List Receiver wrote:>For those of you in the US using Comcast as your ISP, you''ll know
that
>they now have a feature called Powerboost available in the regions they
>serve. Basically, it allows people to have higher-than-rated throughput
>for the first few minutes of data transfer. After those few minutes,
>they''re supposed to throttle back down to what their rated line
speed
>is.
>
>I''m having difficulty coming up with a solution to do traffic
shaping on
>these kind of connections. Since the line speed isn''t fixed, my
guess
>was to set the traffic shaper to use the maximum possible speed as
it''s
>downstream limit.
The only way to make it work reliably is to set your up and down
speeds in the traffic shaper to be the throughput that the line is
guaranteed to handle all the time. Eg, if you have a nominal 1M down,
but the system allows 2M for a few minutes, then you would need to
set you traffic shaping at a little under 1M.
If you set it at (a little under) 2M, then it will work fine for a
bit, but then you will lose all the benefits of keeping the upstream
queue empty once you get throttled down. Ie, you will be throttling
down to 2M, but the line is throttled by the ISP to 1M, hence the
upstream buffer will fill up and your latency goes up.
> I guess I have a couple questions, more on the
>conceptual level:
>
>1) Is there a way to remove all traffic shaping from the inbound channel
>of an interface...given you can''t really do that anyway? Does
setting
>the bandwidth value too high effectively do this?
Yes
>2) By setting the bandwidth values for the WAN interface abnormally
>high, will the traffic shaper still re-order the packets as they leave
>the interface on the upstream channel?
>
>I would think that if tc could simply re-order packets, with a small
>queue maintained for lower priority traffic, then the throughput limits
>would not have to be defined...allowing the shaper to rise and fall with
>the Powerboost oddness. This idea is wholly unfounded, however, so
>please illuminate me.
The problem is that (normally) between you and the line is a router,
normally a cheap and nasty thing with no concept of prioritisation.
Unless you pass packets to it at a lower rate than the line will
handle, then it will build up a queue and you will lose the benefit
of the shaper.
If you are directly connected to the line (ie the modem is in the
firewall) then in principal the OS should be capable of feeding the
packets from the high priority queue first.
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