On https://docs.google.com/document/d/1o6QtzLb6e58YKWqMf_junux2XyBRLFm31un8YLcYslg
Anna, Ben, Jon, Martin, Adam, Tim, TK, and Tom wrote: > Very confounding Wifi: while connecting initially, large numbers of > XO-1s fail to (re?)associate with Village Telco / Mesh Potato and > other AP’s. Even while larger numbers of XO-1s connect very > successfully to TP-Link 3020 AP; and can see Android phone AP’s. > 802.11s mesh networking cannot be the only root cause, but might > turning off mesh and/or setting the channel to 9 mitigate the worst > problems? You would need to test at least ten TP-Link 3020 APs before you could reliably claim that XO-1s connect very successfully, because of the manufacturing variances in the APs. The behaviour described sounds like a normal response to a dense networking environment. After my investigation yesterday, and reproducing with a group of six XO-1, I can give you some advice. When designing a classroom network, the XO-1 has a special feature to consider. The XO-1 will consume more of the available bandwidth than an XO-1.5 or later, because each XO-1 continually transmits mesh beacons even if mesh is not in use. Each XO-1 also responds to every scan (probe request) by every other laptop. As the number of laptops in a classroom grows, the available bandwidth will be depleted much sooner with an XO-1 than with an XO-1.5 or later. How to deal with it in the field? Make a scoring system for each channel, 1, 6, and 11. Give each classroom AP on a channel a score of 12. Scan, and give each AP outside the classroom on the same channel a score of 12. Give each XO-1 a score of 4. Give each other device, such as XO-1.5, XO-1.75, or XO-4, desktop computers with wireless, other laptops with wireless, tablet computers, Android phones, and iOS phones, a score of 1. Work to minimise the score. Here's some examples: 1. A group of 10 XO-1.5 and one AP will have a score of 22, 2. A group of 30 XO-1.5 and one AP will have a score of 42, 3. A group of 10 XO-1 and one AP will have a score of 52, 4. A group of 30 XO-1 and one AP will have a score of 132. 5. A group of 30 XO-1, two tablets, two mobile phones, two APs, two APs next door, will have a score of 172. -- Technical details: "Give each AP on a channel a score of 12." An AP transmits a beacon every tenth of a second (102.4ms), and responds to every probe request sent. "Give each XO-1 a score of 4." An XO-1 transmits a beacon every four tenths of a second (409.6ms), responds to every probe request, and transmits probe requests every 30 seconds for scanning. "Give each other device a score of 1." Each other device will transmit probe requests for scanning. Verification: Configure a nearby Linux system to act as a wireless monitor, for example; ifconfig mlan0 down iwconfig mlan0 mode monitor ifconfig mlan0 up tcpdump -i mlan0 -s 0 -w mlan0.tpcdump (^C after a minute) wireshark mlan0.tcpdump Measure the transmission rates for beacons and probe requests. -- James Cameron http://quozl.linux.org.au/ _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
