Everything you need to know about wireless bridging and repeating

Everything You Need To Know About Wireless Bridging & Repeating - Part 1: WDS DetailsTim Higgins28 June 2010
Introduction, WDS Explained, Interoperability Tips for WDS Success, Get MAC AddressEx. 1: Bridge w/WDS enabled routerTroubleshooting, Ex. 2: WDS bridge pairPerformance, Closing Thoughts

Many Wi-Fi routers come equipped with wireless repeating capabilities. But properly configuring them often isn"t easy. This article will Đánh Giá the basics of WDS-based wireless repeating & I"ll then walk through setting up a few examples.

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Please read references khổng lồ access points (AP) as applying lớn either access points or wireless routers unless otherwise noted.

WDS Explained

WDS, which stands for Wireless Distribution System, is a feature that enables single-radio APs to lớn be wirelessly inconnected 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 APhường STA (client) traffic. (In the 802.11 frame header, address 1 is the destination address, address 2 is the source address, address 3 is the BSSID of the network & address 4 is used for WDS, to indicate the transmitter address.)

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 lớn allow bridging features lớn 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 thiết kế originated by a long-defunct company called Choice Microsystems.

APs with wireless bridging features remained as high-priced items until fall 2002 when wireless bridging moved inkhổng lồ consumer priced wireless products. D-Link first broke the artificially high wireless bridging price barrier by releasing a không tính phí upgrade lớn its DWL-900AP+ Access Point . This upgrade created the first consumer-priced WLAN product khổng lồ tư vấn bridging & repeating. Other companies soon followed with similar upgrades, & also introduced dedicated Wireless Bridges, such as Linksys" WET11 <reviewed here>.

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Though these products were actually making use of the WDS feature, they didn"t refer lớn it as such. It wasn"t until products based on Broadcom"s 802.11g chipset started khổng lồ hit the market at the beginning of 2003 that the WDS term started khổng lồ be commonly used. (Broadcom apparently included WDS tư vấn in its APhường reference design code.)

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

Two disadvantages khổng lồ using WDS are:

It"s more difficult to phối up than non-WDS. Dynamically assigned and rotated encryption keys are not generally supported in a WDS connection. This means that Wi-Fi Protected Access (WPA / WPA2) & other dynamic key assignment technology might not be available. Static WEPhường keys are more commonly supported in WDS connections. Whatever encryption is supported in the WDS liên kết is what the repeater"s clients must use.

Note that wireless throughput is cut approximately in half for each repeating "hop", i.e. an APhường that data flows through before hitting the wired network. This is because all transmissions use the same channel & radio và must be retransmitted to reach the wired LAN. The repeating throughput reduction applies both khổng lồ WDS & non-WDS repeating.

WDS isn"t the only way lớn bridge & repeat, however. Some products don"t use WDS at all and instead act lượt thích wireless client adapters. But instead of connecting via USB, Cardbus or other computery interfaces, they connect via Ethernet. So they can be used khổng lồ wirelessly connect devices lượt thích media players, game systems or any other networkable device that has an Ethernet connector. I"ll cover these devices in another part of this series.

WDS Interoperability

As noted earlier, detailed specifications for WDS don"t exist. Instead, the wireless networking industry has been pursuing mesh wireless, which is self-configuring và self-healing. There is no mesh wireless standard yet—the IEEE Mesh Networking Task Group (TGs) has been grinding away since 2004 và isn"t scheduled khổng lồ be done until mid 2011.

In the meantime, companies lượt thích Meraki, Proxim, Cisco & others have sầu developed and sold wireless mesh systems.


Figure 1: Meraki mesh APs

These systems are intended for enterprise use và have sầu price tags to match. But if you"re interested in playing with the giải pháp công nghệ, inexpensive sầu 802.11g based mesh APs are available from Open-Mesh. Be warned, however, that throughput via 11g meshes is very low, in the single digit Mbps range. This is fine for basic connectivity for gmail, web browsing, etc. But not enough for high-chất lượng video clip streaming.

On a practical basis, however, consumers" main method for trying out wireless repeating are routers & APs with WDS built in. And with WDS added khổng lồ some 802.11n routers, it"s now possible khổng lồ get double-digit bandwidths through a single-hop bridge.

But WDS remains a technology, not a standard và WDS isn"t tested as part of Wi-Fi Certification. As a result, manufacturers typically include weasel-words somewhere in their sản phẩm documentation that say that bridging & repeating features will work only with their own products. And even if you don"t find WDS interoperability disclaimers, good luông xã trying to lớn get tư vấn from any vendor for a problem that involves any other vendor"s product!

The gist of all this is that products from different vendors with WDS bridging / repeating features are not guaranteed to work with each other! The industry has come a long way from the early days of WDS in terms of interoperability. But, again, there are no guarantees.