so please show me
where my reasoning is off, and why policing is better than shaping.
best
Sebastian
b.
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--
Regards,
Quân
Y!IM: ng_hquan_vn
GTalk: ng.hong.quan
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