To what extent will WPA reduce throughput? and the cause of this reduction?
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From: Barb Bowman on 27 Mar 2008 05:22 what wireless router are you using? On Wed, 26 Mar 2008 21:03:59 -0700 (PDT), MingChingMin(a)yahoo.com.hk wrote: >1. To what extent will WPA reduce throughput? >2. Which factor dominates this reduction, computation loading or >bandwidth overhead? > >With my wireless LAN, I do not feel any degradation to throughput when >running WEP64 or WEP128. When I run WPAPSK, the throughput is reduced >by 40% on transferring large files. I would be grateful to know if >this is a common phenomenon, or it just happens to my site. > >Then I make attempts to find out what has caused this reduction in >throughput. I have gone through the following experiments, but have >difficulties in interpreting the results. > >In my experiments, an 8 MB file is transferred from Computer A to >computer B. Computer A is connected by UTP to a port (not the WAN >port) of a wireless router. Computer B is equipped with a wireless >adapter. Computer B reads the 8 MB file and sends it to Computer A. >Computer A receives the file, reports the speed but does not write the >file to harddisk. This is done to minimize the impact of disk >performance to out experiments. At the mean time, I monitor the >networking performance and CPU utilization at "Windows Task Manager". >Both computers runs WinXP with hyperthreading CPUs. The following >shows my experiment log. > >(1) Wired connection, B sends to A: >Sender: >networking: peaks at 62.5% of 100Mbps >CPU: peaks at 9% >receiver: >networking: peaks at 45% of 100Mbps >CPU: peaks at 12% >Throughput: 94 Mbps >It seems that the reading of the file form disk is not a bottleneck in >my experiment. > >(2) Wireless connection without wireless security protocol >Sender: >networking: peaks at 50% of 54 Mbps >CPU: peaks at 16% >Receiver: >networking: peaks at 28% of 100Mbps >CPU: peaks at 11% >Throughput: 26Mbps >It seems that the wireless adapter is running close to its theoretical >maximum. > > >(3) Wireless connection with WEP64: >Sender >networking: peaks at 50% of 54 Mbps >CPU utilization: peaks at 13% >Receiver: >networking: peaks at 7% of 100 Mbps >CPU : peaks at 9% >Throughput: 26Mbps >It seems that no degradation of throughput is caused by WEP64. > >(4) Wireless connection with WEP128: >Sender: >networking: peaks at 50% of 54 Mbps >CPU: peaks at 40 >Receiver: >networking: peaks at 27% of 100Mbps >CPU: peaks at 8% >Throughput: 26Mbps >No degradation to throughput by WEP128 either. > > >(5) Wireless connection with WPAPSK: >Sender: >networking: peaks at 37.5% of 54 Mbps >CPU: peaks at 21% >Receiver: >networking : peaks at 16% >CPU: peaks at 14% >Throughput: 16Mbps >My difficulties lie here! networking performance is not at the >expected 50%. Could it be because the computation work for encryption >is not done fast enough to allow data be pumped out at ceiling rate? >But CPU utilization is far less than 50%, the ceiling for one >hyperthread. Could it be because the encryption is done in the >adapter? But it is only an inexpensive USB wireless adapter, even >without WPA2 capability. Could it be that actually the wireless raw >data throughput has reached ceiling, but Windows Task manager only >reports the throughput of data stream before encryption? In that case, >the encrypted data is 33% larger than the plantext. But WPA uses RC4 >stream cipher so it is unlikely that the ciphertext is 33% larger in >size than the plaintext. What has really happened? Please give me some >advice. > >P.S. >About my understanding that Windows Task Manager sees a one way >traffic at ceiling rate as 50%, I got it from the following >experiments. Please tell me if my understanding is wrong. > >(6) Wired connection, both computers send and receive at the same >time: >No significant difference between the two streams is observed. >Both computers: >networking: peaks at 100% > >(7) Wireless connection, no encryption: both computers attempts to >send and receive at the same time: >It is observed that the two ways are asymmetric. The traffic from the >wireless adapter to the wireless router has significantly higher >priority, although the other stream also makes progress. Throughput >from B to A is 21Mbps, and that from A to B is 6 Mbps. After the B to >A sending has finished its 8 MB file, the A to B traffic resumes its >performance at 26 Mbps. >Computer A network utilization: peaks 27% of 100Mbps >Computer B network utilization: peaks at 50% of 54Mbps > > >Please give me some advice. -- Barb Bowman MS-MVP http://www.microsoft.com/windowsxp/expertzone/meetexperts/bowman.mspx http://blogs.digitalmediaphile.com/barb/
From: Barb Bowman on 28 Mar 2008 05:29
are the results different when you set the router to "g only" mode? mixed b/g is slower because the specification calls for it to stop and wait for b traffic. On Thu, 27 Mar 2008 18:55:26 -0700 (PDT), MingChingMin(a)yahoo.com.hk wrote: >The wireless router used: >Manufacturer: Level One >Model: WBR-3406TX >It supports 802.11b/g >The USB wireless adapter used: >Manufacturer: Level One >Model: WNC-0301USB >It supports 802.11b/g > >In these experiments, the wireless adapter is placed within 10 cm from >the wireless router. -- Barb Bowman MS-MVP http://www.microsoft.com/windowsxp/expertzone/meetexperts/bowman.mspx http://blogs.digitalmediaphile.com/barb/ |