Nonbroadcast multiple-access network
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A Nonbroadcast Multiple Access Network (NBMA) is a network to which multiple computers and devices are attached, but data is transmitted directly from one computer to another over a virtual circuit or across a switched fabric. NBMA does not support multicast or broadcast traffic. Some common examples of nonbroadcast network media include ATM, Frame Relay, and X.25.
Other examples of non-broadcast multiple access media are wired networks that operate over power lines. Due to strong Multipath propagation, power lines create frequency-selective channels. Channel frequency response is different for each pair of (transmitter/receiver), so modulation parameters (for example, the actual bit-loading in each OFDM subcarrier) are unique for each pair of (transmitter/receiver).
The fact that each pair of devices uses a different modulation scheme for communication means that other devices may not be able to demodulate the information sent between them. For this reason, power lines are considered a Nonbroadcast multiple-access network. The ITU-T G.hn standard, which provides a way to create a high-speed (up to 1 Gigabit/s) Local area network using existing home wiring (power lines, phone lines and coaxial cables), is an example of a technology capable of operating over Nonbroadcast multiple-access network.
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