On 08/24/2010 12:11 PM, L. Aaron Kaplan wrote: >>>> The largest of our mesh problems did not have to do with >>>> scalability on sheer number of nodes but rather scalability in >>>> density. Is there any information available on how these networks >>>> perform when there are 50 - 100 of them next all in the same room >>>> or in adjacent rooms? >>> >>> Yes! And the answer is very very simple: turn down the txpower! >>> ;-))) >> >> Can you provide me with a pointer to the numbers? Whats the maximum number >> of nodes can you have operated in a given area and what sort of network >> traffic tests did you run? >>
> Well, the community wireless networks are not very much about very dense > settings. We try to cover large areas with external (outdoor) antennas but > still have very many nodes in one single mesh covering a whole city or so. > See the attached current map of the Funkfeuer.at network. Yes. This is my point. Comparison of our scenarios to those scenarios is not really a valid comparison. > BUT!! Because we don't have a mesh with 100s of laptops in one room, does not > mean, we don't know physics ;-) > Since you asked if I know an example where there are many laptops in one room: > One example that I know that worked brilliantly well with many wireless > devices in one room was the RIPE meeting in Amsterdam. There they regularly > have many small APs below the desks in the meeting room and these are turned > down very much in "volume" (txpower). > The effect is that they only cover a small area ( remember, power decreases > by the square of the distance). > So this is a way to avoid a lot of noise of many laptops in a small room. Yes. I'm not disagreeing with any of the above. I'm just asserting that OLPC has limited development resources. Before we try to allocate any of these resources on a mesh implementation there needs to be _clear_ indication that the said mesh implementation can work in place of APs in a RF dense environment. Not necessarily better than APs because not having to purchase/manage the APs is a win but if its worse then the decision metric becomes less clear. > Another feature that you IMHO should look at is 802.11n devices (and of > course also turn down the "volume" there!). These offer higher bandwidths in > addition to actually using the multipath effects. > When you have many many laptops in one room and everybody "screams"/sends > very loud then you have lots of "echos" (multipath fading) bouncing off the > walls etc. 802.11n thrives off these multipath effects. We have and n is not an option for us yet and of course won't ever be an option for XO-1 unless they use some sort of external adapter. 1.5 has a replaceable wlan adapter but someone would have to produce a SDIO module for it first. -- Richard A. Smith <rich...@laptop.org> One Laptop per Child _______________________________________________ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
