Wireless Broadband in Allegany County
by Peter Gibson, Stratex Networks
Cahners In-Stat Group estimates that approximately 19 percent of U.S. households (180 million) are not served by DSL or cable. Some of these areas are so remote that it would cost millions to bring in the necessary fiber to serve them with broadband access. Others are in the midst of rough geographical terrain that also discourages incumbent service providers from building out broadband networks.
The network design for a rural community, (Allegany County, Maryland, USA), is one that can be used as a model for other rural counties worldwide. The idea for a wireless SONET solution came to the forefront. Using a combination of 311 Mbps licensed microwave equipment from Stratex Networks, 3 Mbps unlicensed microwave from Alvarion in the 2.4 GHz band, and 60 Mbps unlicensed microwave from Western Multiplex in the 5.7 GHz and 5.8 GHz bands, the county has been able to design a mature network called Allconet2. By combining a licensed microwave SONET backbone with an ATM sub-layer, Allegany County was able to inexpensively create carrier-class service.
Allegany County implemented a SONET ring in order to create a self-healing architecture. In the event of a radio link failure, automatic ring reversal occurs within 50 milliseconds. For the SONET backbone, AllCoNet chose Stratex Networks' Altium 311 radios and Fibrenex add drop multiplexers (ADMs). These wireless access products combine ultra-high capacity and high bandwidth efficiency into a single radio platform and provide information transport at 311 Mbps for simultaneous OC-3 and ATM transmission. Allegany County then added an ATM layer to the network to provide multi-ISP interoperability and ATM quality of service. Here, Stratex provided ATM switch equipment, sourcing the ASX-200BX ATM switches from Marconi.
Although there is a lot of current market interest in the new IEEE 802.11a &802.11b standards, AllCoNet 2 was built using other technologies. Residential access and small business access is provided by placing four multipoint transceivers operating at 2.4 GHz on each tower. The transceivers chosen for this implementation were not 802.11b but rather frequency hopping spread spectrum (FHSS) transceivers. FHSS provided better collocation and the ability to locate more than three 2.4 GHz transceivers per tower. High-bandwidth access for large businesses, enterprises, and ISPs is implemented by placing six multipoint transceivers that operate at 5.7 GHz on each tower. The transceivers chosen for this implementation layer were not 802.11a but rather TDMA transceivers. Access speeds can be scaled from 20 Mbps to 60 Mbps. More…
Reviewed January 2011
last updated : 21/01/2011
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