7. Wireless Ethernet Bridges

There are only so many ways you can combine the words "Ethernet", "Wireless", and "Bridge", and marketers have tried them all! But we're going to use the term "Wireless Ethernet Bridge" or "WEB" to differentiate the newest class of product from the AP/Bridges we've just described.

The most important thing you need to know about this class of devices is that they cannot act as an Access Point! This means that you can't set them to a mode where wireless clients that are set to Infrastructure mode will be able to associate, or connect, to them.

The other, more subtle, point to know is that although WEBs can be substituted for the AP/Bridges in any of the network configurations shown so far, they make their wireless connection in a different way than AP/Bridges do. WEBs make their Point-to-Point or Point-to-Multipoint bridges by using AdHoc mode instead of a special bridging mode. This use of AdHoc mode allows WEBs to do one thing that AP/Bridges can't do. Figure 4 tells the tale.

Figure 4: Wireless Network using AdHoc mode

If you compare Figure 4 with the previous illustrations, you'll see that by using WEBs instead of AP/Bridges, wireless clients can connect at both the local and remote ends of your bridge. But since everthing has to be set to AdHoc mode, there are some disadvantages:

Infrastructure mode clients will not be able to connect All stations must be set to the same ESSID and Channel

The first negative isn't a problem if you're running your own small network, because you can control the way that users configure their clients. But if you were setting up a "HotSpot" or wireless LAN (WLAN) intended to allow anyone to connect, you would pretty much have to stick to Infrastructure mode, because that's what WLAN clients will be set to.

The second negative is more of a deal-breaker for all except the smallest networks. Because all wireless clients must use the same channel, all clients will be sharing the same bandwidth. It won't take too many clients to bog down a WLAN, even if they're only moderately busy.

Note Figure 4 is somewhat misleading in that it implies that certain wireless stations are associating with certain other stations. In fact, a AdHoc station will connect directly to the station that it has traffic for.

Another advantage of WEBs over AP/Bridges is that when set to Infrastructure mode, they should be able to form a bridge to any 802.11b Access Point or wireless router, instead of only another copy of themselves. Of course, you may find that a particular combination of WEB and AP that doesn't work, but that would fall into the category of "bug" vs. "by design".