Seattle Wireless Network FAQ
This is the Seattle Wireless Network FAQ. You may find answers to questions you might have about our network. Also be sure to check out the ListOfDefinitions of our different type of nodes.
For questions about wireless networking technologies in general (i.e. questions that's not specific to our network), please consult the WirelessFrequentlyAskedQuestions.
- Seattle Wireless Network FAQ
- How Do I Get Started?
- Hardware Questions
Questions About Nodes
- Can I set up a link using a directional antenna pointed at an omni antenna
- Can I run a really long coax cable from my machine to an antenna on my roof?
- I want to build my own antenna. What is the best one for me to build?
- How the heck do I mount an antenna? I don't have any masts on my roof or anything...
- What protocols are we using?
- What radio band are we using?
- What hardware and software is required to connect to the network?
- Which IP ranges are used?
- What nodes are available for access?
- How does routing work?
- Will there be DNS services?
- How are clients authenticated to the network?
- How do I access the Internet?
- Can I roam?
- Can a 802.11 node be a repeater?
- What's with this 42 thing? I can't find an 802.42 spec or anything
- Any plans for 802.11a or 802.11g?
- How do I use the laptop in the car more conveniently?
- How safe is the microwave radiation from 802.11 devices?
- Why is the sky blue?
- What is the airspeed velocity of an unladen swallow?
Why would I want to participate in a Community Wireless Network?
- The point of our community wireless network (CWN) is to create a local network infrastructure that replaces the local loop that is, right now, owned by the telcos and other large corporations. Right now, we are in the development stage; just seeing if we can actually create a network using 802.11b. Once we get the technology developed to the point where it is easy for the lay person to set up we are expecting many more people to join in and start offering more services. A kind of "if you build it they will come" scenario. Many people will use it for gaming but there will be web, mail, file exchange, chat, server, etc. Any kind of service you find on the Internet you should be able to find on such a local network too. There will be people who set up gateways to the Internet and charge for access and there will be free ones as well. People will telecommute over it, people are working on voice over IP set ups for this type of network also. Most of this is a long way off but some of it is only a few months off. The network isn't competing with the Internet, it is working in conjunction with the Internet to supplement ways for you to better use connectivity.
As part of the network development process involving SWN members, we have a technical HackNight (check for current schedule). Not only do we have problem solving sessions, we share technical information and ideas about wireless and related topics through active participation.
Do you have regular meetings that I can go to?
We occasionally have meetings the second Sunday of the month, whenever there is something new to talk about, or if a special guest is in town. Check the EventCalendar for meeting dates and special event dates. At times, the meetings are also broadcast via streaming video at a URL provided to those signed up on the mailing list. Meetings have presentations, discussions on how something was implemented, face to face answers to questions, and have all the expected additional fun of meeting and talking with others for group projects or problem solving. You can also bring your 802.11b equipped laptop and connect to the net whilst at the meeting.
So will I be able to get free Internet access if I connect to SWN?
Some users (GatewayProvider's) do share their InterNet bandwidth over their nodes, but the goal of the Seattle Wireless Network (SWN) is not that of being an "ISP" to provide free InterNet access. The goal of SWN is to create a self-sufficient network that does not depend on the InterNet for content or connectivity. As for free InterNet access, it would be very easy for individuals to share their unused bandwidth with other users.
How do I connect to a SWN node?
- Just connect to a SWN node as you would any other node. Once connected, the node may redirect you to a splash screen web page description or menu of wireless community features available at that node. Among these features listed is typically access to the internet. Some nodes currently don't have splash screens and may put you on the net right away. The presence of splash screens is not new. For example, if you connect to a tmobile node at Starbucks, you will find your browser is redirected to a gateway webpage.
Some of the history can be observed by looking over the meeting agenda notes in the EventCalendar. Also, some of the oldest press coverage articles in the PressCoverage section may be informative. One foreign article was translated at LeMondeTranslation. Seattle Wireless does not charge dues for membership. The general meetings are open and free to the public.
How Do I Get Started?
I bought a WiFi client card, what do I do now to start using it?
Okay, you bought the stuff and now you want to use it. Assuming that you have followed its instructions for installation, and you are in range of a WiFi internet access point, your laptop/pc should be able to connect up to the internet simply by firing up your browser and trying to access a website. If this is not the case, read below and try things in the order presented.
First, set your SSID to that of the access point's network. Your card's software should provide you the ability to enter this string. You might not need to enter the string as an AccessPoint can broadcast an SSID that will be displayed if you use the scanning feature of your software to find the SSID. Example SSID include: the SeattleWireless SSID at the MeetingSpace is "seattlewireless" or "tmobile" if you are in range of a Starbucks coffee shop.
Second, the site you are connecting to should be using DHCP instead of Static IP addressing. If it is static, then the connection method is tedious and not covered here. Basically, the wireless access points that let you openly connect will be using DHCP. If static, your WiFi card will probably not connect to it and you should be able to see this via the driver/interface program that came with your WiFi card.
Typically, the driver software that came with your card will have a display indicator showing that it is in range of a wireless AccessPoint. Before you can connect to something, you will first need to be in range with a sufficient signal. If you are not in range, well, you need to create your own access point or find one in order to verify that you are able to form a connection.
If you are wondering what to do to use your first connection, well, fire up your browser and see if it connects through your WiFi card. Other internet clients can also be tried out (email, time synchronization, p2p, irc, etcetera). You can find some nodes to try at WhereToGetOn. One place that you can test is at your neighborhood Starbucks. Whilst it is a pay service, Starbucks has an access point to the internet; the initial webpage with the login prompt is free, so if you can display that initial webpage, you can prove to yourself that your gear is working. After all, if you can display the login page, then your wireless setup is definitely working.
The classic first error that may occur is that when you try to run the browser, it brings up the Dialup Modem requestor window instead of using the WiFi connection. If this occurs, your PC is looking for the dialup modem as the method for accessing the internet; thus your wireless card is ignored as a means of accessing the net. For your browser (assuming Internet Explorer), if you have been using a dial-up connection, you may check the browser properties to verify it is not set to "Always dial my default connection". It will probably be set to use dialup if you ever ran AOL or some local ISP client installer software that uses the phone line. Also check that the LAN Settings is "Automatically detect settings" and leave the Proxy server settings blank. If the above didn't fix your problem, you may need to check your network settings. For Network settings, find TCP/IP protocol for your wireless card and open its properties. On the properties, for IP Address, select "Obtain an IP address automatically". Also for DNS, select "Disable DNS" and for WINS, select "Use DHCP for WINS Resolution". You may need to shutdown and reboot to use the changes. Remember, if the shutdown is not successful, those registry changes might not have been saved properly and you might have to do it again. After a successful shutdown and reboot, bring up your browser and try to access a website.
If the above doesn't work, run the c:\windows\WINIPCFG.EXE program to see what PPP devices are available on your pc. You will see "PPP Adapter" in the menu selector box but there should also be an additional menu entry for your 802.11b wireless adapter as well. Look thru that menu. If the entry is not present, then the initial installation for the WiFi device was not successful (or you had a crash that forced use of an older registry). You should remove the WiFi card, and remove the entry for 802.11b in the Network settings property page. Shutdown. If you have a PC, install the WiFi card and reboot. If a laptop, simply reboot and after it is booted, insert the pcmcia card. You should see that familiar windows message saying that new 802.11 hardware was detected and installation is taking place. After this, run WINPCFG to see if there is now an entry for the 801.11b wireless adapter. Now fire up that browser and see if you now have wireless internet.... If it still doesn't work for you, and you are a SeattleWireless member, run into me at a group meeting and I will try to answer your question ( StartideRising ). Note #1: If you are able to get online, but after you reboot, it no longer works, simply go in to the Network properties and delete that first entry for the 801.11b wireless adapter. After rebooting, insert the pcmcia card and it will install once again. This type of kludgey work around is often used by Windows users who have messed up drivers/registry entries. Note #2: If the wireless card doesn't seem to connect, eject the card and re-insert the card. It is recommended that you first turn off power to the card using the PCMCIA control page option (or the PCMCIA symbol in your systray) before physically ejecting the card.
How can I get a node set up on my property?
Check out the GetStarted page and set one up. This network is owned by the users. The addresses are manually assigned to each of the routing nodes on the SWN.
What equipment do I need to start a node and what is the cost?
There are several methods to set up a node. Cost is a varying factor depending on if you provide services or are simply a user. Check the NodeHowTo for details on each node.
Where do I get equipment?
It depends on what equipment you need. If you have an old 486 or Pentium class computer laying around, you're halfway there. Wireless cards can be found on http://www.ebay.com/ or through many other sources such as a computing goods store or online price-comparison website. Antennas can be built or purchased from a variety of sources. Check UsefulLinks for an index of links and visit WirelessHardwareLinks for a more extensive rundown on vendors and plans. HotNews occasionally has notices on vendors having special sales.
What about FCC Regulations? Are antennas and amplifiers legal?
My AP has two antennas. Can I attach two different antennas to it (a directional and an omni)?
- You can but it will not work like you might think. Your AP has "diversity antennas". Essentially diversity antennas are designed to allow better coverage under the assumption that one of the two antennae will be in a better position. To be effective, both antennas need to be the same and located relatively close to each other. Also if you have a Linksys router with updated firmware, you can select only the right or left antenna to be active, or disable diversity spread altogether, and divide the power between the antennas.(left is left when standing behind it, not looking at it). Diversity is most often present in AP units but some client cards also have diversity. In client cards, diversity is only partially implemented by the chipset. For example, the Prism chipset only uses diversity when receiving. For transmitting, the Prism chipset directs output to one of the antenna and never chooses the other. So, if one of the antenna is highly different, you might get unexpected results with a Prism chipset....
Which wireless cards do you recommend?
Take a look at the HardwareComparison page. There are all sorts of cards available and there may be one that fits your needs best. Any card that is 802.11b compliant will work. The Lucent Orinoco (and Lucent re-branded cards such as Sony) seem to work very well and they have external antenna adapters. The Cisco cards also work well. If you are looking to use the HostAP drivers under Linux then you need a card that uses the Prism chipset such as D-Link or Linksys. Many others use that chip set also.
Prior to 2001, most cards were of the 30mW output power type. In 2001, more cards became available with higher output power. Some of these cards, such as Senao (see SenaoCard), have both greater sensitivity and/or power and are considered by many to be among the best cards to use if you need greater range. For security reasons, if you don't need long range, low power cards are preferred so that your signal won't be picked up at a long distance by someone else.
What kind of antennas are you using on your access points?
For more info check out the WirelessHardwareLinks, AntennaHowTo, and the PointToPoint pages. There is no one antenna to use because the situations at each location vary. PointToPoint links need a DirectionalAntenna such as a DirectionalParabolic or a DirectionalYagi. To cover your house, use a OmniDirectionalAntenna or DirectionalSector. Pick whatever is right for your needs and budget. Some background info on remote antennas is also at RoofTopAdHoc and WirelessHardwareLinks. It is possible to put parabolic reflectors on access points that have permanent non-removable antenna to make them more directional.
Can I swap the firmware on my AccessPoint?
Yes, you can easily swap the firmware on your Lucent baseed APs, like the OrinocoAp1000, OrinocoAp500, OrinocoRg1000, and AppleAirport. PersonalTelco and some people on the dev list have swapped the firmware on an OrinocoRg1000 with that from an OrinocoAp500. It is also possible to turn the OrinocoRg1000 into an AppleAirport. Check out ApFirmwareSwapping for details. This is also possible with the Linksys, SMC, and Netgear APs as well....
How can I improve the performance (of my antenna) ?
- Well, that is a loaded question. If what you mean is to improve your overall performance (throughput), then there are a large number of variables that can be influenced. You can affect some items that might improve the throughput. These are: the position of your client antenna, transmission line losses between your client card and the client antenna, antenna type, antenna gain, and reduction of interference.
If what you meant was very purely about improving the performance of just the existing antenna (not the transmission line, type of antenna, etc) that you are currently using, well, that is more difficult. You can raise or lower the antenna's height so that the radiation pattern is improved, add a groundplane to the omnidirectional antenna, reduce interference, or even change the radiation pattern of an omnidirectional antenna as shown here. Yes, it is possible (and is done with access points) to add a parabolic reflector to an existing omni in order to obtain more gain in a certain direction. Items that affect overall performance include: (1) High insertion loss in the front end (2) Poor antenna matching (3) Pickup of interfering signals.
High insertion loss can result from cable attenuation loss, connectors, bad connections, etcetera. Typically, each time you have a connection, there is signal loss; each connector introduces signal loss. This is why use of PigTails is undesirable if you can just directly connect the antenna to the 802.11 device. Each pig tail introduces two connections and each of those connections is another opportunity for signal loss. Also, note that not all connectors and cables are made for use at microwave frequencies. Cheap connectors might be made with insulating material that is only partially insulating at microwave frequencies. Poor antenna matching losses result from mismatched parts in the transmission line, bad connections, an antenna that is not impendance matched, lack of sufficient ground plane for an omnidirectional antenna, etcetera. Typically, 50 ohm impedance transmission line is used, but some people might mistakenly use 75 ohm cable from communication or cable tv supply sources. Some connectors also introduce signal discontinuities as well which affect the SWR. Good antennas often try to have a sub-multiple or multiple of the wavelength which is why some antenna will have loading coils as opposed to simpler antennas which don't. Pickup of interfering signals will lower your effective throughput. This might be from other devices in the same frequency range such as a microwave oven, 2.4Ghz cordless phone, or a device being operated by your neighbor. This is why having a high-powered 802.11 device is not always desirable; it can cause interference to your neighbors and lower their own 802.11 device performance. Using only as much power as necessary is desirable; for most people, the 30mW output of an Orinoco is sufficient. If you know the source of interference, you can use a directional antenna aimed in a direction that won't pickup the interfering signal.
Questions About Nodes
Can I set up a link using a directional antenna pointed at an omni antenna
- Yep. It would be very easy to set up a link like that. In fact you can set up an omni antenna with many directional antennas pointed at it. This is a point to multi-point link. However, sometimes in multipath and high noise environments, omni directional antennas used in place of a directional antenna can yield a degredation in performance. This is because an omni directional antenna will receive RF from every direction. A reflection from a building coming from behind or a cluster of microwaves in the condo down the street will mix with your intended signal, raising the SNR or destroying random frames.
Can I run a really long coax cable from my machine to an antenna on my roof?
You could if you want, but cable can be very lossy especially if it is carrying a microwave frequency signal. In an SWN node, coax is used to carry the microwave signal (2.4GHz) from the power amplifier to the antenna. This is a very difficult task; one that is far more susceptible to loss than that of transferring digital signals over an ethernet cable. This means if you run more than 10 feet/3 meters or so of coaxial cable, most of the 30 mW of power coming out of your card will be absorbed by the time it gets to the antenna. You can use special cable with low Frequency loss (typically 6dB/100ft - 6dB/30m) which cost (typically 0.75$/ft - 2.50$/meter) Calculate your Attenuation. Also remember that every connector you add to your run is 0.25 dB loss. Another approach is to use a USB broadcast unit as mentioned at RoofTopAdHoc ,or you can check out examples of some outdoor modifications from PatrasWirelessNetwork in Greece http://www.patraswireless.net/devices.html. Of note is that one installation uses USB repeater extension cables.
The Antenna Cable Comparison chart lists the attenuation of a lot of common types of coax. The lower the attenuation, the less loss.
Instead of having a long transmission line, what most people opt for is to locate the access point close to the antenna and use a long ethernet Cat5 line to the access point. It is much more practical to have a long ethernet Cat5 line than a long microwave transmission line. If there is no convenient power source for the access point, the PoE or power-over-ethernet approach is used.
I want to build my own antenna. What is the best one for me to build?
There are a lot of different designs out there. For a good comparison of them read 802.11b Homebrew Antenna Shootout and the Antenna Comparison Testing. However, the Cantenna is the first choice of an easy to make antenna with examples in CookieCantenna and PringlesCantenna. Before you build one, you may want to read AntennaHowTo.
How the heck do I mount an antenna? I don't have any masts on my roof or anything...
There are a few ways to mount antennas. The easiest of course, is bolting to a mast, chimney or tower. There are several kits for this sort of thing available for TV Antennas so you can go to the local hardware store and pick one up for under $50. If you have a flat roof (and dont want to drill holes or put up a permanent mount) you may want to build a self standing pole or tripod setup and sandbag it. See WaterProofBoxes and AntennasOnTripods for a few examples of how you can do this.
In some cases you can make good wireless connections without going up to your roof. For example, if you have good LineOfSight to another node from an upstairs window, you may be able to keep all your equipment indoors using IndoorAdHoc ideas. Also, flat panel antennas (sector or patch) can be mounted on walls or inside your attic without any need for a mast. Of course, these are not omnidirectional solutions to which a mast is well suited for. However, omnidirectional antennas are not always needed depending on your location...
What protocols are we using?
IEEE 802.11b (WiFiStandard), TCP/IP.
What radio band are we using?
- 802.11b operates on the 2.4GHz ISM band, which does not require a license in the US. By combining 5 channels we can achieve up to 11Mbs of bandwidth per cell.
What hardware and software is required to connect to the network?
Each ClientNode must have an 802.11b-compliant transceiver, typically a PCMCIA card. There's pretty good lineup of what's available in our HardwareComparison page. Tunneling and mobile IP software is To Be Determined (TBD).
Nodes may have additional software and hardware, depending on their function. Most of this is TBD. The goal is to build low-cost infrastructure based on open-sourced software and hardware. Check UsefulLinks for more details on hardware and software.
Which IP ranges are used?
The network wireless network will use a portion of the 10.0.0.0/8 reserved IPv4 address space, see IpAllocation for more details. We are building the network with non-internet-routeable IP's for a couple of different reasons. One is due to the portability of this address space. Another is logistic, if we were to BGP announce on the internet from multiple egress points, it would require a huge amount of coordination and would place control in those central points.
What nodes are available for access?
How does routing work?
For a general description of routing, see RoutingForBeginners
If you are interested in the technical details, many of them are still being worked out at HackNight. For the most part, we are using Zebra 0.93a with RIP, OSPF, and BGP.
Will there be DNS services?
How are clients authenticated to the network?
- All access is free and unencrypted to all. Of course, you may tunnel through the 10.net LAN to your destination using any number of schemes. In other words, clients are not authenticated to the network, and security is up to you. Caveat emptor.
How do I access the Internet?
Can I roam?
- Yes. In theory. In practice there aren't any two nodes close enough for you to be able to move between them with out first hitting a big area with no coverage. In practice, your wireless drivers do not automatically hand-off access to another node, so "roaming" outside of the range of your current node will result in a disconnect. To connect to another node, users typically have to manually select a node for connection. So, roaming doesn't mean that you have the automatic connection to a new node as you do with cellular phone nodes.
Can a 802.11 node be a repeater?
Can WiFi links use other user's nodes as relays (like Ax.25 amateur packet radio does) when no direct view to the next AP is available? That would solve quite some problems
here on my project - but is it implemented in any WiFi protocol? - Johan (wifimassatois@free(spam?no).fr
WiFi links can be used to route packets between nodes that are not otherwise in direct communication range with each other. For fixed nodes (computers that don't move) the OSPF routing protocol that Zebra implements can do the trick. For nodes that move, other protocols have been developed to support such a Mobile Ad Hoc Network (MANET). A Google search on MANET or the names of some protocols (e.g., Dynamic Source Routing (DSR) or AODV) will return hits including implementations of the protocols that you can run. The problem comes in convincing all your friends to run the same protocol. If you each run different routing protocols, the nodes won't discover the existence of each other. (as an author of DSR, I'm biased, but I think it's a great protocol. -dam)
What's with this 42 thing? I can't find an 802.42 spec or anything
Read The Hitchhiker's Guide to the Galaxy by the late Douglas Adams. It explains it pretty well, and is a very funny book to boot.
Any plans for 802.11a or 802.11g?
The SeattleWireless network is not limited to 802.11b. Any wireless networking medium, 801.11b, 802.11a, 802.11g, 802.11n, 802.16, laser, packet radio, etc., can be used as long as it functions with the rest of the network. We are mostly focusing on 802.11b at this point because the hardware is available, cheap, and widely-used by members and users who have 802.11b cards for their laptops. At this time, moving to 802.11g doesn't yield any new understanding in developing the network, and 802.11n is a new IEEE standard too new for easily purchaseable consumer hardware.
How do I use the laptop in the car more conveniently?
There are many approaches to improving the ergonomics of using a laptop in a car. There are perhaps three major online companies selling solutions. One method uses a stand fastened to the chair rail. Another method rests on the passenger seat and has adjustable risers and swing arm. And another method sits on the steering wheel. StartideRising uses a Deskdrive since it is cheap, easily portable, and puts the laptop on the steering wheel. Other types of solutions are available at A2Z Solutions. A2Z Solutions has products that you can use to mount your laptop (and be able to look/use it while driving) such as the Mobile Laptop mounts. JEFA Tech sells a mobile Omni Magmount antenna to get your signal out of the car. http://www.jefatech.com. Note that using a laptop whilst driving is illegal in Washington State, although looking at the screen is probably not illegal. However, having a securely mounted laptop on a laptop stand is convenient if you just so happen to pull over and use it.
How safe is the microwave radiation from 802.11 devices?
There is a lot of controversy in this area. Sadly, fears have been overhyped by junk science and scientific studies as of late. There is no conclusive evidence that low powered non-ionizing radiation can cause damange to human cells as of yet. Wavelengths are *far* too large to cause damage to cell structures, brain tissue, DNA structures, and proteins. This means that it is highly unlikely that radiowaves can be linked to cancer. (These destructive effects come into play when you get into the X-Ray range, since the wavelength can have the width of a protein's helix-alpha or DNA)
There is one thing that is certain: high levels of radio non-ionizing radiation can cause burns. When radiowaves transverse matter, heat is produced. These cummulative effects are not seen unless matter exists in close proximity of an antenna emitting tens or hundreds of watts. Thankfully, the FCC and ANSI have done a lot of work in this field to determine what is safe and what is not safe.
Naturally, 802.11b laptop cards are far from exceeding these levels. Maintaining a distance of at least 1-4 feet from even the highest EIRP unlicensed 2.4GHz antennas exceeds several times the recomended distance according to the FCC.
The Federal Communication Commission (FCC) sets guidelines for Maximum Permissible Exposure (MPE) for microwave frequency radiation. Section FCC 1.1310 specifies criteria used in evaluating environmental exposure to microwave radiation as indicated in section FCC 1.1307(b)!
Why is the sky blue?
The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.
However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.
What is the airspeed velocity of an unladen swallow?
African or European? I don't know that! AAAAAAHHHHHHH!!!
Or you can take a look at Estimating the Airspeed Velocity of an Unladen Swallow