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sf.desc
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Cloud Hub: Yet another implementation of wireless mesh networks
Introduction
This is an implementation of wireless mesh networks. It is intended
to be a firmware upgrade for inexpensive wireless routers such as the
Linksys WRT54G. The idea is to make it easy to build up wireless coverage
throughout large homes, office buildings, and multiple-building campuses
by setting up inexpensive routers that will configure themselves into
optimal wireless meshes. Clients can then gain access to the internet
either by attaching cat-5 cable to one of the boxes, or by joining
the mesh as an "ad-hoc leaf node" which requires no special software
or drivers.
Here is a summary of the key features of this implementation:
It is a link-level implementation, meant to be thought of as a single
large "ethernet hub".
From the user's perspective, a hub is a simple device: plug it in,
and then attach cat-5 cables to it.
The goal of the cloud hub project is to make a wireless mesh close to
this level of simplicity.
Get a new wireless box, install the cloud hub firmware, plug it in, and
it finds your other cloud hub boxes by itself. Connect your computer to
it with a cat-5 cable, or set your computer's wifi card to ad-hoc mode,
and you're done. (Well, almost. If you want, you can access a simple
internal configuration web page and set wifi parameters such as SSID
and WEP to your preferences.)
Configuration, to the extent that it is necessary, is uncluttered
and simple.
The wireless routers continuously sense wireless signal strength.
They update their connectivity among themselves automatically to optimize
overall signal quality.
In addition to wireless connections, the cloud hub boxes sense each
other via cat-5 connections. So, if you have more than one cloud hub
box that happens to be attached to your LAN, those boxes will find each
other that way and integrate with each other via the cat-5 connection.
The cloud hub software uses wifi ad-hoc mode. It permits standard
unmodified ad-hoc devices to integrate into the mesh as leaf nodes.
In other words, you can use a wifi-equipped laptop computer or beige box
with a wifi card in it. After configuring such a device into ad-hoc
mode, it will be integrated into the wireless mesh and gain access to
the network.
Ad hoc clients can roam throughout the mesh, and are dynamically handed
off to the nearest, best-signal cloud box.
The cloud boxes create a spanning tree of connections among themselves,
but make an effort to communicate parsimoniously to reduce wireless
traffic. Additional non-local arcs are added to the graph in those cases
where signal quality permits it. Each node has the responsibility to make
sure that its spanning-tree neighbors have messages propagated to them,
but if a node can construct a proof that its neighbor has the message
(having overheard it from some other box in the cloud), it will refrain
from redundantly transmitting it.
The internal web server has a display that shows a continuously updated
picture of the topology of the entire cloud.
The web server has a display of the wireless environment of the entire
cloud. Each node monitors its immediate environment for other wifi
access points and activity. About once per minute it transmits this
information throughout the cloud. So, every cloud box can show the user
all of the wifi activity seen by every node throughout the cloud.
From the internal configuration web server of a single cloud box, it is
possible to update the wifi parameters of all of the boxes in the cloud.
(As a security check, this will only work for boxes that share the same
administrator password and current wifi parameters.)
Security is currently 64-bit or 128-bit WEP.
The lights on the front of the WRT54G blink so as to provide a handy
picture of mesh status. They blink out the number of boxes currently
in the cloud, and how many boxes can be seen directly from each node.
In sum, the cloud hub project embodies few novel ideas for mesh networking
combined with attention to detail to create reliable, easy-to-deploy
wireless infrastructure.