WDS Explained

WDS stands for Wireless Distribution System and is a feature supported by an increasing number of 802.11 access points. Simply put, it enables single-radio APs to be wirelessly connected instead of using a wired Ethernet connection.

WDS connections are MAC address-based and employ a special Data Frame type that uses all four of the (MAC) address fields allowed in the 802.11 standard, instead of the three addresses used in normal AP <-> STA traffic.

The provision for four MAC addresses in a frame is about the only thing covered by the 802.11 standards, but it was enough to allow bridging features to first be added to enterprise-grade, i.e. expensive, 802.11b products in the late 1990's. Many of these implementations were based around a medium access control (MAC) layer design originated by a company called Choice Microsystems.

APs with wireless bridging features remained as high-priced items until fall 2002 when wireless bridging moved into consumer priced wireless products. D-Link first broke the artificially high wireless bridging price barrier by releasing a free upgrade to its DWL-900AP+ Access Point. This upgrade created the first consumer-priced WLAN product to support bridging and repeating (see below). Other companies soon followed with similar upgrades, and also introduced dedicated Wireless Bridges, such as Linksys' WET11 [reviewed here].

Though these products were actually making use of the WDS feature, they didn't refer to it as such. It wasn't until products based on Broadcom's 802.11g chipset started to hit the market at the beginning of 2003 that the WDS term started to be commonly used. Broadcom apparently included WDS support in its AP reference design code and WDS-enabled 802.11g APs have since become more widely available.

WDS can be used to provide two modes of wireless AP-to-AP connectivity:

• Wireless Bridging in which WDS APs communicate only with each other and don't allow wireless clients or Stations (STA) to access them

• Wireless Repeating in which APs communicate with each other and with wireless STAs

Two disadvantages to using WDS are:

• Wireless throughput is cut approximately in half for each WDS repeating "hop", i.e. an AP that data flows through before hitting the wired network. This is because all transmissions use the same channel and radio and must be retransmitted to reach the wired LAN.

• Dynamically assigned and rotated encryption keys are not supported in a WDS connection. This means that Wi-Fi Protected Access (WPA) and other dynamic key assignment technology may not be used. Static WEP keys only may be used in a WDS connection, including any STAs that associate to a WDS repeating AP.

Tags: Bridging, How To, WDS, WiFi,

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