Understanding Wireless Bridging
and the Wireless Distribution System (WDS)
Connect802 can help with the selection and system design for many manufacturer's Wi-Fi Wireless Mesh Router and Bridging equipment. We understand Mesh Router technology, point-to-point and point-to-multipoint wireless bridging and we know how to build a system that will meet your requirements.
If you have questions, please don't hesitate to call us today! We'll be happy to provide you with any technical explanation that you need to help you assure a successful wireless networking deployment.
A wireless bridge provides a relatively straightforward point-to-point or point-to-multipoint wireless Ethernet connection. A Wireless Distribution System (WDS) is a system of two or more wireless bridges built using 802.11 access points. Bridging fundamentally involves manual configuration of the end-points and assumes that the topology will remain static (as opposed to Mesh Routing which is fundamentally dynamic in both configuration and topology).
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The 802.11 standard doesn't specifically define a "bridge" so we fall back on the industry-accepted definition of a bridges as a device that connects two portions of the same network using the same, or different Data Link Layer protocol (i.e.: 802.11 Wi-Fi and 802.3 Ethernet). In the realm of bridging as a general technology the term "learning bridge" refers to a bridge that keeps track of where frames came from so it knows how to intelligently forward frames back only onto the port out which the intended destination can be reached. In the case of most wireless LAN bridging, and always in the case of the Wireless Distribution System, there is no learning. All packets received on by the wireless bridge are forwarded to either one destination, or to a group of destinations. In every case, however, the destination is the same for all packets forwarded by the wireless LAN bridge. This, of course, is not a limitation of any kind when viewed in the context of the most common implementation of WDS - the point-to-point bridge link between two buildings.
Why Is It Called A Wireless "Distribution System"?
The term "distribution system" refers to the 802.11 standard's definition of the infrastructure that connects Access Points to each other. A group of Access Points are configured with the same network name (SSID) and create a single, distributed wireless LAN. Since these Access Points form a single logical network they must exist in a single Layer 2 broadcast domain. When any station sends a broadcast it must go to all other stations in the LAN. Consequently, all the Access Points forming a single WLAN must be connected to each other in some manner. Normally this is through an Ethernet switch. In that case the term is "wired distribution system." Alternatively, radio links can interconnect Access Points. In this case it's referred to as a "wireless distribution system" or "WDS". The simplest wireless distribution system consists of two Access Points. If these Access Points are not providing client association services then they operate just as if their sole purpose was to bridge between two portions of a wired Ethernet. Hence, wireless LAN bridging is also called a Wireless Distribution System.
The Basic Components of a WDS Point-to-Point Link
802.11 Access Points Operating In WDS Mode
A pair of Access Points are configured to forward traffic to each other. This creates a Wireless Distribution System and results in wireless LAN bridging between the two Ethernets "behind" the Access Points.
High-Gain Directional Antennas To Create Point-to-Point Links
Adding a high-gain, directional antenna allows up to one mile using conventional Wi-Fi equipment with line-of-sight connectivity across a wireless LAN bridge link in a Wireless Distribution System.
Definitions and descriptions of Wireless Bridging and WDS that you might find on the Web:
A Bridge is a device that allows wired LANs to interconnect with other wired LANs. Wireless Bridges allow same building or multi-building connectivity without the use of hardwire. Bridges work at OSI model Layer 2 and forward data depending on destination hardware addresses (MAC). Only data with valid destination addresses are sent across a bridge.
Wireless networking offers a cost-effective solution to users with difficult physical installations such as campuses, hospitals or businesses with more than one location in immediate proximity but separated by public thoroughfare. This type of installation requires two access points. Each access point acts as a bridge or router connecting its own LAN to the wireless connection. The wireless connection allows the two access points to communicate with each other, and therefore interconnect the two LAN's.
Segmenting a large network with an interconnect device has numerous benefits. Among these are reduced collisions (in an Ethernet network), contained bandwidth utilization, and the ability to filter out unwanted packets. However, if the addition of the interconnect device required extensive reconfiguration of stations, the benefits of the device would swiftly be outweighed by the administrative overhead required to keep the network running. Bridges were created to allow network administrators to segment their networks transparently. This means is that individual stations need not know whether there is a bridge separating them or not. It is up to the bridge to make sure that packets get properly forwarded to their destinations. This is the fundamental principle underlying all bridging behaviors.
Wireless Distribution System is a system that enables the interconnection of access points wirelessly. 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. All base stations in a Wireless Distribution System must be configured to use the same radio channel, and share WEP keys if that is used. They can be configured to different SSIDs .
In IEEE 802.11 terminology a "Distribution System" is system that Interconnects, so-called, Basic Service Sets (BSS). A BSS is best compared to a"Cell", driven by a single Access Point. So a "Distribution System" connects cells in order to build a premise wide network which allows users of mobile equipment to roam and stay connected to the available network resources. A distribution system can be Wired (typically Ethernet), or Wireless (using the radio device inside the Access Point).
WDS (Wireless Distribution System) is a Wireless Access Point mode that enables wireless bridging in which WDS APs communicate only with each other only (without allowing for wireless clients or stations to access them), and/or wireless repeating in which APs communicate both with each other and with wireless stations (at the expense of half the throughput).