Networking / Beginners

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Bridging Wireless Networks Together

Sometimes you want to establish a multi-access point wireless network in your home or office, but you don't have Ethernet cabling running to the locations where you want to add the extra AP. After all, you may be using wireless because you don't have wires in place already.

One way to overcome this problem is to use a system built into some brands of wireless APs and wireless routers that is known as Wireless Distribution System (WDS).

WDS basically creates a mesh network by providing a mechanism for access points to "talk" to each other as well as sending data to devices associated with them.

Remember WDS is based on some standardized 802.11 protocols, but there is no standardized way of implementing it that works across different AP and router vendors. So if you have a D-Link AP in one location and you want to create a WDS link to a ZyXEL router in another location (just to pick two brands at random), you probably won't be able to get it to work. You have your best luck when you use equipment from the same manufacturer.

Warning Some equipment that supports WDS does not support advanced security systems like WPA or WPA-Enterprise on a WDS network - only WEP. Think long and hard about your choice to use WDS in these cases - WEP is secure enough to keep your friends out, but should be considered essentially insecure if you've got anything that's seriously worth protecting on your network.

Remember When you use WDS as a repeater system, as described below, it effectively halves the data rate for clients connected to your APs. That's because every bit of data needs to be sent twice (data is received by the AP and then retransmitted).

To configure WDS, you need to modify some settings on each AP within the network. Your exact steps (and the verbiage used) will vary from vendor to vendor. Generally, you'll see some settings like the following:

• Main WDS station: One of your WDS stations is the main base station for the WDS network. This AP is connected directly to your Internet connection, or connected to your router via a wired connection. The main station is the bridge to your Internet connection that all wireless traffic eventually flows through.
• Repeater WDS stations: In a simple, two-AP WDS network, the other "unwired" AP is a repeater. The repeater receives data from the main base station and relays the data to the wireless clients associated to the repeater station (and vice versa for data coming from the clients). If you have more than two APs, remote APs may be repeaters, or they may be relays that provide an intermediate stopping point for data if the repeater is too far away from the main station to communicate.

When you configure your main or base WDS station, take note of the channel you're set to and the ESSID or network name of your network. If your AP has any kind of channel auto configuration function that changes channels based on network conditions, be sure to disable this feature. If your main WDS station is also your network's router, make sure it's set up to distribute IP addresses in the network.

Tip Write down or otherwise take note of the MAC addresses of all of your WDS stations - many configuration software systems require you to know these addresses to make the configuration settings work. Write down the wireless MAC address (it's often on a sticker) and not the Ethernet MAC address.

Turn on the WDS functionality in your main station (it's often labeled WDS, or may say something like Enable This Base Station As a WDS Main Base Station - that's the wording Apple uses for their AirPort Extreme products). When you turn on this functionality, the configuration software may ask you to identify the remote repeater(s). Have the MAC addresses of those repeaters handy in case you need them.

Depending upon how your software works, you may have to separately access the configuration software on the remote repeater APs to turn on WDS. Here are a few things to remember:

• You need to assign any other WDS stations to the same channel that your main base station is using. This is counterintuitive to many folks who have had the 802.11b/g "use channels 1, 6, and 11 and keep your APs on different channels" mantra driven into their heads for a long time!
• You set the ESSID of the remote location(s) using either a unique name or by using the same ESSID as you use for your main base station. (Whoa, our heads just exploded!) Using the same ESSID (a "roaming" network) is pretty cool. You associate with one AP one time and then your PC or Mac can associate with any AP on your WDS network without you having to do anything - it's more seamless this way. But remember, you don't have to do this - you can give each AP a unique ESSID and just configure your computer to associate with them according to your preference.
• Make sure you turn off any routing or DHCP functionality in the remote repeater stations. All of this functionality should be performed in the main base station or the network's main router.

Remember We're discussing WDS in a repeater mode where the remote APs provide wireless access to PCs and other wireless clients.

Tip If you have Linksys wireless routers (or one of a few other supported brands), you can check out the Sveasoft firmware (www.sveasoft.com). This software replaces your AP's existing software load and provides mechanisms for creating mesh networks that work in a way similar to WDS. You can get mesh without having to spend extra money on an AP that supports WDS.

Tip If you need to create a big mesh network with multiple APs to cover some serious ground, check out the gear sold by Tropos Networks (www.tropos. com). Their equipment includes its own specialized operating system that controls the flow of traffic between and among access points - providing a specialized "mesh" traffic management system. These systems are used by many cities and municipalities when they create regional "hot zones" serving dozens of square miles of territory.