Ask the Wi-Fi Guru, Episode XIII

By Aaron Weiss

March 03, 2009

In our lucky 13th installment of this monthly Q&A series, the Wi-Fi Guru helps with wireless bridges, Hi-Def home networking over 802.11n, and some DD-WRT issues.

This month the Wi-Fi Guru laughs in the face of superstition. It is episode 13, you see, and if we were an airplane we might skip row 13. If we were an apartment building we might not have a 13th floor. If we were a residential street there would be no house marked number 13. But when you face down wireless networking problems month after month, you develop something important—bad posture. But also, a backbone, and though it may be gnarled and curled from sitting in an office chair all day, it gives you courage—courage to look at the number 13 and say "ha" right to its face. So, let's start a new superstition instead. For example, if your wireless router blinks 7 lights at the same time, that means a black cat will break a mirror while walking under a ladder.

Q: I have a weak signal from Optimum's Wi-Fi network on Long Island. I can access with my laptop when near the street, but I frequently lose signal, and would also not like to spend my time on the street(!). Do you know of a device, or a way to configure a typical Linksys router to act as a signal repeater for this type of situation? Also, this "free" service is available to Optimum Internet users (I am one at home) and they ask for a log in (e-mail address and password) when accessing the service. So, I guess it's really a two-part question: Can I configure a device to act as a repeater; and, can the service be "nailed up" once I am able to "see" the network through the repeater or access point? – Mark

A: Optimum Online is a cable ISP operating on New York's Long Island. In addition to the usual cable broadband services, though, Optimum subscribers can get online through one of thousands of hotspots, using their account login. Seeing as the Guru originally hails from Long Island, it is striking to think of the same place that used to be populated with Camaros and hair spray now blanketed with Wi-Fi. How times change!

It isn't exactly clear where you are accessing this hotspot from—you already receive Optimum broadband at home, but you're somewhere where you could theoretically set up a router to repeat the Optimum Wi-Fi signal. Office? Home of a friend with no other Internet access? Mother-in-law's? (In that case, spending your time on the street might actually be preferable.) Regardless, there are two options for solving the first part of your question—how to grab and repeat the Optimum Wi-Fi signal.

You will need a wireless router that supports DD-WRT, ideally the most current V24 release, such as the WRT54GL. You will need to flash DD-WRT onto this router.

You will need to decide whether to configure DD-WRT in either (a) wireless client mode, or (b) wireless repeater mode.

In wireless client mode, the router can pick up the wireless signal from the hotspot and relay it to devices connected by Ethernet to one of the router's LAN ports. (You can do this with wireless bridge mode, too, but when connecting to a public hotspot this may be less secure.)

In wireless repeater mode, the router picks up the wireless signal from the hotspot and re-broadcasts it locally. (DD-WRT V24 now supports repeater bridge mode, but again, bridging is less secure when connecting to a public hotspot.)

Of course, for either of these approaches to be useful, the router needs to be able to pick up the hotspot signal more successfully than your laptop does. This may well be the case out-of-the-box, or you may find it necessary to replace the router's stock antenna with a larger, more powerful substitute.

The second part of your question suggests that you'd like the router to maintain a permanent login to Optimum Online's hotspot gateway. Probably not. The Optimum Online hotspot requires re-authorization after two hours of use (or 20 minutes of idle time). Because these hotspots require authentication using a Web-based form, I don't know of any way to trigger the router to do this on your behalf. [For more on DD-WRT read our Compendium of DD-WRT.]

Q: I've taken your advice and I'm going to extend my network by running Ethernet to certain computers and the attic where I'll connect it to a Hi-Gain 7dBi antenna. My questions are:

1) I want to be able to upgrade to 802.11n for streaming HD content throughout the house wirelessly, hence the Hi-Gain antenna. However, most new routers have internal or non-detachable antennas--what to do?

2) With MIMO technology, should I have multiple Hi-Gain 7dBi antennas and mix omni vs. directional antennas for the best effect?

3) Should I use a directional antenna pointing down and hope it has a wide field to reach the corners of my house or an omni? – Dylan


A: I am touched when readers take my advice. This kind of thing warms a Guru's heart with the power of 200 milliwatts. But I have concerns. Let's step back for a minute and take a look at 802.11n networking.


Although the n standard has not yet been officially ratified, most major manufacturers are already releasing "pre-n" and "draft-n" devices based on the anticipated final 802.11n specification. Two of the most significant enhancements to 802.11n are both optional—support for the 5Ghz frequency and double-width (40Mhz) channels. When used in combination over a short range, 802.11n can achieve extremely high throughput rates for wireless, 150Mbps or more. But there are several real-world problems.


One, many draft-n routers do not yet have dual-mode radios—meaning that they operate only at the old 2.4Ghz frequency and don't support 5Ghz. Two, it is unusual to find a clean enough 2.4Ghz spectrum to allow for 40Mhz operation (for example, interference from other Wi-Fi networks or other 2.4Ghz devices), meaning that you will almost always need to be using the 5Ghz spectrum to support 40Mhz channels. Further complicating matters, range at 5Ghz is typically shorter than range at 2.4Ghz.


In other words, most off-the-shelf pre-n routers used in a typical real world environment won't be capable of achieving "maximum" speed. You can have maximum speed, or maximum range, but not both under the same conditions.


Streaming "HD" content raises another question. How much wireless bandwidth do you need to stream HD? At the risk of sounding Clintonian, that depends on what the definition of "HD" is. High-definition video can range widely in bitrate, from a few mbps to 20 or more mbps. There are variables of resolution, format, and encoding, for example. So it is difficult to say that you need x amount of bandwidth to stream all forms of HD video.


That said, playback of HD video can be resource-intensive, and small hiccups in transmission can quickly translate into interrupts and corruption in playback. Even if your wireless n network is fast enough for high-bitrate HD, playback can still be compromised by network events like links re-negotiation between router and client as conditions change.


To boil it all down, I have general concerns about relying on even an 802.11n wireless network to support all types of HD video streaming, and specific concerns about trying to beam that kind of bandwidth throughout a multi-story house using an antenna in the attic.


Because 802.11n is fastest at short range, I would advise re-configuring this plan. Put in the effort to run gigabit Ethernet cable to each level of the house, at least. If you need to stream HD to wireless clients, then consider an 802.11n router on each floor (or every other floor depending on building construction), so that your wireless clients can get the most benefit from n speed. Ideally, use 802.11n routers and clients that support 5Ghz operation so that you can enable 40Mhz channels and get the most wireless speed for your money.


Q: I tried this with WRT54G v8 and dd-wrt.v24_micro_generic.bin, but at step 4 I got (almost instantly) "Upgrade are failed!" (sic) in big red letters, then it returned to the firmware screen. It didn't brick my unit, it just looks like it rejected even trying to do the upgrade. – Danlip

A: A small wireless birdie tells me that you've already figured out the problem, but other readers may find it helpful to note that the WRT54G V8 is an oddball among the WRT54G series. You cannot simply flash it with DD-WRT firmware without first "killing" the proprietary OS—called VXWorks— loaded out of the box. Follow the directions here to download and flash the vxworkskiller, after which you can upload the feature-reduced micro version of DD-WRT onto this router (which has limited memory). Note that this procedure is better suited to the more advanced user compared to flashing a "normal" WRT54G. [For more on the WRT54G series of routers, read The Open Source WRT54G Story and How to Choose the Best WRT54G Router for You.]

Q: Does DD-WRT have a firmware upgrade for WRT160N-v2? I am trying to build a wireless bridge with the standard firmware. I have Router 1 connected and broadcasting, but I have been unsuccessful in bridging another WRT160N wirelessly. Can you help? – Steve

A: At this time there is not yet a DD-WRT version that supports the WRT160N-V2, although you can flash DD-WRT onto the original WRT160N. This is because the original flavor uses a Broadcom-based chipset, which is well supported by DD-WRT, but with the new V2 version Linksys has switched to a Ralink-based chipset. Rumor has it that some folks are working on porting DD-WRT to the V2, but it is not yet available and, to be realistic, may never be.

That said, why not simply reverse the two in your configuration? To build a wireless bridge, the key is running DD-WRT on the secondary (client) router. The primary (host) router does not need special firmware. Connect the V2 as your primary and configure DD-WRT on your V1 to bridge to it. [For more on DD-WRT bridges, click here.]

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.

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