By Aaron Weiss
November 12, 2008
In the November 2008 installment of our monthly Q&A; series, the Wi-Fi Guru covers SSIDs, OpenWRT, and cordless phone interference to help a home user, a college student, and an entrepreneur with their Wi-Fi dilemmas.
- Ask the Wi-Fi Guru, Episode VIII
- Ask the Wi-Fi Guru, Episode VI
- Ask the Wi-Fi Guru, Episode V
- Ask the Wi-Fi Guru, Episode IV
In the November 2008 installment of our monthly Q&A series, the Wi-Fi Guru covers SSIDs, OpenWRT, and cordless phone interference to help a college student, an entrepreneur, and a home user with their Wi-Fi dilemmas.
Q: It seems my AT&T ID-2820 2.4 GHz cordless phone broadcasts a buzzing noise. But my ears don’t actually hear it. All this stops, if I move the phone away from other devices, but that is inconvenient. – John
A: Do you remember when we did not have cordless phones everywhere? Handsets tethered to their base with that curly cord that let you pace and roam only a few feet in each direction. We lived like cavemen. But now phones are wireless. Unfortunately, so is almost everything else. There is only so much wireless spectrum to go around.
In this column we spend a lot of time talking about wireless networking, and in nearly all cases we are talking about RF in the 2.4 GHz frequency band. The 2.4 band is very popular with many wireless devices because it strikes a good balance between distance and energy consumption. Because the U.S. government does not require a license to operate in the 2.4 GHz frequency range, manufacturers can make a wide variety of low-cost products that communicate on basically the same frequencies. The result? Think L.A. freeway at rush hour. (Or any time, really.)
Within the 2.4 GHz range there are 11 commonly used channels, each operating 5 MHz apart from one another. The footprint of a particular wireless device will usually be wider than a single channel, however. What this means is that not only can devices operating on the same channel interfere with one another, but even devices operating on adjacent or nearly-adjacent channels can also cause interference.
Cordless phones operating at 2.4 GHz often hop across multiple channels during normal operation to ensure for themselves a clear signal. Like an aggressive driver weaving across every lane, their signal path is all over the road. Most 2.4 GHz devices, including wireless networks, are designed to tolerate a certain amount of interference, but beyond their tolerances you may experience slow or dropped connections and other weird behaviors. Likewise, cordless phones and other wireless devices may pick up signals from wireless networks and express them through noises and hums.
Because the 2.4 GHz is so crowded these days (did I mention baby monitors, alarm systems, and microwave ovens?!), the most prudent choice in cordless phones is actually a 5.8 GHz or above model. Do note that some phones advertised as 5.8 actually use 2.4 GHz to communicate with their base stations—what you really want is a “true” 5.8 GHZ or higher phone. Some models are more up-front with this information than others, unfortunately.
- For more on cordless phones, read “Dueling with Cordless Phones,” “Interference from Cordless Phones,” and “Minimize WLAN Interference.”
Q: I’m a college student living in an on-campus dorm. All the rooms are set up for a hard-wired connection, but I hate having wires all over the place. The second day, my roommate, a computer science major, set up a non-broadcasting network with his router, so as not to interfere with anything else. Our Internet was soon cut off [by the college]. The tech office discovered our router and told us we couldn’t use it…unless we could set it up not to interfere with the network that already exists for the dorm, even though the dorm network doesn’t work at all. He mentioned something about an NTSC, or similar acronym, that could be turned off to prevent interference with the network. — Michael
A: The Guru remembers being a college student living in an on-campus dorm. In my day, we didn’t have wireless Internet either. We had modems. Dial-up modems. They connected to the phone line and were powered by steam. On cold mornings, our steam-powered dial-up modems had to be cranked by hand just to get connected. But you, you kids today, with your high-speed broadband and your clean water. (Did I mention that our water was a strange color?)
Fortunately the spirit of rebellion lives on. In the annals of collegiate mischief, connecting a secret wireless router to your dorm Ethernet might not rank up there with impaling a pumpkin on a clock tower, but still—fight the man! Speaking of the man, it is likely that the acronym he mentioned was actually SSID (NTSC is a television broadcast standard, and it isn’t even digital, so blech.)
It sounds like your dorm already has a wireless network in place, although you say it does not work well. This network has a name, also known as an SSID (“service set identifier”), let’s call it crappydormnet. This name is being broadcast by the dorm’s access points (AP’s).
Your wireless router is presumably also broadcasting an SSID, let’s call it twofunguyz. You say that your roommate set it up as a “non-broadcasting” network, but the facts don’t entirely add up. It sounds like the tech office detected your SSID being broadcast, which is likely how they found you running the router. They seem to be asking for you to disable SSID broadcasting. (There are other ways they could have detected your router, but SSID broadcasting is the most probable.)
Most wireless routers include an option in their wireless setup menu to disable SSID. If you do this, you will need to configure the wireless clients on your PC’s to know the SSID they are connecting to, since they will not see it with a scan of available networks. The details for this vary depending on your wireless computer, and if it runs Windows or OS X.
How does hiding your SSID prevent your wireless network from “interfering” with the dorm network, as per your tech office claim? It doesn’t, really, unless you had named your wireless network the same as the dorm network. Don’t do that. It is possible that the tech office was concerned that if students were connecting to your wireless network rather than theirs, too many users might be crowding the connection to a single dorm room.
It is also possible that the tech office is concerned about the frequency channel your wireless router is using. There are three wireless channels that will not overlap—1, 6, and 11. When you scan for available networks and you find the dorm wireless, you should see which channel it is broadcasting on (6 is very common). You can configure your wireless to broadcast on a separate channel—1 or 11 would be good choices if the dorm net is on 6.
Between hiding your SSID and selecting a maximally non-interfering channel, maybe the tech office will be satisfied and restore your network connection. Or maybe you just need to invite them to your next party. That’s probably what they wanted in the first place.
- For more on SSIDs, read “What SSID is Right for You?,” “Getting Phished: Why SSID Spoofing (Still) Matters,” and “Your SSID Isn’t Hidden Forever.”
Q: I am setting up a café that offers free Internet. I need to set up a splash screen for legal reasons. I would like to have everything loaded on the router if possible. I heard that OpenWRT is the way to go, so I’m looking for easy/detailed instructions on how to load the software and Web page (splash screen) onto the router.–Jose
A: Readers of this column will often see recommendations to DD-WRT and, increasingly, Tomato. Both are firmware for wireless routers that replace the stock firmware shipped by the vendor and offer enhanced functionality. OpenWRT is another such firmware. It tends to attract more advanced users because it does not include a GUI (graphical user interface), while both DD-WRT and especially Tomato are point-and-click friendly.
Creating a splash screen for a public hotspot like an Internet cafe is very possible using DD-WRT. In fact, you can find a tutorial on doing exactly this right here. You’ll notice in the tutorial that it is easier to configure a splash screen if the HTML for your page is hosted on a public server. It is possible to store the page inside the router’s filesystem, but working with your router’s embedded filesystem requires an additional level of expertise.
Since your concern is that you don’t want to use any hardware beside the router, why not host your splash page at a free Web host, like Yahoo GeoCities or Google Sites? No extra gear necessary, and it will be easier to maintain or update the splash page on a public site than loaded into the router’s filesystem.
- For more on Tomato, read “Introduction to Tomato Firmware.”
- For more on DD-WRT, read “Beyond the WRT54G: DD-WRT for Many Flavors of Hardware,” “DD-WRT Goes Major Label with Buffalo Technology,” and “Wi-Fi Planet Compendium of DD-WRT.”