Home: www.packetnexus.com
http://www.networkcomputing.com/1019/1019f3.html Wireless T1 WANs Make Waves September 20, 1999 By Dave Molta and Asad Irshad Your mission: Establish a reliable WAN able to carry voice and data without using dedicated circuits or requiring FCC approval. Impossible? Take a look at unlicensed radio-based T1 wireless local loops. For a onetime equipment and installation fee, you can avoid recurring charges for T1 lines, which can top $1,000 per month for a local loop, and cost much more than that when the connections cross LATA (local access transport area) boundaries. Perhaps more important than these savings, wireless T1 loops can provide flexibility in areas where the cabling infrastructure to support dedicated lines is lacking, as is often the case in rural communities, for example. For years, microwave towers have dotted the landscape, but these systems are usually very expensive and require FCC licenses. Technological advances and government policy have spawned an alternative--unlicensed spread-spectrum radio systems operating at 2.4 GHz and 5.8 GHz. Many products are now available, including a number of 10-Mbps and 100-Mbps offerings designed primarily to interconnect Ethernet LANs. Although it's tough to beat T1 products when your needs include both voice and data, T1 tends to cost a lot more than 10-Mbps bridges. If your needs call exclusively for LAN connectivity, bridges make more sense. In Network Computing's Real-World LabsŪ at Syracuse University, we put five wireless T1 products--Adtran Tracer, BreezeCom BreezeLink, Glenayre Western Multiplex (GWM) Lynx.sc, P-Com AirPro T1/E1 and Wave Wireless Speedcom T1/E1-- through a series of tests to assess their suitability for transporting both voice and data across metropolitan area networks. Lynx.sc edged out P-Com AirPro T1 and Adtran Tracer for our Editor's Choice award; it was easy to install and performed flawlessly. GWM also provides the broadest line of single and multichannel T1 products at both 2.4 GHz and 5.8 GHz. In addition, AirPro earned our Best Value award. Besides the fact its $6,995 retail price was almost the lowest among the products we tested, P-Com is running a promotion through the end of 1999 offering a pair of radios, antennas and cabling for $6,995. That's value. We tested the wireless devices in a hybrid voice-data network, passing data among Cisco routers and voice traffic across Nortel Meridian PBXes (see "How We Tested,"). All the products got the job done, though only the Lynx.sc provided 100 percent of the baseline throughput we were able to achieve with a hardwired connection between the ADC/Kentrox CSU/ DSUs we used on our test bed. Tracer fell just shy of 100 percent, while AirPro and Speedcom were also very close, achieving throughputs in excess of 98 percent. BreezeCom's BreezeLink did not fare quite so well. On the PBX side, all the products delivered clear voice communication. Installing these products is not a job for amateurs (see "Installation Issues," page 90). Aiming antennas, particularly across distances of 20 miles or more, isn't easy; make sure that you install lightning arrestors and follow other safety precautions. Selecting the proper cables, antennas and output signal level requires knowledge of RF transmission characteristics, as well as the impact of weather conditions. With the exception of BreezeLink, all the products claim to support links of 10 miles or more with 99.999 percent availability (5.25 minutes of expected o