Metropolitan Area Networks:-
Metropolitan Area Network, or Man (plural: MANs, not MEN) is basically a bigger version of a
LAN and normally uses similar technology. It might cover a group of nearby corporate offices or a
city and might be either private or public.A MAN can support both data and voice, and might even
be related to the local cable television network. A MAN just has one or two cables and does not
contain switching elements, which shunt packets over one of several potential output lines. Not
having to switch simplifies the design.
The main reason for even distinguishing MANs as a special category is that a standard has been
adopted for them, and this standard is now being implemented. It is called DQDB (Distributed
Queue Dual Bus) or for people who prefer numbers to letters, 802.6 (the number of the IEEE
standard that defines it). DQDB consists and two unidirectional buses (cables) to which all the
computers are connected, as shown in Second Figure. Each bus has a head-end, a device that
initiates transmission activity. traffic that is destined for a computer to the right of the sender uses
the upper bus. Traffic to the left uses the lower one.
A key aspect of a MAN is that there is a broadcast medium (for 802.6, two cables) two which all
the computers are attached. This greatly simplifies the design compared to other kinds of
networks. we will discuss DQDB in more detail in chap.
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