Wireless Distribution System
From Wikipedia, the free encyclopedia
A Wireless Distribution System is a system that enables the interconnection of access points wirelessly. As described in IEEE 802.11, it allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. [1]
An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay main station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between "clients" are made using MAC addresses rather than by specifying IP assignments.
All base stations in a Wireless Distribution System must be configured to use the same radio channel, and share WEP keys if they are used. They can be configured to different service set identifiers.
WDS may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). It should be noted, however, that throughput in this method is inversely proportional to the number of "hops", as all traffic uses the same channel. For example, client traffic going through one relay station before it reaches the main access point will see at most half the maximum throughput that a directly connected client would experience.
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[edit] Implementations
WDS may be incompatible between different products (even occasionally from the same vendor) as it is not certified by the Wi-Fi Alliance.
- The WRT54GL from Linksys is able to make use of the Wireless Distribution System via a 3rd party firmware like DD-WRT, Openwrt, or Sveasoft.
- Apple's Airport Extreme and Airport Express are both able to use WDS. Also, the majority of Buffalo routers support WDS.
- All NETGEAR ProSafe access points (WG102, WAG102, WG302, WAG302) natively support the full implementation of the Wireless Distribution System. Several of their SOHO devices do also, whether with full implementations like the WG602v2/v3 or partial implementations like the WPN802.
- All USRobotics MAXg wireless products (5451, 5461, 9108, 5432, 5441) support WDS.
Note: a Wireless Distribution System is distinct from the WDS implementation by Cisco, which stands for Wireless Domain Services.
[edit] Technical
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 usually not supported in a WDS connection. This means that Wi-Fi Protected Access (WPA) and other dynamic key assignment technology in most cases can not be used. This is due to the lack of regulation in this field, which will hopefully be resolved with the upcoming 802.11s standard. As a result only static WEP keys may be used in a WDS connection, including any STAs that associate to a WDS repeating AP.
