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To access the contents, click the chapter and section titles.
Wireless Networking Handbook
Spread spectrum resists interference from traditional narrow band radio systems, enabling systems using both modulation techniques to exist in the same space. The only signals that are likely to cause serious interference originate from other spread spectrum devices. The disadvantage, then, is the possible interference with others operating similar wireless MANs nearby. With wireless LANs, interference is normally not a problem because the radio waves are kept indoors, within the confines and management of the organization. Radio waves traveling between buildings, perhaps across a large city, will be beyond the organizations jurisdiction and control, possibly receiving interference from other unknown systems. The owning organizations and users of the wireless MAN equipment, therefore, will probably not be able to do anything about the interference. Many companies sell spread spectrum wireless MANs. The following are examples of spread spectrum-based wireless MAN products: Proxim's RangeLINKProxims RangeLINK family of high speed wireless bridges connects LANs in buildings separated by up to three miles. RangeLINK operates in the 2.4 GHz band at 1.6Mbps using frequency-hopping spread-spectrum technology. The RangeLINK Series 1500 is for multipoint solutions and enables you to have a central bridge (RangeLINK 1510) that connects multiple remote facilities within a range of one mile from the central site. Each remote facility must use a RangeLINK 1520 or 1530. The RangeLINK Series 2000 is for high-speed, longer-distance (up to three miles) solutions. Persoft's Intersect Remote BridgePersofts Intersect Remote Bridge uses spread spectrum radio frequency operating with the 902 MHz and 2.4 GHz ISM bands to filter packets between points at two locations. The Intersect Remote Bridge has a data transmission rate of 2.0 Mbps with a maximum range of five miles. This product can interface with either ethernet or token ring LANs. Solectek's AIRLANSolectek has a product, the AIRLAN Bridge Plus, which operates in the 902 MHz ISM frequency band and delivers data at 2 Mbps. AIRLAN provides connectivity between ethernets located up to three miles apart. Solecteks AIRLAN/Router 200 routes Internet Protocol (IP) and Internetwork Packet Exchange (IPX) packets within MAN environments. AIRLAN/Router 200 combines multiprotocol routing with wireless bridging to provide an internetworking solution at 2 Mbps for LANs up to 25 miles apart. The AIRLAN/Router 200 software, co-developed by Cisco Systems, increases network availability and performance by providing broadcast control, protocol mediation, and network security using optional DES encryption. The AIRLAN/Router 200 utilizes spread spectrum radio in the 2.4 GHz ISM band. The AIRLAN/Router 200T is compatible with IEEE 802.5 Token Ring, and the AIRLAN/Router 200E is compatible with IEEE 802.3 Ethernet. Antennas mount on the roof of the building and require a line-of-sight path to the destination. Cylink's AirLink BridgeCylinks AirLink Bridge functions as a remote ethernet bridge that filters packets at full, wired ethernet speed and forwards only the appropriate packets across wireless links up to 20 miles long. In addition, the link is full-duplex, so there are no end-to-end collisions that degrade throughput and cause re-transmission. The AirLink bridge uses direct sequence spread spectrum radios tuned to 2.4 GHz. LANNAIR's EthAirBridgeLANNAIR produces a wireless bridge called EthAirBridge, which interfaces Ethernets over a range of 15 miles. It operates in the 2.4 GHz ISM band and delivers data at 76.8 Kbps. An optional 4:1 data compression board increases performance to 307.2 Kbps. In addition, an RS-232/V.24 or V.35 interface is available that can support a dial-up back-up link. The RS-232 interface supports data rates from 4.8 to 19.2 Kbps, and the V.35 interface supports data rates up to 2.048 Mbps. Windata's AirPortWindata, Inc. makes a system called AirPort, which operates at 5.7 Mbps data throughput. AirPort reaches this relatively high speed by separating the send and receive channels onto different radio bands and using error correction. The AirPort I system has a range of 1,000 feet, and AirPort II can send signals within a 0.9 mile radius. SpreadNet's Wireless LinkSpreadNets product, Wireless Link, provides throughput up to 2 Mbps. The Wireless Link product is available in configurations that support transmission distances of short range (5 miles), medium range (625 miles), and long range (70 miles using repeaters). Narrow Band Wireless MANThe FCC and comparable regulatory agencies in other countries regulate the use of narrow band frequencies. This regulation offers both an advantage and disadvantage. The FCC licenses each user site to operate on an assigned frequency, often a 25 KHz slice of bandwidth, which gives the user specific rights for operating on the assigned frequency at a specific location. If interference occurs, for example, the FCC will intervene and issue an order for the interfering source to cease operations. This is especially advantageous when operating wireless MANs in areas having a great deal of operating radio-based systems. The disadvantage is that the licensing process can take two or three months to complete. You must complete an application, usually with the help of a frequency consultant, and submit it to the FCC for approval. Thus, you cant be in a hurry to establish the wireless links. Plus, you will probably have to coordinate with the FCC when making changes to the wireless MAN topology. Multipoint Networks sells one of the very few wireless MAN products that operates on narrow band frequencies. Multipoint produces both point-to-point and point-to-multipoint narrow band wireless MAN systems. All Multipoint products operate within the 400-512 MHz and 820-960 MHz frequencies and have a range of 30 miles or more. The point-to-point product, called Radio Area Network (RAN), operates in full-duplex mode ranging in data rates from 9.6 to 125 Kbps. The main applications of RAN are for the replacement of leased lines and wireline modems within metropolitan areas.
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