CSE 123 Lecture Notes - Lecture 26: Carrier-Sense Multiple Access, Media Access Control, Frequency-Division Multiple Access
5 Dec 2018
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Document Summary
Bridges - different than what we know about bridges! We learned that bridges were store-and-forward devices that speak the same layer. These bridges are not ethernet cable to cable. Runs a different media access control (mac) Synch, gain setting, energy detection, frequency offset compensation. Hec (header error check) - protection of signal, service & length. | synchronization | sfd | signal | service | length | hec | payload. 12 channels available for use in the us. Fdma - 100 mhz divided into 3 separate channels. Persistent csma: retry immediately w/ probability p. B can hear both a and c, but a and c cannot hear each other! Problem: when a transmits to b, c cannot detect the transmission using the carrier sense mechanism. If c transmits, collision will occur at node b. Wireless mac protocols often use collision avoidance techniques in conjunction w/ a (physical or virtual) carrier sense mechanism.
