Metro Area Networks (MANs)

Metro Area Networks (MANs)
The WMAN encompasses a range of radio- and laser-based technologies targeted at providing wireless
networking over distances of a few hundred meters to several miles. Wireless broadband, broadband
wireless access (BWA), wireless local loop (WLL), fixed wireless, and wireless cable all refer to
technologies that can be used to deliver telecommunications services over the last few miles of the
network. Wireless broadband and BWA are general terms referring to highspeed wireless networking
systems. WLL is derived from the wired telephony term local loop, which refers to the connection
between a local telephone switch and a subscriber. WLL and fixed wireless generally refer to the delivery
of voice and data services between fixed locations over a high-speed wireless medium. Some new
market entrants offer mobile applications of this technology. Fixed wireless includes Local Multipoint
Distribution Service (LMDS), Multichannel Multipoint Distribution Service (MMDS), Unlicensed National
Information Infrastructure (U-NII) systems, and similar networks. Wireless cable usually refers to MMDS
systems used to deliver television signals such as the Instructional Television Fixed Service (ITFS).
Two basic network topologies are supported by these systems. The simplest is a point-to-point system
providing a high-speed wireless connection between two fixed locations. Bandwidth is not shared, but
links typically require line of sight between the two antennas. The second topology is a point-to-multipoint
network where a signal is broadcast over an area (called a cell) and communicates with fixed subscriber
antennas in the cell. Because bandwidth in the cell is finite and is shared among all users, performance
may be a concern in high-density cells. Systems of different frequencies may be combined to cover an
area where terrain or other obstructions prevent full coverage.
Other than frequency, the main difference between fixed wireless systems, and cellular, WLAN, and
WPAN networks is the mobility of subscriber equipment. There has been some discussion about adding
support for mobile subscriber equipment to fixed wireless systems. The addition of mobility support would
enable these BWA systems to potentially function as fourth-generation (4G) cellular networks, delivering
subscriber speeds of several megabits. Several technical, regulatory, and commercial hurdles must still
be overcome before this could become a reality, but companies such as Wi-Fi have already started
examining products targeted at this potential application.[