Buyers Guide

There's Relief Ahead For Your Wireless Woes

In addition to radio-based systems, infrared wireless systems also are available, operating at very high frequencies, just below visible light in the electromagnetic spectrum. Directed infrared often is used for point-to-point links that can be configured and tuned to deal with the directional characteristics of these signals. Diffuse infrared is used on some LAN-based products, but its inability to penetrate opaque objects, such as walls, limit it to individual rooms. Infrared works very well as a wireless conference room or classroom solution.

Implementation and Management Issues Implementing a w ireless LAN is more difficult than would be the case for a traditional wired LAN, but it may be a little easier than you might expect. For a building-to-building wireless li nk, the two major variables to consider are the distance of the connection and the speed required for the link. A high-speed link of 10 Mbps or more generally has required, until recently, the services of an external vendor to install the system, perform a preliminary site analysis and to assist with FCC license acquisition. For a lower-end spread-spectrum link that does not require FCC license, you may find that you can perform the installation yourself. A short-distance connection of up to 1,000 feet often can be handled without the need to mount antennas on a building. Rather, you may be able to use inexpensive omnidirectional antennas pointed out a window or perhaps a small YAGI-style antenna mounted in an attic. Most products include software to aid in the aiming of antennas, which assures optimal signal transmission.

For installations that require the mounting of an antenna outside the building, some expertise is required to ensure that the system is properly mounted and that appropriate measures are taken to install lightning arrestor equipment. Location of the bridge-router equipment can be tricky, since there are distance limitations of the cabling that runs between the radio and the antenna. The choice of antenna will depend on the distance of your link. Most vendors will provide an antenna that will be suitable for a one to three mile transmission distance. Keep in mind, however, that higher-gain antennas are available at reasonable prices.

For intrabuilding wireless LANs, it's a little more complex. In small buildings or larger buildings that lack obstructions, a single access point may be all that is needed to provide appropriate geographic coverage. In larger facilities, and particularly those with large amounts of metal or concrete, you will need to divide the building into cells, similar to those used by cellular phone syst ems. Although this is conceptually straightforward, it can require significant expertise to optimize the number and location of access points. Most vendors are able to pr ovide general guidance at no charge or more advanced technical services for a fee.

Today's products have improved significantly with respect to ease of configuration and management. Look for a product that provides flexible configuration capabilities. The ideal product lets you configure it in-band via some kind of configuration utility or telnet session, or out-of-band via a console port. Simple Network Management Protocol (SNMP) agents are found on most systems, but the sophistication of the information reported varies considerably. Nearly all will support basic Management Information Base (MIB) I and MIB II, but enterprise extensions are needed to let you monitor parameters such as signal strength and packet loss on the wireless connection. You also should investigate software updates. Some systems load their software from a floppy disk, while others use firmware. The latter is generally preferred as more reliable, if updating is easy.

One final bit of advice is a holdover from the days when prestand ard 10BASE-T Ethernet products were offered. Many organizations found it desirable to specify requirements for free upgrades to standards-compliant systems as insurance against potential changes between the draft and final 10BASE-T standards. Organizations contemplating the acquisition of products compliant with 802.11 draft standards should look for the same kind of protection from their vendors.

Dave Molta is director of network and system services at Syracuse University. He can be reached at dmolta@nwc.com.

Wireless LAN Alliance Touts Its Image

According to Jeff Abramowitz, WLANA's president, response to the group's initial education efforts have been positive. "We've been very pleased with the feedback we've received so far. The thousands of hits we receive on our Web site every week are an indication of the growing interest in Wireless LANs," he notes. WLANA's Web site, www.wlana.com, includes basic tutorial information related to wireless LANs, case studies of successful wireless LAN implementations, links to WLANA member sites and links to sites dealing with wireless LAN technologies.