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Wireless Mesh Networking

NOTE: This talk item was moved from Talk:Hardware specification


sorry, just a question of an interested reader:

with the problem of lack of communication infrastructure in these countries olpc seems appealing to me to use as a filler: i envision the use of a lot of these devices to build a mesh...

(so my question: what is the range of connection free-to-air (outside buildings) to have an idea whether this is feasible..., thanks, thomas

(woot, first time using discussion!)

So that is one of the big question, wireless range. The true testing of signal efficiency is going to be tested this month with the first batch of test machines getting produced. With the antennae up (bunny ears on either side of monitor) the area of signal is greatly increased. Combine that with the lower bandwidth setting (2 or 4 Mbps, rather than trying for 54) increases the distance the signal will reliably travel signfnicantly. My guess is something like 500+ feet line of site. What the actual specs and capabilities are will be something that we will find through testing soon. Hope that heps, mburns

Hi, I am adding some more informations about the $100-Laptop in the german wikipedia (link: I would like to get to know what long way can be two laptops away from each other

  1. in a building
  2. under perfect conditions outside a building.

If someone gives me reply I will insert it in the german wikipedia. User: Betbuster 08:50, 19 December 2006 (EST)

The Ask a Question section states that "In excellent conditions, [range is] over 1.3 km. (along a rural road, held up high)" Are there more details on practical range, and what constitutes excellent conditions? Dialectric 19:59, 26 November 2007 (EST)

Chip selection

Apparently the Marvell 88w8388 WLAN chip (with advanced 802.11 a/b/g RF transceiver) was selected at least partly for its inherently low-power operation. The 88w8388 includes a built-in ARM CPU and a "thick MAC" stack, giving it the ability to relieve the AMD Geode host CPU of TCP/IP stack-handling chores. Consequently, the 88w8388 also has the ability to forward packets (e.g., within in the WLAN mesh) even when the host CPU is in the S3/off state, resulting in considerable power savings over conventional WLAN chips (like the Atheros chip considered previously). This is old news.

Newer news, however, is that a later chip, the Marvell 88W8686, maintains these capabilities with even less power consumption (under 400 mW) and smaller footprint (50 square mm), at least partly because it is implemented at 90nm instead of 0.15 microns. Marvell's press release about this came out on 7-20-2005 (

Since Marvell is a member of OLPC, presumably the OLPC team is aware of the newer, lower-powered chip. Nonetheless, this OLPC website still seems to reflect only the 88w8388 in its discussion. Because of the project's emphasis on low-power operation and cost reduction, it would seem appropriate to at least have some discussion of two chips' respective merits, relative to the project. Although it's likely that the 88W8686 arrived too late to be incorporated into the first-generation, perhaps it would be appropriate for the second, unless some other factor(s) like cost or availability rule it out. It would be interesting to get authoritive input on this aspect.

It would also be good for an OLPC team member to weigh in on whether 802.11a mode will also be supported in addition to 802.11b/g, since this capability is inherent in both chips mentioned here.

Sausage making requires the right volume of components available at the right time. - jg

Multicasting issues

Mesh networking is cool because it creates a spontaneous network, including one that can span vast distances compared to a conventional WiFi hotspot established with a single WAP. But I am curious how one manages things when nodes get very dense, e.g. in a classroom where every node might be directly connectable to every other one. Surely there is no harm in enjoying the reliability of highly redundant alternative paths given unicast traffic. But does anything unfortunate happen when you want to support multicast traffic?

I assert multicast is important for a classroom setting where we want each child's laptop screen to replace the pre-cybernetic method of sharing a common image - the blackboard/whiteboard. (Note this modern method obviates the delay of walking to and from the board!)

My knowledge of WiFi multicast is limited to the tutorial: in which one begins a multicast session by sending unicast dataframes to an access point. Within the mesh networking scheme planned, will any laptop then act as a suitable access point for such a multicasting methodology? Or are there complications I don't understand and which have not been addressed?

The cited tutorial also warns of the hazard of having a single "spoiler" client in power-savings mode when one is multicasting. Is this issue also germane here?

If multicasting will be supported, what means might be available to prevent its abuse by naughty kids? When I was a child many decades ago, my classmates would sometimes design at disrupting the classroom decorum by passing packets (using paper for OSI Layer One!) Will securing the teacher's supremacy of the airwaves be a matter for the software to address? Or should only a special "teacher" laptop be able to multicast packets?

Perhaps you might chastise me for not posting this discussion to the Software_specification, but the data link layer is very alien to nearly all programmers!

- Docdtv 01:33, 25 October 2006 (EDT)

Since I wrote the stuff above, we've been advised that OLPC is opening the kimono with regard to the Sugar-XO User Interface (UI). Reviewing the UI docs starting to appear in this Wiki makes it manifest that the mesh nework is deeply integrated - not a mere afterthought for apps to exploit.

We all know the phrase "It's not a laptop project; it's an education project." But do I now hear someone in the back of the room saying "It's not an education project; it's a groupware project." ? <G>

Anyway, the "blackboard replacement" question about which I pondered aloud above is addressed by the (multiple) "bulletin boards" - one for each of the various levels of pseudo-geographical zoom - as well as for each of the separate live "activities".

Since these features are a matter of software, I'll write no more about them here. But my curiosity about the multicasting efficiency issue remains. It's just that now it is obviously all the more vital.

- Docdtv 03:59, 2 December 2006 (EST)

Apropos of this discussion, item 4 in the 2006-12-09 OLPC News looks to the fallout from breaking the symmetry of all the nodes in a mesh by introducing "server" nodes: the mesh protocol is subject to change. Note that the Libya project includes servers.

- Docdtv 01:58, 14 December 2006 (EST)

The server as a node on the mesh has been part of the plan from day one. It is not driven by any special need in Libya. There will hopefully be other devices in the mesh as well, e.g., a projector, perhaps the occasional printer, etc. --Walter 16:02, 14 December 2006 (EST)

Doc; The following might be interesting as a description for messing with someone's packets and preventing said mess can be as instructive as a ton of dry specs. Go down to man-in-the-middle here. or
Surpressing attacks. After establishing the structure of the mesh, redundant packets are broken up and sent by alternate routes to the destination machine which checks for integrity and identifies problem nodes. So the mesh is a lot safer than a straight line hand-off. For a discussion and display of constructivist education you should go to Moodle which I have used for nearly five years with great success. You can see that it is in thousands of schools world-wide so the disingenuous "concern" of critics over the poor state of education in other countries is often a trick of misdirection. As in "evolution is only a theory."

Bob calder 20:00, 2 December 2006 (EST)

Wireless mesh-network standards?

Where can I learn about the standards that will be used for the wireless mesh network? As far as I know, there is not yet a widely accepted standard for wide-area mesh networking, but I was hoping I might find some ideas here.?

IEEE 802.11s is under development. Unfortunatly, IEEE's process is not transparent to the degree the IETF, and so you can't just download the standard-under-development. - jg

MAC Address

is OLPC registered at the IEEE with its own manufacturer part (Organizationally Unique Identifier)?

What MAC uses the B1 demohardware?

88w8388 and mesh networking in other platforms?

I'd like to know if it's possible to buy a 88w8388 and attach it to a computer running Ubuntu (for example) and benefit from the mesh networking capabilities. Will the driver compile in other platforms? What about the firmware? I'm using for mesh networking but OLPC's mesh seems a very good alternative.

Fragility of the ears

My experience with toys and kids (my own kids -- you cannot believe how many toys I fixed) and an attempt to design a teaching doll indicates that anything that can break will break, and the more moveable it is the more likely it will be broken. The ears look like handles and probably will be used as such. Stuff will be poured into the machine, scratches will appear on the screen (I scratched the LCD screen of my new PowerShot A570 IS after only 1 week of use -- I put it in my pocket), the keyboard will be pounded on by baby brother, etc.

Drop tests: I've had a lot of experience with drop tests: the machine should be able to survive at least e.g. 3 random kid-high drops (e.g. 3 feet) onto concrete (not a wooden floor or hardpack dirt) with full operational capability after the tests (do on a sequence of samples).

Rollover tests: Where I used to work (plasma-arc metal cutting equipment) we did 50 rollovers (from the CG) side to side in both directions, again with full operational capability after the test. This may not sound like much but at filrst the results were devastating and replicated HALT and HASS tests in chambers especially with regards to whether or not screws would back out, capacitors and chips and resistors would pop off boards, etc.

I was a proponent of the cruelest of all tests: we put all the tests in series and tested for operation after each test. Three machines had to survive the abuse. wvbailey, 17:59, 23 July 2007 (EDT)

This comment was moved into the discussion, and is now addressed in the main section. The drop tests to which test laptops were subjected to are worse than described here.--Wad 01:24, 10 November 2007 (EST)

Tcpdump RPM

Wi-Fi Compatibility

The XO does not appear to be compatible with 802.1X/WPA2, which is widely used on campuses in the US. While this may not be a problem in the targeted markets, it could hinder development of new applications.

Kids probably doesn't need that yet. But I would like to know if that's a limitation of hardware, or just merely the fact that SUGAR doesn't support it yet? Could I get 802.1X done with command line? 14:30, 21 December 2008 (UTC)

User Experience

The Wireless#User Experience section of the page is most likely out of date. I hobbled it together last summer. Could someone more familiar with the current expectations update this section? --Walter 10:14, 26 January 2008 (EST)