Don't Let 802.11b Bring You Down

By Ronald Pacchiano

October 28, 2005

Buying an 802.11g router won't improve your wireless LAN's performance if you also have 802.11b devices connected to it. The good news is that there is a painless resolution to ensure that slower Wi-Fi devices don't slow down the faster ones.

I have a considerable amount of money invested in 802.11b products — multiple PC card adapters, some USB adapters and even a wireless print server. Recently, I purchased a new notebook equipped with an 802.11g wireless adapter. It worked fine on my network, but I figured since I had the "g" adapter already, I might as well take advantage of the extra speed its capable of by upgrading my router to a wireless "g" model. So I purchased a new D-Link "g" router (only $20 bucks after rebates) and installed it on my network. I configured it to support both "b" and "g" devices and everything works fine.

Here's my concern. The other day I was speaking with a business associate, and he said that because I'm running both "b" and "g" devices on the same network, I'm not really getting the full performance of the "g" adapter. He went on to say that my network's "b" adapters might not even be performing as well as they had before the router upgrade due to the mixed environment. So I spent all that money on a new "g" notebook and router just to get slower performance? This can't be right.

He said the only way to get the network to perform at the higher speed would be to upgrade all the devices to the "g" standard. As I said, I have a lot of 802.11b devices, and I hate the thought of having to replace all of them. If what he said is true, are there any other options available to me?

Well, I have good news and bad news for you.

The bad news is that what he told you is 100 percent true. It has long been acknowledged that mixed-mode wireless networks — those that simultaneously run clients with both 802.11b and the five times faster 802.11g, which operate in the 2.4GHz radio band — can suffer speed wise. Specifically, using the slower 802.11b can drag down throughput on an 11g network.

802.11g clients are rated to run at 54Mbps, though they usually get only around 20 to 25 Mbps in real world use. 802.11b clients are rated for 11Mbps, but top out at around 6Mbps. The farther away the devices are from an access point, the lower the throughput drops.

However, if both "b" and "g" products are operating on the same router or access point, the speed can drop much more dramatically. In fact, in a report conducted by the Tolly Group of Boca Raton, Fla., indications are the situation is actually much worse than what was previously suspected.

In a series of tests conducted with off-the-shelf enterprise class access points and up to four concurrently running client systems in various configurations — everything from a full-speed 11g notebook down to a PDA running 802.11b at only 1 Megabit per second (Mbps) — revealed that just one client running at an extremely reduced data rate can bring all the clients down significantly. As a result, any wireless devices running at a higher speed is going to be impacted by a slower device on the same channel.

Think of it like two people moving through the Lincoln Tunnel. One person can walk through the tunnel at one mile per hour, while another drives through at 50 mph. The problem is that if I'm walking ahead of you, you have to wait. The faster device is still capable of the higher speed, but it's stuck in a queue behind the slower one.

The good news, though, is that there is another option available to you. You can take your "g" router back to the store and swap it for a "g" access point. Connect the new "g" access point to your old "b" based router. By adding the access point to your wireless router you've basically created two wireless LANs (WLANs) on your network — one "b" and one "g."

Next configure the "b" WLAN for "B Only" access and the "g" access point for "G Only" access, thereby ensuring that the proper adapter connects to the appropriate network. Now you'll need to set a channel for each WLAN to broadcast on. The 2.4GHz band supports up to three non-overlapping channels. These are channels one, six and 11. Have each WLAN broadcast on a separate, non-overlapping channel. By using the non-overlapping channels, you essentially isolate each WLAN, minimizing the chances of interference and thus giving you the best performance.

For maximum efficiency, you should also check to see if your neighbors on either side of you are running a WLAN. You wouldn't want your "b" network to be on the same channel as your neighbors. If they use channel six for "b," you'd want channel one for "b" and channel 11 for "g." That way they all avoid each other interference-wise. (The 802.11b laptop is probably still going to pick whatever network has the faster signal, though — yours or the neighbor's — unless you limit it to using your specific SSID network name.)

Best of all, since the router is still managing the network (IP address assignments, workgroup and so), systems on both WLANs should be able to communicate with each other with no problem. So you'll still be able to share files and print to the wireless print server.

Adapted from PracticallyNetworked.com, part of the EarthWeb.com Network.

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