One possible way around the problem of the limited spectrum available for wireless LANs is to use infrared light as the transmission medium. There are both direct infrared systems(range: 1-3 mi)and nondirect systems bounced off walls or ceilings). For small areas data rates are consistent with those of existing ethernet and token ring networks with 100-Mb/s systems on the horizon Asyncronous Transfer Mode (ATM) LANs2 ATM LANs are relatively new to the Lan marketplace. This is a packet switching technology utilizing relatively short, fixed length packets to provide networking services. ATM was originally seen as a way to develop the next generation wide area telephone network using packet switching, rather than the more conventional circuit itching technology. It was envisioned as a way to transport video, voice, and data in an integrated network a short packet size was chosen to meet several requirements including minimizing real-time queueing delay While progress on the original goal of using aTm technology in wide area telephone networks proceeded slowly because of the complexity of the challenge and the large investments involved, a number of smaller companies introduced ATM local area network products using much the same technology An ATM lAn consists of a switch into which are wired end users in a star-type topology. There are several possibilities for the internal architecture of the switch. A low-cost switch may essentially be a computer bus in a box. More sophisticated switches may use switching fabrics. These are very large-scale integrated (VLSI implementations of patterned networks of simple switching elements, sometimes referred to as space division switching. A great deal of effort has gone into producing cost-effective ATM switches over the past 12 years. It should be pointed out that many of the issues that are not yet resolved for wide area network ATM (i.e, traffic policing, billing)are more tractable in the private ATM LAN environment. ATM LANs can support a relatively small number of users at high data access rates(low megabit per second) Although ATM is good at handling mixed media traffic at high speeds, it remains to be seen if enougH applications are developed requiring its high-bandwidth capability to make it a success. The cost effectiveness of ATM technology is another issue awaiting resolution Private branch exchange Historically, private branch exchanges(PBXs) were privately owned telephone switching computers that would be placed in the basement of a building and serve to interconnect phones in the building and provide access to outside lines provided by common carriers. However, PBXs are now available that offer both telephone and data service. In a typical system a phone may have a data socket for terminals or workstations. PBXs are wired in a star topology with the PBX at the center of the star and each user wired directly to it. 92.3 Metropolitan Area Networks While several network architectures have been proposed for use as MANs, the two that are closest to widespread commercial implementation are fiber-distributed data interface(FDDI) and distributed queue dual bus (DQDB)interface. A key feature of a MAN is the ability to interconnect LANs. This is a problem because of the high data rates at which LANs operate FDDI The FDDI is similar to a token ring lan except that two rings, instead of one, may be used. Stations needing high-reliability communication are connected to both rings. In the case of a break in the rings the network can e automatically reconfigured. FDDI rings operate at 100 Mbps with a maximum of 500 nodes and a maximum fiber length of 200 km. In fact, most actual FDDI installations have only a small number of nodes(such as routers). There is an American National Standards Institute(ANSI)standard for FDDI. This material was previously published in The Mobile Communications Handbook, J D. Gibson, Ed, Boca Raton, Fla. CRC Press. 1996 e 2000 by CRC Press LLC© 2000 by CRC Press LLC One possible way around the problem of the limited spectrum available for wireless LANs is to use infrared light as the transmission medium. There are both direct infrared systems (range: 1–3 mi) and nondirect systems (bounced off walls or ceilings). For small areas data rates are consistent with those of existing ethernet and token ring networks with 100-Mb/s systems on the horizon. Asyncronous Transfer Mode (ATM) LANs2 ATM LANs are relatively new to the LAN marketplace. This is a packet switching technology utilizing relatively short, fixed length packets to provide networking services. ATM was originally seen as a way to develop the next generation wide area telephone network using packet switching, rather than the more conventional circuit switching technology. It was envisioned as a way to transport video, voice, and data in an integrated network. A short packet size was chosen to meet several requirements including minimizing real-time queueing delay. While progress on the original goal of using ATM technology in wide area telephone networks proceeded slowly because of the complexity of the challenge and the large investments involved, a number of smaller companies introduced ATM local area network products using much the same technology. An ATM LAN consists of a switch into which are wired end users in a star-type topology. There are several possibilities for the internal architecture of the switch. A low-cost switch may essentially be a computer bus in a box. More sophisticated switches may use switching fabrics. These are very large-scale integrated (VLSI) implementations of patterned networks of simple switching elements, sometimes referred to as space division switching. A great deal of effort has gone into producing cost-effective ATM switches over the past 12 years. It should be pointed out that many of the issues that are not yet resolved for wide area network ATM (i.e., traffic policing, billing) are more tractable in the private ATM LAN environment. ATM LANs can support a relatively small number of users at high data access rates (low megabit per second). Although ATM is good at handling mixed media traffic at high speeds, it remains to be seen if enough applications are developed requiring its high-bandwidth capability to make it a success. The cost effectiveness of ATM technology is another issue awaiting resolution. Private Branch Exchange Historically, private branch exchanges (PBXs) were privately owned telephone switching computers that would be placed in the basement of a building and serve to interconnect phones in the building and provide access to outside lines provided by common carriers. However, PBXs are now available that offer both telephone and data service. In a typical system a phone may have a data socket for terminals or workstations. PBXs are wired in a star topology with the PBX at the center of the star and each user wired directly to it. 92.3 Metropolitan Area Networks While several network architectures have been proposed for use as MANs, the two that are closest to widespread commercial implementation are fiber-distributed data interface (FDDI) and distributed queue dual bus (DQDB) interface. A key feature of a MAN is the ability to interconnect LANs. This is a problem because of the high data rates at which LANs operate. FDDI The FDDI is similar to a token ring LAN except that two rings, instead of one, may be used. Stations needing high-reliability communication are connected to both rings. In the case of a break in the rings the network can be automatically reconfigured. FDDI rings operate at 100 Mbps with a maximum of 500 nodes and a maximum fiber length of 200 km. In fact, most actual FDDI installations have only a small number of nodes (such as routers). There is an American National Standards Institute (ANSI) standard for FDDI. 2 This material was previously published in The Mobile Communications Handbook, J. D. Gibson, Ed., Boca Raton, Fla.: CRC Press, 1996