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	F E A T U R E

Wireless T1 WANs Make Waves September 20, 1999 P-Com AirPro T1/E1 P-Com offers a range of licensed and unlicensed radio products offering performance through DS-3. The AirPro T1/E1 is a relatively new product that came to the company via its acquisition of Cylink Corp.'s Wireless Communications Group. P-Com is also an OEM provider to a number of vendors, including Wave Wireless, whose Speedcom E1/ T1 we also tested. The AirPro has a single-unit design. We evaluated the rack-mount version, but a ruggedized version suitable for outdoor installations is also available. The modular units offered by Wave Wireless and Adtran supply power over the coax cable that interconnects the modem and RF units. If you install a ruggedized P-Com AirPro on an antenna mast, you will need to provide a separate DC power source. In most cases, users will probably choose the rack-mount unit. Like the Wave Wireless and BreezeCom offerings, the AirPro is configurable via a terminal interface. Our initial attempts to set up the AirPro were thwarted by miswired DB-9 to RJ-45 adapters supplied by P-Com. The vendor assured us that it has cleared the defective adapters from its inventory. The configuration and management interface is command-oriented, and though it includes useful features such as context-sensitive help and automatic keyword completion, we found it more difficult to use than Tracer's menu interface, which provides dynamic updates of operational performance indicators. The AirPro provides an extensive set of alarms with definable thresholds. You can also configure the unit to dial out automatically through the serial port to report alarm logs. Unlike Speedcom T1/E1, Tracer and Lynx.sc, which all operate in true full-duplex mode using separate transmit and receive frequency bands (20 MHz per channel for Speedcom T1/E1 and Lynx.sc, 40 MHz for Tracer's dual T1), the AirPro is built around a time-division duplex (TDD) design. Using a guassian frequency shift keying (GFSK) modulation scheme and a single 95-MHz channel, the AirPro simulates full-duplex operation by doubling the normal T1 transmission rate and buffering data on both ends of the connection. This sleight of hand is largely transparent to applications, but it introduces a slight delay of just under three milliseconds, which is acceptable for mainstream data and voice applications. In our data testing, we noted a very slight performance differential between the AirPro and offerings from GWM and Adtran. Also unique to the AirPro is its support for burst synchronization, which is designed to improve performance at hub-site installations where potential interference between multiple radios can limit the number of links coming into a single site. By interconnecting all radios using twisted-pair bus, transmissions are synchronized to eliminate interference. Like Lynx.sc, the AirPro provides an order-wire interface that allows ordinary analog phone sets to communicate across the wireless link. We liked the placement of the order-wire jack, which is conveniently available on the front panel of the unit next to the terminal jack. Order-wire and terminal interfaces are available on the rear of the unit. We also liked the fact that front-panel LEDs are duplicated on the back of the unit to aid in configuration and troubleshooting. AirPro T1/E1, $6,995, P-Com, (800) 646-7266, Ext. 4246, (408) 866-3666; fax (408) 866-3566. www.p-com.com
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