SDCXTRA RADIO

Thursday, March 19, 2009

Coaltion of Wireless Developers Part Five

About CUWiN

What Does CUWiN Do? | Meet the Team | CUWiN Press

CUWiN (the Champaign-Urbana Community Wireless Network) is a world-renowned coalition of wireless developers and community volunteers committed to providing low-cost, do-it-yourself, community-controlled alternatives to contemporary broadband models. CUWiN is fiscally sponsored by the Urbana-Champaign Independent Media Center, a non-profit 501c3.

Our mission is to develop decentralized, community-owned networks that foster democratic cultures and local content. Through advocacy and through our commitment to open source technology, we support organic networks that grow to meet the needs of their community.

To achieve that mission CUWiN maintains international and domestic partnerships with dozens of research institutions, not-for-profit organizations, community groups, businesses, universities, and government institutions. To inquire about becoming a CUWiN partner, send an email to cu-wireless-support@cuwireless.net.

More about CUWiN's vision can be found in this Vision Statement or by downloading a CUWiN brochure.

What does CUWiN do?

Software Development: CUWiN develops free open source, open architecture software for mesh wireless networking. CUWiNware is our flagship software. It utilizes wireless mesh protocols that we developed along with standard networking protocols and open source protocols from other projects. For more information, see the research and development page.

Wireless Consulting: CUWiN provides expertise in developing and maintaining wireless networks for your business, community, and municipality. We are currently involved with community networks in Chicago and Washington, D.C., as well as municipal networks in Urbana, Illinois, the Mesa Grande Reservation in Southern California, and Apirede, Ghana.

Community Education Programming: CUWiN provides educational programs about community wireless technology and telecommunications policy. Educational Programs are available to anyone, including policymakers, community organizations, and educational institutions. For more general purposes, CUWiN hosts Hack Night the last Sunday of each month at 5 pm in our office space at the old Urbana Post Office. Hack Night is an event for people of every technological ability, as activities range from just gathering information to writing code for the project and experimenting with wireless hardware. Hack Night is free and open to the public.

Meet the Team!

Our staff page is a convenient resource for identifying who is working at CUWiN headquarters. By no means is this an exhaustive list, nor does this represent our extensive team of developers who are working on the software. A more extensive list is available on contact page.

Press Coverage and Press Releases

Our press page is designed to showcase the media coverage we've received and to provide media organizations a place where they can easily access the latest CUWiN press releases and media alerts. Expect the list to grow as more people and organizations discover CUWiN and track its progress.

CUWiN Press Coverage

Press Coverage

Web and Print

Radio

Press Releases

CUWiN Releases CUWiNware 0.7.0, 19 September 2006

CUWIN Manual

Preface: Building Your CUWiNware Wireless Network

This manual will walk you through all the decisions that need to be made when purchasing and building hardware for a CUWiNware network.

First, a few definitions. CUWiNware (pronounced "Q-N-Ware") is the wireless server software created by the Champaign-Urbana Community Wireless Network project. A CUWiNware network is simply a mesh of access points, or nodes, running the CUWiNware software. A node consists of a computer, a wireless network card (NIC), an enclosure, an antenna, and all the neccessary cable and mounting equipment. Because these nodes can be built using any brand of computer and hardware store parts, you are not bound to any one hardware manufacturer, giving you the flexibility to build the ideal network for your situation.

Many of the decisions that you will make will be based on the local circumstances of your community. Topology, budget, available labor, available materials, network type, and network size will all need to be factored into your network design.

Index

Hardware Design and Construction

Introduction

A CUWiNware network is a mesh of nodes running the CUWiNware software. A node consists of a computer, a wireless NIC, an enclosure, an antenna, and all the necessary cable and mounting equipment. This manual will walk you through all the decisions that need to be made when purchasing and building hardware for a CUWiNware network.

Many of the decisions that you will make will be based on the local circumstances of your community. Topology, budget, available labor, available materials, network type, and network size will all be factors that go into your decisions. One of the biggest tradeoffs is between time and money -- for each option there is generally a way to do it cheaply that takes a lot of time and a way to do it quickly that is more expensive.

Node Placement

Where a node is located can make or break the quality of its connection to the mesh. Ideally, antennas will have a line-of-sight to each other in order to get the best reception. In order to minimize signal degradation, the cabling between the antenna and the wireless receiver card should be as short as possible. This often means that you need to put both the antenna and the rest of the node above as many buildings and trees as possible. On the roof tends to be the standard node placement location.

Isolated Areas

Areas that are isolated from the local mesh can often get a signal from the main mesh by using a well placed directional antenna instead of an omnidirectional antenna. Such isolated areas can then use an omnidirectional antenna to share the connection with neighbors. In this manner, areas that were out of reach to the mesh can become connected satellite meshes. When the mesh extends itself in the future to encompass the satellite, both meshes will merge seamlessly with each-other.

Rural, suburb, and other fringe areas often find themselves without any broadband service provider. These communities can find a donor business or home in a nearby community that has broadband and is willing to share by setting up an Internet gateway node. Once a link is established with the distant community, the mesh can be spread wirelessly among the members of the community that was once isolated. In this manner, communities can equip themselves with both broadband and a municipal network.

Using consumer grade equipment, links of over 50 miles (80.4 km) have been established. See the antenna guide for more information on antennas.

Coverage Requirements

A common question that immediately pops into the minds of people planning a wireless mesh is "How many nodes will be required to cover our area?" Unfortunately, this is one of the hardest to answer because of the variety of aspects involved.

The amount of radio activity in your area is one influential factor. Sources of radio interference can be as powerful as the government and various utility companies. Sources of interference can also be as mundane as a cordless phone or the microwave oven. A wireless signal may be strong in an area, until someone picks up the phone and the reception drops to zero.

The terrain of an area also strongly affects the quality of a signal. Even a few feet of soil will block a signal entirely, so a node that is in a valley will have much worse reception than a node on a hill. If there is a hill between a node and the rest of the mesh, a second node may be needed to route the signal over or around the hill. Similarly, a node that is located at the top of a hill may be able to establish a weak link to very distant nodes. Distance records for longest link are often set by using directional antennas on mountaintops.

Foliage such as trees also play an important role in signal strength. The water in trees and the needles of some types of conifers are fairly effective at absorbing a wireless signal. It is not unheard of for a weak wireless link to be usable in the winter when the leaves are off of trees, but unusable in the summer. There is a similar problem with wet leaves (such as during a rain) blocking a signal.

Buildings will also block a signal as effectively as small hills. Brick, stone, and metal siding are the most opaque building materials, and may need to be routed around. It is far better to place a node on top of a tall building than beside it.

After all this, what would we say are normal coverage requirements? The twin cities of Champaign and Urbana in Illinois, where CUWiNware is being developed, are about as flat as cities get. We don't have particularly tall buildings here, but we have many tall trees, so we should be around average. Currently our longest link is around 400 meters. Of course, if you are planning a new network, it is best to put nodes closer to each-other than 400 meters, 100-200 meters is ideal (depending on the area, as discussed in previous paragraphs).

One of the CUWiNware developers did the calculations for how much a mesh would cost to cover one square mile at $350 per node. If you can reliably obtain one thousand foot links, you only need nine nodes at a total cost of $3150. If you can only obtain two hundred and fifty foot links, you will need one hundred and forty two nodes at a cost of $49700. It should be noted, though, that a long term goal of CUWiN is to run on hardware that costs less than $100. That would move the cost of the setup with two hundred and fifty foot links down to $14200.

Supported Chipsets

One of the most important choices you face when building a CUWiNware node is what wireless NIC to buy. Wireless NICs use a variety of chipsets depending on the the manufacturer that makes them. The chipset that your wireless NIC uses must have drivers in NetBSD that support Ad-Hoc mode.

Theoretically different chipsets can be used in different nodes on a CUWiNware network as long as they are supported by NetBSD but because of various bugs/quirks in the firmwares of various chipsets, it is often best to standardize on a single supported chipset for all the nodes in your network.

Chipsets

    • Intersil Prism - The prism (version 2, 2.5, or 3) chipset is used in some PCMCIA and PCI cards manufactured by D-Link, Proxim, SMC, and others. This chipset is well supported in Ad-Hoc mode with no real bells and whistles. This may be the best chipset available if low cost PCI cards are needed for low-resource nodes.
    • Atheros - Atheros makes the most advanced 802.11x NICs currently available. This is the chipset currently recommended by the CUWiN team. Most tri-mode a/b/g cards on the market use the Atheros chipset. The Atheros chipset features a Hardware Abstraction Layer which puts most of what would traditionally be in the firmware into software. This means that when/if the interface to the cards is fully opened up to programmers, arbitrary control of power levels and other low level features will be possible. Because future versions of CUWiNware will take advantage of this fine grained control we recommend investing in cards with this chipset now. Atheros cards may be a bit more expensive than some of their competitors and the drivers for the Atheros cards are not as mature as those for the Prism cards so there may be bugs, but these drivers are being actively developed and debugged by the CUWiN team.
    • Hermes - Most cards made by Orinoco, Lucent, WaveLAN, and Proxim use the Hermes chipset. These cards have very good sensitivity with low power radios and they are supported in NetBSD but they suffer from serious firmware problems relating to their IBSS ids. The IBSS id needs to be the same throughout the mesh but cards with this chipset often "split" the IBSS in a way that can only be fixed by rebooting all nodes on the network in a certain order. This chipset should generally be avoided for any Ad-Hoc network as just one Hermes chipset mixed in with other nodes can cause a serious network split. Firmware upgrades do not appear to completely solve this problem. Aironet/Cisco chipsets have the same problem.
    • Other Chipsets - Development of drivers for new chipsets is constantly in progress. Some manufacturers publish the specs for their hardware which makes driver development fairly straightforward. Other manufacturers keep their specifications proprietary which means that NetBSD developers have to reverse engineer the interfaces. Support for the ADMTek ADM8211A is available now and support for other ADMTek chipsets such as ADMtek ADM8211C/CR is expected soon. Support for the Realtek RTL8180 chipset has also been added.

Links

Constructing a Rugged Outdoor Node

One of the biggest sources of signal loss in a wireless network is in the cable between the low power radio in each node and the antenna. High quality antenna cable is very expensive. In order to maximize signal strength and to minimize cost, it is best to put the node as close to its antenna as possible. This generally means putting the node outdoors on the rooftop on the the same mounting pole as the node itself.

Outdoor nodes need to have no moving parts, withstand extreme temperatures, withstand rain, snow, wind, sand, and other local climate conditions and be upgradable without physical access.

Single Board Computer

The first component of any outdoor node is the single board computer. This is a small form factor motherboard built for embedded computing applications. Typically a single board computer will be built to industrial standards and will be much more rugged than a typical consumer motherboard.

Typically a single board computer will have a processor (CPU), some memory, some compact flash storage (or a slot for it), one or two Mini-PCI or PCMCIA slots, one or more ethernet jacks, a serial port, and an input for DC power.

In order to run current versions of CUWiNware you will need a single board computer with an x86 CPU, preferably 486 or better running at 100 MHz or better. It will need at least 64MB of RAM and 64MB of compact flash.

The 64MB of compact flash is necessary to contain two full versions of the software which is currently around 32MB in size. The space for the second image is used for on-line upgrades of the node. It may be possible to build custom versions of CUWiNware with on-line upgrades disabled that would only require 32MB of compact flash.

Make sure there is an enclosure available for the board you choose!

We recommend Soekris Engineering's net4526 board which has 1 ethernet interface, 2 Mini-PCI slots, 64MB of on-board compact flash, and 64MB of on-board RAM. This board is small, powerful, rugged, and has good enclosures available.

As I write this (August 2005) a complete, quality, node can be bought for around $300, but it is the eventual goal of the CUWiN project to run on hardware that costs less than $100.

Links

The Wireless NIC

The three requirements for a wireless NIC are that it must have an external antenna connector, it must be compatible with the motherboard you have chosen, and it must use a chipset that is compatible with NetBSD in Ad-Hoc mode.

Interfaces between the motherboard and the wireless NIC include: Mini-PCI, PCI, PCMCIA (a.k.a. Cardbus or PC Card), and USB. Most rugged single board computers will use either PCMCIA or Mini-PCI cards.

Make sure there is a pigtail available for the card you choose!

We recommend Netgate's NL-3054MP Aries Mini-PCI 802.11b/g or SL-5354MP Mini-PCI 802.11a/b/g cards. These use the Atheros Chipset.

Links

The Enclosure

The enclosure you choose must allow your single board computer to be mounted. Many enclosures come with a special mounting plate that the manufacturer can custom drill to work with any single board computer that you specify. Many manufacturers make enclosures specifically for Soekris boards. The enclosure must have holes for an ethernet cable gland and and an N connector for the antenna connection.

Any enclosure for an outdoor wireless node should be rated at least NEMA Type 4x. Type 4X NEMA enclosures protect against falling dirt, rain, snow, blown dust/sand, splashing water, and ice.

The enclosure should be white in order to reflect rather than absorb external heat from sunlight. If the enclosure is plastic, it must be a type of plastic that doesn't break down when exposed to UV light.

It is vitally important that any and all holes on the enclosure be on the side that faces downwards. No matter how well sealed the hole, with mastic tape or with a cable gland and gasket, if it is on top water will pool around it and freezing/thawing will allow the water to seep in. After months or years of operation the node will fill with water and fail.

It is best not to mount the antenna directly onto the enclosure but to mount both the enclosure and the antenna on a mast. Antennas directly mounted on the enclosure put a huge amount of stress on the joint between the antenna and the enclosure and this can cause leaks.

There is some debate among community networkers as to the utility of a drain hole in the bottom of your node enclosure. If you trust that your node will remain absolutely water tight even after months or years of freezing and thawing then it may be best to not include a drain hole. A drain hole is for water that does get into the enclosure due to condensation/humidity or due to leaks. A desiccant package placed in a sealed node may do a better job of defeating small amounts of moisture. A drain hole may be susceptible to sand or dust in a desert environment and would definitely not be recommended in that case.

A very labor intensive but low material cost way to build an enclosure is to use a surplus military ammunition can painted white with a custom plexiglas mounting assembly. These cans are built to be very rugged and waterproof and are essentially free if you can find a source of them. They do, however, corrode after prolonged exposure to the elements and will eventually fail.

We recommend the NEMA-4x enclosures sold by Metrix Communications for use with Soekris 4526 boards.

Links

Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)