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Wired for wireless

The cabling requirements for wireless access need to be taken into account during the planning stage of any new building construction.

November 1, 2005  

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I was searching for a theme for this month’s article on cabling standards, and came up with a topic that looks fundamentally like a contradiction in terms — wired for wireless. This is not just a play in words. This is serious business. A task group under TIA TR 42 Technical Committee is nearing completion on a new document that will soon be published as TIA TSB-162 “Telecommunications Cabling Guidelines for Wireless Access Points”.

At our last meeting in October, this document was tentatively approved for publication pending agreement on the resolution of ballots.

The cabling requirements for wireless access need to be taken into account during the planning stage of new building construction.

Cabling for wireless access is in addition to the traditional cabling requirements specified in ANSI/TIA 568-B.1 standard. TSB-162 provides guidelines for pre-cabling a building using a grid approach. The pre-cabled grid makes the building ready for a wireless infrastructure at any time simply by plugging in a wireless access point.

Let’s start with the basics. A grid is a collection of uniform cells where each cell is a square.

A convenient size for a square cell is 60-feet-by-60-feet (18.3 m by 18.3m), which is based on the typical coverage area of currently available wireless access points and on the typical bay size for commercial buildings in North America.

The size of the cell and the number of required wireless access points per cell will depend on the coverage, bandwidth, types of applications, quality of service and the number of users.

The wireless outlet (for lack of a better word) is located in the center of the square cell, either above or below the drop ceiling.

This allows the capability to move the access point anywhere within the square using a patch cord that is up to 0.707 X in length, where X is the size of the square. For X equals to 60 feet, the maximum length of patch cord is 42 feet or 13 meters.

For this configuration, the length of horizontal cable is limited to 80 meters. The recommended cabling is Category 5e or higher. Two-fiber multimode optical fiber cable may also be installed.

Different mounting arrangements for the wireless access points are described. These include Wall-mount above drop ceiling, Wall-mount below drop ceiling and In-the-grid ceiling mount. Some of these options are more aesthetically pleasing than others.

It is recommended that power be delivered through the horizontal cabling utilizing IEEE 802.3af compliant equipment at both ends. This eliminates the need to install a local power outlet within the vicinity of the wireless access point.

Most wireless access points have an attached or built-in antenna. Some wireless access points also have the option to attach remote antennas that are mounted externally to the device.

These antennas are attached to the wireless access point via coaxial cabling and can provide extended coverage for hard to reach areas or better coverage in one direction (also known as directional antennas).

The use of an external antenna can provide greater flexibility in locating, concealing and mounting the wireless access point.

Today, wireless access is becoming more and more prevalent in business, education and healthcare environments. The recently published IEEE 802.11g standard for wireless local area networks (WLANs) offers transmission over relatively short distances at a theoretical maximum of 54 megabits per second (Mb/s).

A study conducted by Intersil indicated that the effective data throughput in an indoor office environment is about 20 – 22 Mb/s for distances of 50 to 60 feet, 15 to 20 Mb/s for distances of 60 to 70 feet, 10 – 15 Mb/s for distances of 70 to 80 feet and 5 – 10 Mb/s for distances of 80 to 120 feet. These ranges are consistent with the recommended cell size in TSB-162.

Are you ready for wireless? Above all, a wireless LAN requires a wired infrastructure to support wireless access. It is a lot easier, more flexible and less costly to provision for a wireless infrastructure during the initial building construction rather than as an afterthought.

The convenience and versatility of plug and play wireless cannot be underestimated.

Paul Kish is Director, Systems & Standards at Belden CDT. He is also vice chair of the TR-42 engineering committee.

Disclaimer: The information presented is the author’s view and is not official TIA correspondence.