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Metropolitan Area Network
Metropolitan area networks, or MANs, are large computer networks usually spanning a city. The MAN is typically a backbone optical network that spans a metropolitan area, usually in a ring configuration. The MAN is designed to cover a metropolitan area or campus and provide network access throughout the area. Many college campus networks would be classified as a MAN because they have multiple buildings spread out geographically, sometimes throughout the community.
By the size a MAN is larger than a local area network (LAN) which would typically be found in a corporate office or at home. But MAN is also smaller than a Wide Area Network (WAN), which is a network that stretches long distances, often between multiple business sites within different communities.
The telephone companies have provided MAN services in the form of SONET rings for years. These services are based on TDM (time division multiplexing), which is more suitable for voice than data. Customers connect into the ring via ISDN, T1, fractional T1, and even T3 lines. However, even for short distances, these connections are expensive.
MAN networks use a different standard for communications. Standard 802.6 assigned by the Institute of Electrical and Electronics Engineers (IEEE), which uses a different bus technology to transmit and receive data than the larger or smaller networks.
Because of the huge growth of wireless technology and the increases in the number of Internet and network users, the use of MAN networks will likely continue to grow well into the future. Someday perhaps there will be a network that extends from coast to coast which may, if all connected to the same network, be considered a metropolitan area network.
Implementation of MAN
Some technologies used for this purpose are ATM, FDDI, and SMDS. These older technologies are in the process of being displaced by Ethernet-based MANs (e.g. Metro Ethernet) in most areas. MAN links between LANs have been built without cables using microwave, radio, or infra-red laser links. Most companies rent or lease circuits from common carriers due to the fact that laying long stretches of cable can be expensive.
DQDB, Distributed Queue Dual Bus, is the Metropolitan Area Network standard for data communication. It is specified in the IEEE 802.6 standard. Using DQDB, networks can be up to 20 miles (30 km) long and operate at speeds of 34 to 155 Mbit/s.
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