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Wireless Bridging Example

One of the most obvious advantages of wireless networking is the absence of cables and this advantage is most apparent when there is a need to link two or more locations, whether it may be connecting your attic to your basement or two offices several kilometres apart. This kind of connection is usually done using WDS (Wireless Distribution System) between wireless access points and/or routers. It is important when selecting devices to use for your bridge to ensure that they support WDS.

To determine whether or not a wireless bridge is suitable for your needs the main factor that must be addressed is signal quality. The ideal bridge would be a short distance link with no obstacles in the path of the signal (such as walls). Most devices use the common 2.4ghz or 5.8ghz frequencies and neither are tolerant to objects in the path of the signal, with the strength of the signal reduced with everything that it has to pass through. Some materials or very thick objects will completely block the signal. The best links have a completely clear path between access points, which is referred to as "line of sight" or LOS. 2.4ghz is by far the most widely used frequency and is much more tolerant of non line of sight situations than 5.8ghz. And yes, a window will reduce the strength of the signal.

For a short link, say from attic to basement the antenna that ships with the devices you intend to use for creating the wireless bridge will be fine as long as care is taken to ensure that the path between the devices is as clear as it can be. Some devices work quite effectively up to 500m with a clear signal path using their standard stubby six inch antenna's. External antenna's mounted on a buildings roof can extend the range of an access point quite markedly, I have built links that join two locations over 20km apart however at that range true line of sight and high gain directional antenna's are necessary.

When configuring your wireless bridge there are three things that must be absolutely identical for each device used in the bridge, the SSID, the channel and the security settings. Unfortunately WPA ecryption cannot be used by WDS so 128 bit WEP encryption is the next best choice. The WDS example that we have chosen creates a bridge between a Billion Bipac 7300G and a Netgear WG602, which we have documented elsewhere as our Wireless ADSL Modem Configuration Example and our Access Point Configuration Example. Both of these devices have been configured as documented with the following points-

  • They use the same SSID and channel
  • They have the same level of WEP encryption and identical WEP keys
  • Their LAN IP addresses are on the same network

Billion BIPAC 7300G WDS Setup - Click to enlargeFor WDS to work the MAC (Media Access Control) address of each participating device must be entered into the other devices configuration for it to be aware of it and attempt to connect to it. A MAC address is a unique hexadecimal address that is built into a device upon its manufacture and we would really be muddying the waters to explain it further than that. Suffice it to say that it is highly unlikely that you will have two devices with the same MAC address and the MAC address cannot be easily changed on most devices. Our Bipac wireless adsl modem displays its MAC address in the Configuration >> LAN menu and our example modems address is 00:19:DB:0B:DA:35 which must be entered into the configuration of the Netgear WG602 that it will connect to for the bridge to work. To enable WDS on the Bipac modem simply select enable on WDS service. There is provision to enter in up to four MAC addresses of devices to bridge to and we can see in our example that the MAC address of the Netgear is already typed in. We would simply click apply then save config, saving the settings to flash so that they are still there when the modem is restarted and the Bipac is configured ready to be used.

Netgear WG602 WDS Setup - Click to enlargeThe Netgear WG602 is configured in a similar fashion on the Wireless Bridging link of its configuration page but the Netgear can be more extensively tailored to suit your needs than the Bipac modem. It has the option of access point mode, which is the default setting. Wireless point to point bridging does basic WDS to join to points together and ticking Enable Wireless Client Association allows other computers and devices to connect as well. Wireless multi point bridging allows more than one WDS connection to allow multiple locations to connect. Repeater with wireless client association allows wireless clients to connect and sends data immediately to the remote wds device. Client mode allows a desktop PC, printer or other device without a wireless adaptor of its own to connect to a remote access point. In our example we have selected Wireless Point to Point Bridging to create a link to our Bipac ADSL modem. We have ticked Enable Wireless Client Assocation to allow PC's, laptops etc to connect to the netgear and use it to get internet access from our ADSL modem. The remote MAC address entered is of course the ADSL modems MAC address. Dont forget to click apply. Readers actually using a WG602 will find its MAC address on its information page, the first page you see when you log into the access point. On the bottom of the bridging page the Netgear displays a list of associated clients and signal strengths. We can see our Bipac Billion 7300g associated and the bridge should be working just fine. We have left the DHCP server enabled on the Bipac and it should assign an address to any client connecting at either end of the bridge.

HINT if you have configured both devices of a bridge and they are connected via ethernet in some way your whole network may stop working. That is because they are connected in more than one way, creating two paths or a loop to all of your ethernet traffic. Unplug one of them from the network and this effect will go away in a few seconds.

 

 

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