Ask the Wi-Fi Guru, Episode VII

By Aaron Weiss

September 05, 2008

In the September 2008 edition of our monthly Q&A column, our Wi-Fi Guru focuses on helping readers solve issues involving the placement, configuration, and compatibility of multiple routers in one household.

awhead.pngIf there is any theme to this month's episode of Ask the Wi-Fi Guru—and I'm not saying there is—it is that the era of the two-router household is almost certainly upon us. Years ago—before you were born, if you're lucky—people used to own only one TV. And by people, I mean, whole families. One TV. You can imagine what that must have been like, watching TV with other people—people related to you, no less—sitting right there in the very same room. It was a difficult time to be alive, let's just put it that way.

Not so long ago, people owned one wireless router and they were happy to have it. But one wireless router only goes so far—literally. And that's the problem. In many cases, an effective way to increase your wireless range in home or office is to add another router. They're cheap now. It's nothing to be ashamed of. There is more than one way to do it, as you'll see in this month's column.

Q: I am trying to use WRT54Gv2/DD-WRTv24 antenna selection to have one antenna TX and the other RX.  Does the menu option where you can select TX/RX and Left/Right antennas really do what it says?  Namely can I have one antenna exclusively for TX and the other exclusively for RX. – Petar

A: Truth in advertising—it is indeed true that DD-WRT lets you manually select which of the two WRT54G antennas is assigned to sending (TX) and receiving (RX). More interesting still is not so much that you can, but why would you want to? It turns out there are several reasons one might do this, some useful and some perhaps not so much.

First, it is important to clarify that wireless radios operate in half-duplex mode—they cannot send and receive data at the same time. Instead, they switch between sending and receiving modes. Furthermore, only one antenna is used for sending. Routers that have two antennas (some have only one) are using "diversity" reception, which means that they dynamically switch between them to pickup the strongest signal, which may vary due to myriad environmental factors including multipath interference and reflection.

Diversity mode is used for a reason, so if you are simply using the stock "rubber ducky" antennas included with your router, there really is no advantage to manually assigning TX and RX to exclusive antennas, and effectively disabling diversity. However, in some scenarios you want to replace the stock antenna with a high-powered directional like a grid or yagi. Typically, this is done to create a long range wireless link, say between houses or office buildings. In this setup, you want to assign both TX and RX to the directional antenna and not bother with the second stock antenna—and this is where DD-WRT's setting can become very useful, since the stock firmware does not let you make such an assignment.

Oh, and you might be wondering—which antenna is the left one? The right one? With DD-WRT, left and right are based on looking at the router from the front, where the LED's are. However, other firmware might use the reverse orientation, looking at the router from the back. Of course, you have a 50% chance of guessing correctly, but to be sure, simply remove one antenna, and change the RX/TX assignments to see whether "left" or "right" works with just the one antenna.

Q: I am connected by Time Warner Cable to my system through a Linksys WRT54GL router. I put on Tomato firmware and am transmitting at 84mW. This set up is in the front of my house on the second floor. My basement is in the rear of my house. When I'm in the basement, my laptop seems to pick up a better signal than my PC, but the speed it about 25% of upstairs. What can I do to get a stronger signal wirelessly down in the basement? Someone suggested using two routers, namely an n-draft router upstairs and placing my Linksys on the main floor just above my basement in my dining room. Is Tomato good firmware to use or should I install DD-WRT on a router upstairs as well as the Linksys? – Arthur


A: For those readers who haven't yet heard of "Tomato," it is not only a nutritious and delicious vegetable (technically a fruit, but that's for some other guru to explain)—Tomato is also an open source firmware, like DD-WRT. In fact, we will be running a tutorial on using Tomato in the near future, so check back soon!

Where was I? It doesn't sound like the firmware is the problem in this situation. Whether you are using Tomato or DD-WRT, the challenge here is primarily environmental. Basements are especially challenging for reception of wireless signals, and in this case your router is two floors away. Bumping the transmit power to 84mW (the default is 28mW) is probably hurting more than helping—when you increase power, you increase both signal and noise. The reason your connection speed is reduced by ¾ is because your basement PC cannot negotiate a faster rate, which may in part be due to interference from the extra noise.

The suggestion you received is basically to add a second router into the mix, effectively re-distributing your wireless signal. You could do this—there is more than one way to get it done. Using an n-draft router might offer some slight advantage for getting maximum signal to a router on your main floor, only because the n router will be using a superior MIMO antenna array; but your Linksys is not an n router, and so the benefit of doing this is not hugely compelling. Chances are that a second router just like your Linksys will do the job.

If your second router supports WDS (wireless distribution system) you may not even have to muck around with flashing an alternative firmware (some stock routers support WDS out of the box). You can setup WDS between your new router and your Tomato-based router, which should improve the signal to your basement.

It may be heresy to say this, but I've said it before so there's no turning back now—what about not going wireless to your basement? If you plan on living in this house for a long time, I would consider running Ethernet from the second floor to another router in the basement. Maybe even along the outer wall if it would be an easier install. In the long run (get it? long run!), this would be the most stable and fastest solution, particularly if you want to run a gigabit LAN.

A third option would be to cable only from the second floor to first floor—see the question and answer below for a similar scenario.

Q: I was using my Linksys as my main router, but I'm using a Netgear router now. I still use my Linksys as an access point by turning off the DHCP and just plugging the cable into one of the four LAN ports. Now that I'm using DD-WRT, I wanted to make another open Wi-Fi point, but it's not working. -- Dave


A: The good news is that what you are trying to do—configure a second router as a "dumb" wired access point—is perfectly legitimate. The bad news is that it isn't working. But it should, so we can take solace in that there must be a simple configuration oversight somewhere.

You were right to disable the DHCP server on your second (AP) router. When it comes to DHCP servers on a LAN, you must always apply "The Highlander Rule"—there can be only one. But that's not all—it is also a good idea to disable the firewall on your AP router. Security should be handled by the gateway (primary) router.

It sounds like your cable is plugged into the correct port—it must be a "LAN" port, and not the "WAN" or "Internet" port on the AP router. (You will not use the WAN/Internet port.) This also means that your AP router is not going to receive a DHCP assignment from your primary router, because it only listens for DHCP on its WAN/Internet port. You will need to manually configure your AP router's network address using an IP that is compatible with your primary router.

For example, suppose your primary router has the typical IP of 192.168.1.1 (and network mask 255.255.255.0). On your AP router, you will configure it with an IP address like 192.168.1.2 (same network mask). You may or may not need to specify an IP for gateway and DNS, but if you do, it is the IP of your primary router (192.168.1.1 in this example).

For testing purposes, at least, you should also configure the wireless SSID on your AP router without any WEP/WPA/WPA2 security. You can apply the security of your choosing after verifying the AP connection.

Wireless clients who associate with your AP should receive their IP address and related settings (gateway, DNS) from your primary router. And you should be able to connect to your AP router using the IP address you manually assigned to it.

Aaron Weiss is a freelance writer, editor, and Wi-Fi enthusiast based in upstate New York. To submit your questions to the Wi-Fi Guru, simply click on Aaron's byline and put "Wi-Fi Guru" in the subject line. Click here to read last month's column.



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