How to Reanimate Dead Spots in Wi-Fi Networks - Page 2

By Gerry Blackwell

July 07, 2011

We look at various options to remedy localized Wi-Fi network outages.

Invest in a Wi-Fi Site Survey

To conduct a site survey, a consultant sets up an AP in the environment and connects to it using a laptop computer running special mapping software, preloaded with a plan of the facility.

He then moves around the building, using the software to map coverage characteristics -- where signals are weaker, where they’re stronger.

“What you end up with is like a heat map, showing maybe green for good [connectivity], yellow for borderline, red for poor, for every place in the office,” Sharony says.

The best of this type of software is smart enough to automatically calculate the number of access points needed to cover a facility or floor and make recommendations for their optimal placement.

Sharony’s firm uses Site Survey software from Ekahau, a Finnish firm. It’s a product designed for network professionals and costs about $5,000, he says. Another comparable product often used by pros is AirMagnet Survey from Fluke Networks.

But Ekahau also has a less capable freeware version called Heat Mapper. There are other freeware, evaluation and inexpensive site survey products, including VisiWave Site Survey SO from AZO Technologies and Covera Zone from Celtrio.

If you conduct a site survey and discover you need more than one AP to eliminate all potential dead spots, there are a few possible ways to deploy and configure them. In enterprise networks, each AP is typically connected to an Ethernet "backbone" that connects them to the Internet.

More and more new homes today are wired with Ethernet in every room, so it may be possible to design a network in a large new home the same way. But in most homes and many small offices, running Ethernet to all APs will be difficult or impossible.

In that event, you will have to either resort to some of the Band-Aid solutions mentioned earlier or install multiple APs capable of working in "bridge" or "repeater" mode -- in effect creating a wireless backbone. This is also referred to as a Wireless Distribution System (WDS).

One router or AP, connected to the Internet, functions as the root, while others, configured in bridge mode and located nearer the dead spots, connect wirelessly to the root, and at the same time, provide wireless connectivity to nearby client devices.

Even if you assume you’ll only need one AP and don’t want to go to the trouble or expense of conducting a site survey, it makes sense to select a router or AP that can support bridge mode. Most enterprise products do, but only newer and higher-end SOHO products do.

If you start with a SOHO device that cannot support bridge mode and later discover you need additional APs, you will have to abandon the first product and start over (or use Band-Aid solutions).

Also be aware that for all practical purposes you will have to standardize on one vendor’s products and possibly one model, because bridge-mode functionality typically uses proprietary protocols and will not work between products from different vendors, or sometimes even between different models from the same vendor.

Some APs can only function in point-to-point bridge mode, meaning they can only connect wirelessly to one other AP. Some support point-to-multipoint mode, connecting in bridge mode to multiple other APs.

With products supporting point-to-multipoint bridging, mostly enterprise products, you can create a wireless mesh, making it even easier to eliminate dead spots caused by transient multipath effects. Mesh networks have many potential routes for sending traffic and can pick the route with the best throughput at any given moment.

Linksys, Cisco’s consumer brand, does not include WDS functionality in its router products on the assumption that it’s not required in a residence. It’s Cisco-branded small business routers do have this feature.

Netgear says all of its current consumer and SOHO grade routers support repeater mode or WDS in both point-to-point and point-to-multi-point modes.

Coverage holes or dead spots are an almost inevitable problem with even the simplest Wi-Fi networks. They can be filled in, however. The best approach is a site survey and a network designed to eliminate dead spots at the outset.

In the absence of a site survey, if you’re lucky, you can eliminate dead spots with minimal expense and effort -- but count on having to install additional infrastructure.

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