Networking

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Mesh networking, &c. See also : Radio and broadcast

Network connectivity and mesh functionality was being headed by Michail Bletsas, Chief Connectivity Officer of the One Laptop Per Child organization.

Hardware

The laptop comes with a built-in wireless card compatible with 802.11b/g standards. Marvell developed the wireless chip and wrote its firmware and the initial device drivers. A unique ability of the laptop is that the wireless chip will have very low-level mesh routing capabilities built-in. Because of this, the laptop will be able to act as a router while the main processor is idle (turned off). In this mode, the machine is expected to use roughly 0.5 watts of battery power.

Two 'bunny ear' antenna on either side of the display swivel upwards. Doing this reveals USB and audio ports, normally sealed from the elements, and also extends the wireless range significantly to over 150 m and field tests even indicated ranges to 200 m.

Wikipedia's article on Ad hoc routing protocol notes that: "Transmitting a signal half the distance requires one fourth of the energy and if there is a node in the middle willing spend another fourth of its energy for the second half, data would be transmitted for half of the energy than through a direct transmission." Marvell's card is designed to scale to very low power usage. Lower power output allows for less wasted battery. Longer range transmissions are also possible with lower power/bandwidth, allowing a large area to be covered by the mesh.

An Active Antenna provides the same wireless mesh network interface in a USB peripheral. It may be used to connect a School server or other computer to the mesh network, simultaneously repeating any packets on the local mesh. It may also be provided with only power, in which case it acts solely as a repeater to extend the mesh.

Details on the card itself can be found on the wireless page.

Software

To encourage collaboration and to make maximum use of minimum resources, the laptop will implement 802.11s, a proposed wireless mesh standard from Intel intended for small home/office networks.

Additional details on the mesh networking are available.

The sources for the current community-developed driver for the Marvell 8388 are being hosted at infradead.org, discussions about its development can be found at the libertas-dev mailing list.

Deployment

Some features described on this page are a work in progress,
and might work as described only in some circumstances.
Please use the discussion page to make suggestions,
share how this works for you, and see other's comments.

OLPC is working with schools to saturate each location as they deploy machines. This solves several problems (jealousy, in-fighting, unequal opportunity to education) but also allows for optimal mesh conditions. Each school is working to have Internet access of some capacity, and school servers. The server will function as a gateway/proxy for many Internet services(web proxy, email server, ntp daemon), and as a beacon for Internet connectivity sharing.

The network itself is expected not to be more than 4-5 hops from any 2 nodes. Actual hop count, latency and bandwidth will require further field testing.

Press Coverage

• Audio Lecture - A public lecture in Greek by Michail Bletsas on the wireless mesh of the $100 laptop
• The Social Side of Mesh - Courtesy OLPC News

Ideas

• Have the laptops be able to intelligently turn themselves off when their routing abilities do not improve the network's mesh. In dense networks such as might be found in a classroom or apartment complex, having all idle machines function as routers may be inefficient for the overall network. This would further save battery on the machines, and simplify the network topology.
• Could simplistic packet shaping improve overall network throughput?