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Wireless Mesh Networking With The XO Laptop

Aaron Maxwell QA Engineer, SnapLogic, Inc. amax@redsymbol.net Bay Piggies Presentation 2008.01.10. Wireless Mesh Networking With The XO Laptop. Mesh Networks. Every mesh-enabled node acts as a relay to extend the wireless network range

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Wireless Mesh Networking With The XO Laptop

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  1. Aaron Maxwell QA Engineer, SnapLogic, Inc. amax@redsymbol.net Bay Piggies Presentation 2008.01.10 Wireless Mesh NetworkingWith The XO Laptop

  2. Mesh Networks • Every mesh-enabled node acts as a relay to extend the wireless network range • Meets many technical challenges for deploying in developing and rural environments • IEEE 802.11s – draft for mesh networking

  3. reduced throughput greater complexity of nodes (each is a router/transmitter)‏ security challenges Pro and Cons of using Mesh Network Architecture • Range extension • (potential) power efficiency • dynamically self-configuring/healing

  4. Networking Requirements • Extremely low power needs • Incrementally updateable (to improve functionality, standards adherence)‏ • Machines can act as mesh points even with main CPU powered off

  5. Networking Hardware • Marvel 88W8388 and 88W8015 (Libertas series)‏ • Regular 802.11b/g (2.4GHz) interface; mesh networking chip • Effort to eliminate dependency on closed-source code: http://dev.laptop.org/ticket/46

  6. 802.11s Mesh Architecture • Mesh Point (MP) – a device in the mesh network • Mesh Portal (MPP) – an MP that is connected to the external network • Mesh paths formed over inter-MP links using a routing protocol

  7. XO Mesh Protocol • Goal is to follow 802.11s as close as possible, but there are some compromises • routing protocol: simplified version of HWMP (Hybrid Wireless Mesh Protocol)‏ • Dynamic, Reactive

  8. Dynamic Path Selection • Mesh Points (MPs) will want to find (good!) paths to other mesh points • Custom routing protocol – mainly takes place at data link layer • Each laptop acts as an MP. Mesh links established via an RREQ/RREP cycle

  9. RREQ/RREP Cycle (Path Discovery)‏ • broadcast route request (RREQ)‏ • propagating nodes receiving RREQs create “reverse routes” in their routing tables • When RREQ reaches destination node, unicast route reply (RREP) is sent back to source • Nodes propagating RREP record “forward routes”

  10. External IP Subnets Image Credit: cozybit OLPC Mesh white paper

  11. Mesh Portal Association • MPs (mesh points) must find a path to an MPP (mesh portal) to access the internet • For power efficiency and maximum throughput, need to select “close” MPP • Builds on RREQ/RREP cycle • Clever solution...

  12. Mesh Portal Selection • RREQ sent to ANY_MPP_MAC_ADDRESS, a special anycast address claimed by all MPPs • Path selection algorithm gives higher precendence to lower cost routes • Current metric: link cost based on transmission power needed to send a data frame

  13. More info • Slides and links: http://redsymbol.net/talks/ • “Wireless Networking in the Developing World”: http://wndw.net/ • Cozybit (Javier Cardona): http://www.cozybit.com/whitepapers/olpc-mesh.pdf • Or email me at amax@redsymbol.net, or post on the bay-piggies email list (http://baypiggies.net)‏

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