Ask the Wi-Fi Guru, Episode XV

By Aaron Weiss

May 08, 2009

In our May 2009 installment of this monthly Q&A series, the Wi-Fi Guru covers a wide variety of Wi-Fi networking issues, including signal boosters, dealing with foliage-based interference (ah, spring!), and resolving basic connection problems.

awhead.pngApril showers bring May flowers—and also, if you live in the northern climes, leaves. In the northeastern US, everything turns green in May, which for us humans is inspiring and invigorating. But if you are a wireless router associating with clients throughout the great outdoors, leaves can be your worst enemy. Unfortunately, mother nature has arranged things such that the frequencies we commonly use for wireless networking, such as 2.4 GHz, tend to be blocked by greenery.

If you have any wireless links running shooting through trees or bushes, especially those you setup in the fall or winter, check for changes in signal strength. You may find that signal varies as an offending branch blows in the wind, moving in and out of your router's line of sight.

Sometimes the only remedy from leaf blockage is strategic pruning (or, in severe cases, a chainsaw), but before resorting to arboreal butchery consider outfitting grid or parabolic antennas at each end of your wireless link. Highly directional antennas will require precise aiming to maximize signal, but can produce stronger signals through a difficult environment than omnidirectional antennas (such as those included with most routers).

Q: I intend to set up an IP camera video surveillance system for two ice plants located about 200 meters away from each other. Would a second DD-WRT router (like the Linksys WRT54G) be enough without installing a repeater in-between? You said installing a repeater would reduce the bandwidth, so I want to maintain it as much as possible. The first router is located in a single-story office (which is just very near the first ice plant) with no tall buildings nor lots of trees in between.--Edgar


A: Would you accept a firm answer of "maybe"? There are several factors to consider here, although one way or another there is a solution that will work.

The typical rating for a Wi-Fi link is a maximum of just over 300 feet (or 100 meters). Several factors can increase this range, including power output and antenna strength. You're looking at over 600 feet between the two buildings, which is long, but in practice, a distance that can probably be reached with good antennas and minimal obstructions.

Keep in mind, however, that Wi-Fi links are not either-or. The wireless client—in this case your IP camera—negotiates a speed with the wireless router based on signal conditions.

Suppose the maximum rated speed of your router is 54Mbps. A client 600 feet away might be able to grab a signal, but it could be so low that the established link is only 11Mbps or less. Although it's true that repeating the signal with an additional router halves the available maximum bandwidth, you might still come out ahead—a repeater that is close enough to ice plant 2 to deliver a strong signal might be able to negotiate a faster net rate—say, 24Mbps—than trying to make the long link without a repeater.

If your repeater router can be outfitted with a replacement antenna (such as WRT54G models prior to V8), your options improve considerably (especially if your IP camera is stuck with its integrated antenna).

The first scenario I would try would be to use your second router as your one and only repeater. Your primary router is located in an office adjacent to ice plant 1. The IP camera in ice plant may or may not be able to associate directly with the primary router (we don't know how far it is or how the buildings are configured). So, I would place router 2 at the far end of ice plant 1—that is, closest to ice plant 2.

Assuming that your routers are all roughly at a similar height from the ground, a pair of good omnidirectional antennas installed on router 2 may allow it to "see" both your primary router and the IP camera in ice plant 2. Flash router 2 with DD-WRT and try to setup a WDS link between it and your primary router. You might also experiment with increasing the power output on router 2—although the DD-WRT default is 42mW, you can set it much higher. Be careful here—too much power will increase noise and potentially overheat the router. User reports suggest you could go up to 100-150mW, but you do this at your own risk (well, at the router's risk).

Should omnidirectional antennas not provide strong enough signal strength between router 2 and both your primary router and ice plant 2, consider directional antennas. These will provide much greater range, but across a much narrower line of sight—meaning you would need to aim router 2 with more precision.

Even if you wind up spending more money to outfit your primary and secondary routers with more powerful antennas—money you could spend on a third router—relying on better antennas rather than a third repeater will help you achieve maximum signal strength without the bandwidth cost of another repeater.

More resources: "The Open Source WRT54G Story," "How to Choose the Best WRT54G Router for You," "DD-WRT Tutorial 2: Extend Range with WDS."

Q: I have a PS3 and a Nintendo Wii and I use my neighbor's Wi-Fi to use the ‘Net.  My question is, can I boost his signal from my apartment without plugging into his router? --Jack


A: Let's assume, for the sake of ethics and neighborliness, that the prior conversation with your neighbor went something like this...

You: "Hey neighbor, can I use your Wi-Fi signal for my PS3 and Nintendo Wii? In return, I will walk your dog!"

Neighbor: "Sure you can use my Wi-Fi signal, but I don't have a dog."

You: "Thanks! Can I plug into your router to boost your signal?"

Neighbor: "Nope!"

So the question is, how would a totally ethical person behaving entirely on the up-and-up improve signal reception from a generous and fully-informed neighbor?

If you haven't already, I would connect the PS3 and Wii to a router (by wired Ethernet if possible, for the sake of ease), such as the WRT54G. I would flash the router with DD-WRT or Tomato (or another firmware of your liking), and replace the router's antenna with a directional antenna. See above answer. Then aim the directional antenna with precision toward your neighbor's router. Assuming you know where it is. Which you do, because he invited you in for coffee and showed it to you when you asked kindly to share his connection.

More resources: "Wi-Fi Planet's Greatest Hits: DD-WRT," "Introduction to Tomato Firmware," "Ask the Wi-Fi Guru, Episode XII."

Q: I can't get the Internet when I am connected to my router, but when I am connected from my modem to my PC I have no problem getting on the Internet, what should I do? --Eddie


A: Let's suppose you have a cable modem. When you plug your PC into your cable modem, the Internet works dandy. But when you plug your router into your cable modem, and then your PC into your router, no more Internet.

Could be so many things. Perhaps the router is misconfigured—maybe DHCP is not enabled, or maybe your cable provider requires authentication with a login that needs to be configured on the router. Without more information it is impossible to know more about your specific situation. But this question brings to mind two somewhat common problems that would produce this same scenario.

Scenario 1: Your cable provider requires MAC address authentication. Some cable providers (such as Comcast) authorize a specific PC to connect to your cable modem. They do this when the account is setup, programming the cable modem to recognize only the MAC address for your PC. When you plug the router into the cable modem, it sees a different MAC address and refuses to open the Internet connection.

The typical solution to this is by cloning your MAC address on your router. Many routers now support this. The exact process varies by model, but basically you will connect your authorized computer to the router, open the router's administration interface, and find the setting for "clone MAC address." The router will then copy the MAC from your computer and present that identifier to the cable modem, effectively mimicking your authorized PC. (Considering how trivially easy and widely supported this is, one wonders why cable providers even bother trying to impose this "limitation").

If you are using a laptop, it probably has both a wired and wireless network connection. Keep in mind that each has its own MAC address—so if your wired connection is how the modem was authorized, you'll need to perform the cloning procedure using the wired connection to your router. (Once the router is online with the cable modem, you can then go wireless.)

Scenario 2: Your cable provider supplied you with a crossover cable to connect your modem to your computer. A crossover cable looks just like a "normal" (aka "straight through") Ethernet cable, but it is wired slightly differently, designed to directly connect two devices without a hub or switch (like a router) in between. Some crossover cables will have markings on them that say "crossover," but not always.

Normally you use a straight through Ethernet cable between your router and any other device—in this case, the cable modem and/or your computer (unless it is wireless). Some routers have a switch to let you use a crossover cable for the link to the cable modem; other routers can auto-sense and adapt accordingly. But some have neither feature and will not connect properly to the cable modem using a crossover cable—in which case, ditch the cable provided with your modem and acquire a "normal" Ethernet cable.

More resources: "Ask the Wi-Fi Guru, Episode XII," "Review: Elektron 2.0 RADIUS Server," "Ask the Wi-Fi Guru, Episode VIII." See also "What's a MAC Address, and How Do You Find It?" at our sister site, SmallBusinessComputing.com.

---

Finally, last month we ran some questions in search of ideas from you—our brilliant readers. One question involved setting up a simple hotspot that included support for a splash screen and bandwidth limiting. A reader named "John" wrote in to say:

"Meraki (www.meraki.com) sells a line of routers/repeaters that may be helpful to both Jason and Ron (from your column of 4/17/09). Meraki's routers do support bandwidth limits and splash screens using a simple Web interface. And you can add any number of additional units as repeaters to extend the range of the hotspot. (No, I don't work for Meraki—I just use their products.)"

Thank you, John.

More resources: "Ask the Wi-Fi Guru, Episode III," "Review: Meraki Mini and Outdoor Router/Repeaters," "How to: Set up a Wi-Fi Hotzone Using Meraki (Part I)."

Aaron Weiss is a freelance writer, book author, and Wi-Fi enthusiast based in upstate New York. To submit your questions to the Wi-Fi Guru, simply click on his byline (above) and put "Wi-Fi Guru" in the subject line. Click here to read last month's column. For more by Aaron Weiss, read "How to: Monitor Bandwidth with Tomato Firmware." For definitions of unfamiliar term, visit our searchable glossary.

Originally published on .

Comment and Contribute
(Maximum characters: 1200). You have
characters left.