Wireless
Design Goals
OLPC's laptops will be deployed in places where there will be very little or no infrastructure at all. We wanted to make sure that the laptops could connect to other laptops in their vicinity regardless of the presence or not of connectivity infrastructure. We also wanted to help kids share Internet connectivity without any additional infrastructure.
It became very clear that the utility of the usual laptop wired connectivity options (ethernet, modem) will be very limited under those constraints and a relative waste of our limited bill of materials budget. Instead we have to concentrate our resources to increase the utility and functionality of the wireless network adapter.
To achieve our design goals we chose to add self organizing multihop (mesh) networking capabilities to the laptop's network adapter. The constraints imposed by our Mesh Network Details mandate the use of System on Chip (SoC) Wireless Adapter, with the mesh networking protocol running directly on the adapter's CPU.
Network Adapter
- Marvell 88W8388
- Has onboard ARM 9 processor, ROM and RAM.
- 802.11b/g radio
- Dual adjustable, rotating diversity antennas ("Bunny Ears")
- Further details on the chip can be learned by reading Marvell adds TCP/IP offload support to WLAN chip
Installing Wireless
Tested with Build 76 by Quozl and JvC on OLPC hardware. Verified it still works on Build 81 by Scytacki. rminnich just tested and build 83 works. Teus confirms that build 91 works.
- Attach antennae (so as to prevent damage)
- Obtain the firmware file usb8388_A1_W8015FP14_FW2.bin from https://www.marvell.com/drivers/driverDisplay.do?dId=160&pId=38
- Rename the file to /lib/firmware/usb8388.bin
- Reboot
On builds later than 153 the firmware is already in the image. With build 179 and later NetworkManager with WEP should be working. In those builds all you need to do is click on the wireless strength icon on the upper right hand corner and select your network from the drop down menu. If the device is protected with a WEP key you will be asked to enter it. Subsequent boots of the device should automatically find and associate to the networks it has used before.
The result was that eth0 appeared in ifconfig, and the browser was able to access google.com, thanks to the automatic network configuration.
If you need to setup specific Essids or Keys, look at /etc/sysconfig/network-scripts/ifup-wireless for documentation, and add appropriate variables to ifcfg-eth0
If the security properties of an access point change, NetworkManager may be unable to access it. In that case you can remove or edit /home/olpc/.sugar/default/nm/networks.cfg
Mesh wireless
The Mesh wireless protocol it's an implementation of the 802.11s draft.
User Experience
There is quite a bit of complexity to propoerly configuring the wireless network in the variety of use scenarios that the children will be encountering. Our bias is towards making efficient use of mesh networking, but in some situations, infrastructure mode will be used. In those cases, the laptop will offer mesh portal (MPP) services to other laptops in the vicinity. If no mesh or access point is visible, then the laptop will become a mesh point on Channel 1. An additional bias to our approach is to use Channels 1, 11, and 6 when possible. This is an efficient use of spectrum as it lets us use three channels with essnetial no overlap.
The basic flow:
- Start with Channel 1
- Try DHCP
- If successful, then CONNECTED/DONE (DHCP)
- Try AUTOID
- If successful, then CONNECTED/DONE (AUTOID)
- Goto Channel 11
- Try DHCP
- If successful, then CONNECTED/DONE (DHCP)
- Try AUTOID
- If successful, then CONNECTED/DONE (AUTOID)
- Goto Channel 6
- Try DHCP
- If successful, then CONNECTED/DONE (DHCP)
- Try AUTOID
- If successful, then CONNECTED/DONE (AUTOID)
- Try last successful AP
- If successful, then CONNECTED; offer MPP/DONE.
- REPEAT DHCP/AUTOID loop on all channels.
- No connection? Become Mesh Point on Channel 1.
Rollover should reveal the difference between DHCP and AUTOID; IP address, Gateway, DNS. AP or Mesh, ESSID, Channel#. Signal Strength (AP only).
AP icon on Mesh View should distinguish between access points that are open vs. requiring a key. AP icon on Mesh View should distinguish between access points on channels 1,11,6 and other channels. AP icon should indicate that you are offering MPP service to others. Ethernet icon should indicate you are offering MPP service to others.
From the Mesh View, you should be able to jump directly into Steps 1, 16, or 19.
