metropolitan area network (MAN)
Metropolitan Area Networks (MAN) are city networks or regional networks whose characteristic features position them between local area networks( LAN) and wide area networks(WAN). MANs are networks with a regional footprint designed for a wide variety of transmission services, such as voice, data, moving images, and so on.
In addition to the classic services, city network operators can offer value-added services in the voice area and in the data area. In the voice area, these include: the Centrex service, least cost routing and computer telephony integration; in the data area, communication via the Internet or via company intranets, the formation of virtual networks and e-commerce.
The concept of city networks
City networks cover communication needs within cities and metropolitan areas in a more elegant and powerful way than is possible with wide-area networks. City networks are based on Synchronous Digital Hierarchy( SDH), a technology for logically interconnecting cables and establishing logical links between subscribers. Since SDH hierarchy is only a technology for providingcables and logical connections, and not a mediating technology, a mediating technology such as ATM must be used in the case of a service offering. The use of 10 Gigabit Ethernet( 10GbE) is also under discussion.
The expansion of city networks
The extent for a city network is 100 km or more, and the transmission speed is 100 Mbit/s to 1,000 Mbit/s. MANs use optical fiber as the transmission medium to realize the high transmission speeds with the lowest possible error rate.
InIEEE, city networks are standardized in 802.6. In terms of topology, this is a double bus, consisting of two unidirectional buses running in opposite directions. All stations in such a network are connected to both buses. Data traffic can run full- duplex in either direction, with one or the other bus being selected for transmission depending on the destination address. Thanks to this topology, various network concepts can be implemented: Point-to-point connections, bus top ologies or a looped bus, i.e. logical ring topologies on a physical bus.
As an access method, MANs according to 802.6 use the Distributed Queue Dual Bus( DQDB) method, which is equally suitable for packet-oriented asynchronous data traffic and for isochronous transmissions. Since there are no length restrictions for Gigabit Ethernet and 10 Gigabit Ethernet, city networks are increasingly being designed as transmission networks for Ethernet services. These Ethernet city networks are called Metro Ethernet Networks( MEN).