Fwd: [LARTC] HTB Weird Shaping Question(Bug?). Please Help!

From: Leo Huang <leo.maillist@gmail.com>
To: lartc@vger.kernel.org
Subject: Fwd: [LARTC] HTB Weird Shaping Question(Bug?). Please Help!
Date: Wed, 27 Apr 2005 00:47:53 +0000	[thread overview]
Message-ID: <8f60055e05042617472423ecb9@mail.gmail.com> (raw)

Oops, forgot to post to the group...

---------- Forwarded message ----------
From: Leo Huang <leo.maillist@gmail.com>
Date: Apr 27, 2005 10:46 AM
Subject: Re: [LARTC] HTB Weird Shaping Question(Bug?). Please Help!
To: Andy Furniss <andy.furniss@dsl.pipex.com>

Thanks Andy,

What you have said makes absolute sense to me. However, I only
"reserved" 136Kbit for the VoIP traffic, there are 44Kbit available
even we assume the 180Kbit is the maximum. Why doesn't HTB allocate
the 44Kbit to the class for ping traffic, which only require rate
4Kbit and 0.5 Kbit?

Thanks again,
Leo

On 4/27/05, Andy Furniss <andy.furniss@dsl.pipex.com> wrote:
> Leo wrote:
>
> > In the first test, I limit the SUBCLASS_OUTRATE to 200Kbit. Both pings
> > are around 20ms before I start the VoIP services. However, once I start
> > the services, the pings jump up to 1800ms.
> >
> > In the second test, I limit the SUBCLASS_OUTRATE to 180Kbit. The pings
> > jump up to 80ms, which is perfectly acceptable.
> >
> > After a few tests, I noticed that 180Kbit is a magic number, anything
> > exceed that will generate 1800ms pings, and below it is 80ms.
> >
> > In my senario, the weird point is that the determining factor is the
> > ceiling, but not the rate. That's the "rate" for other class doesn't
> > seem to give bandwidth to packets in the corresponding class unless the
> > ceil for the 1:110 is low enough!
> >
> > I attached my script and "tc -s class show" below. I truncated part of
> > the script and the results to make it short.
> >
> > Please shine me a light!
>
> It's because the link is dsl and there are lots of overheads on each
> packet (and they vary with packet size). HTB rates are based on ip
> packet length and with lots of small packets like voip the difference
> can be alot.
>
> The 1800ms latency is not caused by a queue within htb it's in your
> modem/router because it can't send >180kbit ip level for voip.
>
> You can patch HTB and TC to make things perfect - you could set a ceil
> very close to your sync rate then. You need to know exactly what type of
> dsl you are on to find your overhead though. If your modem/router gives
> ATM cell counts you can deduce it from those.
>
> There is a very good thesis and patch info here -
>
> http://www.adsl-optimizer.dk/
>
> Andy.
>
>
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