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Collision Avoidance: if another node was heard, we wait for a period of time (usually random) for the node to stop transmitting before listening again for a free communications channel. Request to Send/Clear to Send (RTS/CTS) may optionally be used at this point to mediate access to the shared medium. This goes some way to alleviating the ...
v. t. e. In IEEE 802 LAN/MAN standards, the medium access control ( MAC ), also called media access control, is the layer that controls the hardware responsible for interaction with the wired (electrical or optical) or wireless transmission medium. The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer.
In the Ethernet protocol, when a communication collision happens (when two users of the medium try to send at the same time), each user waits for a random period of time before re-accessing the link. However, a user will wait ("back off") for a random amount of time proportional to the number of times it has successively tried to access the link.
Carrier-sense multiple access. Carrier-sense multiple access ( CSMA) is a medium access control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus or a band of the electromagnetic spectrum . Under CSMA, a transmitter uses a carrier-sense mechanism ...
Distributed coordination function ( DCF) is the fundamental medium access control (MAC) technique of the IEEE 802.11 -based WLAN standard (including Wi-Fi ). DCF employs a carrier-sense multiple access with collision avoidance (CSMA/CA) with the binary exponential backoff algorithm. DCF requires a station wishing to transmit to listen for the ...
Orthogonality. Conceptually, OFDM is a specialized frequency-division multiplexing (FDM) method, with the additional constraint that all subcarrier signals within a communication channel are orthogonal to one another. In OFDM, the subcarrier frequencies are chosen so that the subcarriers are orthogonal to each other, meaning that crosstalk ...
Shannon's diagram of a general communications system, showing the process by which a message sent becomes the message received (possibly corrupted by noise) This work is known for introducing the concepts of channel capacity as well as the noisy channel coding theorem. Shannon's article laid out the basic elements of communication:
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