Access Technologies in Software

Generator Code39 in Software Access Technologies

A number of fixed broadband wireless technologies have emerged that present a potential alternative to traditional wired access infrastructures. These include Local Multipoint Distribution Service (LMDS), Multichannel Multipoint Distribution Service (MMDS), 802.11 (Wi-Fi), and Freespace Optics.

Local Multipoint Distribution Service (LMDS)

LMDS is a bottleneck resolution technology, designed to alleviate the transmission restriction that occurs between high-speed LANs and wide area networks (WANs). Today, local networks routinely operate at speeds of 100 Mbps (Fast Ethernet), 1,000 Mbps (Gigabit Ethernet), and even 10 Gbps, which means that any local loop solution that operates slower than any of those poses a restrictive barrier to the overall performance of the system. LMDS offers a good alternative to wired options. Originally offered as CellularVision, it was seen by its inventor, Bernard Bossard, as a way to provide cellular television as an alternative to cable. It is, in effect, wireless DSL. Operating in the 28 GHz range, LMDS offers data rates as high as 155 Mbps, the equivalent of SONET OC-3c. Because it is a wireless solution, it requires minimal infrastructure and can be deployed quickly and cost effectively as an alternative to the wired infrastructure provided by incumbent service providers. After all, the highest cost component when building networks is not the distribution facility, but rather the labor required to trench it into the ground or build aerial facilities. Thus, any access alternative that minimizes the cost of labor will garner significant attention. LMDS relies on a cellular-like deployment strategy under which the cells are approximately three miles in diameter. Unlike cellular service, however, users are stationary. Consequently there is no need for LMDS cells to support roaming. Antenna/transceiver units are generally placed on rooftops as they need unobstructed line of sight to operate properly. In fact, this is one of the disadvantages of LMDS (and a number of other

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wireless technologies): Besides suffering from unexpected physical obstructions, the service suffers from rain fade caused by absorption and scattering of the transmitted microwave signal because of atmospheric moisture. Even some forms of foliage will cause interference for LMDS, so the transmission and reception equipment must be mounted high enough to avoid such obstacles hence the tendency to mount the equipment on rooftops. Because of its high bandwidth, many LMDS implementations interface directly with an ATM backbone to take advantage of ATM s bandwidth and its diverse quality of service capability. If ATM is indeed the transport fabric of choice, then the LMDS service becomes a broadband access alternative to a network capable of transporting a full range of services including voice, video, image, and data the full suite of multimedia applications.

Even with the gloomy forecasts coming from the dark corners of the telecommunications industry, there is hope for broadband wireless solutions such as LMDS. Three key applications for LMDS have emerged in markets where the technology has been deployed: voice, remote LAN access, and interconnection and interactive television. These three applications alone make LMDS a powerful contender in the broadband access market. Of course, fixed wireless has been hit hard, as have other segments of the telecom space. The three major suppliers Advanced Radio Telecom, Winstar, and Teligent filed for bankruptcy. All three took on enormous debt to build their networks quickly, but when the markets began to disappear in late 2000, they were left with few customers. Most of their assets have been picked up by carriers, especially long-distance carriers looking for a viable entry technology for the local loop market. Many left the market over security and reliability concerns associated with wireless. Nevertheless, industry analysts predict that fixed wireless is real, will survive the turbulent market, and will see revenues exceed $14 billion by 2006. In fact, other technologies such as WiMAX (described later in this chapter) may provide viable alternatives.

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