Although this unit doesn't stack up all that well against the competition, we're not sure we really played to Young Design's strength. The company offers a much broader array of products that operate in the 2.4-GHz band as well as a number of helpful RF utilities and some of the best technical information available on any vendor Web site.
Model EX-1, starts at $8,000 ($8,500 as tested), Young Design, (888) 297-9090, (800) 664-7060, (703) 205-0600. www.ydi.com
Dave Molta is a Network Computing senior technology editor. He is also an assistant professor in the School of Information Studies and director of the Center for Emerging Network Technologies at Syracuse University in New York. Write to him at [email protected]. Cornell W. Robinson III is a research associate at the Center for Emerging Network Technologies and a freelance reviewer. His experience includes four years in IT and a position as network manager of Point Park College in Pittsburgh. Write to him at [email protected].
We tested the fixed wireless point-to-point systems in our Syracuse University labs using calibrated radio-frequency attenuators to simulate the free space path loss that would occur in a typical outdoor installation. Although our test bed let us simulate longer links, our objective was to simulate a 1-mile connection. At 5.3 GHz, the path loss for a 1-mile link is approximately 111 dB. Because some of the products include integrated antennas and others work with a variety of external antennas, we controlled for the effects of antenna gain by assuming that each product used an antenna on each end with a gain of 23 dBi, a number typical of several commercially available directional path antennas. We also corrected for path loss in our cabling system. For the products that included integrated antennas, we requested vendors provide an RF connector that bypassed the internal antenna.
Because an antenna on each end would provide 46 dBi of total signal gain and our expected 1-mile path loss is 111 dB, we expected each product to operate properly with 65 dB of attenuation (111 minus 46). All the products met that standard. We also measured the level of attenuation at which each product stopped operating and compared that result to what we would expect based on manufacturers' claims of radio output power and receive sensitivity. We found that all the products operated within 5 percent of these specifications. Thus, we're confident in stating that, when properly installed with appropriate antennas, all these products will operate at the distances stated by the manufacturers.
For performance testing, we used NetIQ Chariot's filercvl TCP test using 100 iterations of 1-MB records to evaluate the maximum throughput under optimal conditions. The test bed consisted of four 1.2-GHz Toshiba Satellite notebook computers with 256 MB of RAM running Microsoft Windows XP. All computers and wireless bridges were connected to a Cisco 3500 switch with VLANs defined for each bridge and its computer pair (see diagram). We measured peak and average performance in unidirectional half-duplex mode and average aggregate performance in bidirectional full-duplex mode. We also ran the same tests with the notebook computers connected directly to the switches to establish a baseline Ethernet measurement and ensure that the notebook computers themselves were not a bottleneck. The range of microwave systems is limited by a number of technical radio characteristics as well as by the curvature of the earth. Most high-performance systems require direct line of sight between antennas. Because designers must take into account the RF effects of a system's Fresnel zone (the pattern of electromagnetic radiation that is created by a transmitting station from its antenna to receiving antennas), bridges should be elevated sufficiently off the ground to ensure reliable operation.
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