From owner-freebsd-hackers@FreeBSD.ORG  Wed Feb 18 19:39:47 2009
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From: Mel <fbsd.hackers@rachie.is-a-geek.net>
To: freebsd-hackers@freebsd.org
Date: Wed, 18 Feb 2009 09:48:04 -0900
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Cc: Bruce Cran <bruce@cran.org.uk>, xorquewasp@googlemail.com
Subject: Re: Simulating bad network conditions
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On Wednesday 18 February 2009 01:39:03 Bruce Cran wrote:

> It seems ALTQ can't delay packets though, so you'd need to use dummynet
> for that.

You can work around it using hfsc's realtime:
hfsc(realtime (0Kb 300 128Kb))
   1.  0Kbit of bandwidth guaranteed for the first 300ms
   2. After 300ms 128Kbit of bandwidth is provided
   3. When using this method, the first value must be 0.

Though, this only works when under pressure. If enough bandwidth is available, 
the delay won't happen.

More info here:
http://www.probsd.net/pf/index.php/Hednod%27s_HFSC_explained

-- 
Mel