Date: Tue, 06 May 2008 15:03:43 -0400 From: Matthew Pope <mpope@oanda.com> To: freebsd-ipfw@freebsd.org Subject: dummynet queue size relative to bw setting? Message-ID: <4820AB8F.2000204@oanda.com>
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Hello, I've been reading about dummynet for 2 weeks, including the seminal ACM paper & I'm very impressed. I've configured and run some preliminary simulations that have my colleagues quite interested too. However, I'm finding my delay settings are yielding delays of about two orders of magnitude larger that requested. I believe I don't understand the relationship very well that defines the setting of the queue size to relative to the bandwidth setting (and plr?) Can someone explain or point me to a source for this? I recall reading that with lower bandwidths one should use lower queue sizes to avoid long queuing delays. So I presume that is why my delays are so long. So I've run some tests with various queue sizes. With Queue sizes of 100, 80, 60, 40, 10 slots on a pipe with a bw of 48Kbits/s, delay of 5ms, and plr 0.025 defined in each direction, I'm consistently getting RT delays of 500-600ms with a ping test, packet loss does come out around 5%. The target I'm pinging is normally a 40 ms latency. At Queue size 120 I get 100% packet loss (but I can ignore that). I am not a networking specialist, so I realize my question is ignorant :-) I'm running this in VMWare Server on a dual core 2 GHz with 2 GB RAM using a modification of the dummynet test network design described at codefromthe70s.org Thanks, Matthew
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