Date: Wed, 30 Nov 2011 07:37:48 -0500 From: "Viet-Ha Pham" <hapvbk@yahoo.co.uk> To: <freebsd-net@freebsd.org> Subject: Wifi throughput test issue (FreeBSD 8.2) Message-ID: <69C75F6ECC9646C79374299EDF0E4304@PC>
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Hello, I am doing some throughput measurement for Wifi network. I am using = jperf/iperf to generate traffic (at the transmitter) and measure the = throughput (at the receiver). The transmitter and receiver are running = FreeBSD 8.2, using CM9-GP as the Wifi NIC. We are testing AWGN channel. = So, the transmitter and receiver are connected by cables, txpower on = both sides is set lower than the max (ranging from 0 to 10), AWGN noise = is injected in the middle of the cable.=20 We measure the maximum throughput at each transmission rate. Transmitter = is a STA, receiver is an AP. We fix the unicast rate at the transmitter = to 54 Mbps (using "ifconfig ... ucastrate" command). The packet size is = set to 400 Bytes, UDP protocol is used and the transmit bandwidth is set = to 30 Mbps in order to flood the transmission channel (to push it to its = limit). At first, at the receiver (AP) the measured throughput is about = 12 Mbps. Then I fix the unicast rate at the receiver (using ifconfig = again) to 54 Mbps. The measured throughput increases to 20 Mbps. I set = the unicast rate at the receiver to autoselect again, the throughput is = still 20 Mbps.=20 When I switch the rate at the receiver, there are multiple message = displayed on the screen of the transmitter: "wlan0: = ieee80211_new_state_locked: pending RUN -> AUTH transition lost". This = message is repeated for many times (at least 20).=20 I repeated the test with all transmission rates, change the packet size = and still observe the same thing: a throughput improvement of about 30% = is observed when I switch the unicast rate at the receiver and the = improvement is still there when I switch the unicast rate back to = autoselect. The same thing is observed in modes a and g. The same thing = is observed if the unicast rate at the receiver is set different from = the unicast rate at the transmitter.=20 I spent time to look at the kernel source codes but I did not find a = solid answer for this. Please help me to identify the problem and the = answer.=20 My question is:=20 1. Why do I have that throughput improvement when I switch the rate like = that?=20 2. Is it a bug in the driver?=20 3. What does the error/infor message on the transmitter mean?=20 Thank you so much.=20 HAPV
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