Wireless: What is the maximum throughput of wireless? This FAQ isn't directly related to pfSense, rather it applies to wireless on all platforms, from any vendor. Jim Thompson (netgate.com) posted the following (with some edits from me) to the list on December 2, 2005. The overhead in wireless isn't limited to beaconing and CSMA/CA. The largest 'overhead' is that the 802.11 MAC can't keep the air "full". There are delays due to turn around (for ACKs), overheads due to the preamble and headers, etc. 802.11g has a further requirement for "protecting" existing 802.11b clients by sending a CTS frame prior to sending the data frame (though this can be disabled). In theory (and I stress *theory*) the performance of 802.11's PHYs over TCP, with 1500 byte frames (802.11 allows larger frame sizes, but Ethernet does not) expressed in terms of maximum thoughput for a single pair of stations (or a STA and an AP, if you prefer) looks like this: 802.11b: 5.6Mbps 802.11a 27.3Mbps 802.11g (no protection frames) 27.3 Mbps 802.11g (with CTS protection frames) 13.0Mbps And, you'll find that as you add users to an AP, the throughput does not fall-off linearly with each new associated station. In theory the 'turbo' modes can get you 2X this, but sending twice the signal through the PA means that not only does tx power get pulled back, but the rx sensitivity drops, and the likelyhood of an error sufficient to destroy the modulation envelope goes up as well. You will find that you can't get as many frames through (undamaged) running 'turbo' as you can with the same "standard" modulation rate. 802.11e offers an alternative MAC which can eliminate some of the 'dead spaces' in 802.11's standard DCF MAC. This can increase performance quite a bit. (And, in keeping this "on" the subject of pfSense, pfSense should be able to support this newer MAC, though I need to go see if there is a way to enable it.) The Atheros chipsets also support compression of the datastream, and something called "fast frames" where the intra-frame protocol is changed to reduce overheads as well. If you put it all together, and have near-perfect conditions, (and the moon is in the correct phase) a pair of Atheros cards can stream data (say, a ton of zeros) back and forth around 90Mbps using TCP. Cut the compression out and this falls to around 65Mbps. Cut turbo and this falls to around 33Mbps. See above for throughputs without frame bursting and "fast frames". Of course, at short range required to actually see 90Mbps, you might as well use an Ethernet cable. The real news here is that, with a bit of work (say to add the 4-address frame support that madwifi currently enjoys) pfSense should be able to 'bridge' across wireless with 30Mbps or more at Page 1/2 (c) 2007 <> URL: http://faq.pfsense.org/index.php?action=artikel&cat=12&id=112&artlang=en

WiFi Troughput

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Wireless: What is the maximum throughput of wireless?

This FAQ isn't directly related to pfSense, rather it applies to wireless on all platforms, from anyvendor. Jim Thompson (netgate.com) posted the following (with some edits from me) to the list onDecember 2, 2005.

The overhead in wireless isn't limited to beaconing and CSMA/CA. The largest 'overhead' is that the802.11 MAC can't keep the air "full". There are delays due to turn around (for ACKs), overheadsdue to the preamble and headers, etc. 802.11g has a further requirement for "protecting" existing 802.11b clients by sending a CTS frame prior to sending the data frame (though this can bedisabled).

In theory (and I stress *theory*) the performance of 802.11's PHYs over TCP, with 1500 byte frames(802.11 allows larger frame sizes, but Ethernet does not) expressed in terms of maximum thoughputfor a single pair of stations (or a STA and an AP, if you prefer) looks like this:

802.11b: 5.6Mbps802.11a 27.3Mbps802.11g (no protection frames) 27.3 Mbps802.11g (with CTS protection frames) 13.0Mbps

And, you'll find that as you add users to an AP, the throughput does not fall-off linearly with eachnew associated station.

In theory the 'turbo' modes can get you 2X this, but sending twice the signal through the PA meansthat not only does tx power get pulled back, but the rx sensitivity drops, and the likelyhood of anerror sufficient to destroy the modulation envelope goes up as well. You will find that you can't get as many frames through (undamaged) running 'turbo' as you can with the same"standard" modulation rate.

802.11e offers an alternative MAC which can eliminate some of the 'dead spaces' in 802.11'sstandard DCF MAC. This can increase performance quite a bit. (And, in keeping this "on" the subject of pfSense, pfSense should be able to support thisnewer MAC, though I need to go see if there is a way to enable it.)

The Atheros chipsets also support compression of the datastream, and something called "fastframes" where the intra-frame protocol is changed to reduce overheads as well.

If you put it all together, and have near-perfect conditions, (and the moon is in the correct phase) apair of Atheros cards can stream data (say, a ton of zeros) back and forth around 90Mbps usingTCP. Cut the compression out and this falls to around 65Mbps. Cut turbo and this falls to around33Mbps. See above for throughputs without frame bursting and "fast frames".

Of course, at short range required to actually see 90Mbps, you might as well use an Ethernet cable.

The real news here is that, with a bit of work (say to add the 4-address frame support that madwificurrently enjoys) pfSense should be able to 'bridge' across wireless with 30Mbps or more at

URL: http://faq.pfsense.org/index.php?action=artikel&cat=12&id=112&artlang=en

http://faq.pfsense.org/index.php?action=artikel&cat=12&id=112&artlang=en