The foregoing observations led to the development of carrier sense multipleaccess (CSMA). With CSMA, a station wishing to transmit first listens to themedium to determine if another transmission is in progress (carrier sense). If themedium is in use, the station must wait. If the medium is idle, the station may transmit. It may happen that two or more stations attempt to transmit at about the sametime. If this happens, there will be a collision; the data from both transmissions willbe garbled and not received successfully. To account for this, a station waits a reasonable amount of time after transmitting for an acknowledgment, taking intoaccount the maximum round-trip propagation delay and the fact that the acknowledging station must also contend for the channel to respond. If there is no acknowledgment, the station assumes that a collision has occurred and retransmits.
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