High Toll for Wireless Bridge

Cisco's Aironet 1400 offers great functionality, but for a price.

July 22, 2003

4 Min Read
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The 1400 utilizes an integrated antenna/radio combination. In contrast to Cisco's first-generation BR-350 bridge, the Aironet 1400's integrated design provides a greater RF link budget because the radio signal is completely contained within the outdoor unit, eliminating the need for costly high-grade shielded outdoor cabling. The radio unit has two

F-type coaxial connectors, four weather-shielded LED indicators and a BNC jack for measuring RSSI (receive signal strength indicator) power measurements. In addition, the 1400 includes a power-injecting Ethernet switch transceiver, which converts 100-Mbps Ethernet and 48-volt DC power into a signal carried on dual coaxial RG-6U conductors.

The power injector unit is a separate, indoor enclosure that has an integrated Ethernet-to-Ethernet bridge, letting customers deploy the wireless solution up to 600 feet from the wiring closet--300 feet from the wiring closet to the bridge, and another 300 feet from the indoor bridge to the outdoor antenna. The unit also functions as a tranceiver, converting standard Ethernet and power into a signal that travels over dual coax conductors. Although proprietary, dual coax conductors are easier to ground than Category 5 Ethernet, and they're also more moisture- and weather-resistant.

Putting It to the Test

I installed and roughly aligned the first antenna, then mounted the second bridge at a remote site. When I powered the first bridge up, it went into root-bridge mode after 60 seconds. Once the second bridge powered up, it contacted the root bridge and linked instantly. The bridge ships from the factory in this "install" mode, but if you want to configure bridge parameters manually (to adjust transmit power, distance vector or IP address, for instance), you need only plug in an Ethernet cable and the bridge will autonegotiate a link and provide a DHCP address to your client.

AiroNet 1400click to enlarge

I installed the 1400 on the rooftop of Preston Wireless, 0.6 miles from its primary PoP (point of presence), located at the top of a 150-foot grain tower in downtown Green Bay. A voltmeter confirmed an RSSI voltage of 1.38 volts on both ends of the link. Higher voltages are directly proportional to higher receive-signal strength. My initial performance tests yielded poor results, so I used the Web-based configuration GUI to lower the bridge transmit power, which was too high for the range of our initial test.

Using Ganymede Chariot 4.3 and a pair of high performance workstations, I benchmarked the solution at 27.6 Mbps for half-duplex throughput and 30.7 Mbps for full-duplex throughput, near the theoretical maximum data rate for 802.11a based hardware. Ping tests indicated latency of less than 1 millisecond.

I then moved the home office radio to a remote PoP 5.5 miles away and realigned the antennas, measuring an RSSI voltage of 1.19 volts. At 5.5 miles, the 1400 achieved 19.9 Mbps of throughput in unidirectional tests, and 20.6 Mbps in bidirectional tests.

Aironet Specs

The 1400 operates using 802.11a technology in the UNII-3 band (5,725 MHz to 5,825 MHz), providing four 20-MHz wide nonoverlapping channels for use in North America.The radio and software are engineered with draft support for the 802.11e wireless QoS (quality of service) standard. Packets can be queued and prioritized according to their Layer 2 or Layer 3 QoS tags, or via their virtual LAN ID. Cisco says the device can support up to 24 simultaneous VoIP (voice over IP) sessions with QoS.

The bridge radio supports a maximum of 24 dBm (250 mW) transmit power and its receive sensitivity is -68 dBm at 54 Mbps.

Cisco provides a wealth of security and authentication features with the included IOS software, including multilevel console user access control, RADIUS and TACACS+ authentication of users to the console, and the option to use RADIUS and 802.1X to authenticate remote bridges and provide advanced encryption and security from a central site.Broad Range, High Price

Cisco's solution combines strong performance, ease of setup, and a hardware bundle that gives you everything you need to get up and running, but the device is costly. At $4,999 for each integrated antenna bridge, the 1400 is double the price of competing devices--such as Proxim's QuickBridge 20--and wireless VARs can construct FCC-certified 802.11a-based bridging solutions for even less. The Aironet 1400's key values lie in its potential range and its IOS operating system, which provides significantly greater functionality and manageability than many devices on the market.

Joel Conover, a former senior technology editor of Network Computing, is a principal analyst at tactical competitive response solutions firm Current Analysis. Write to him at [email protected].

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