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Apple's LocalTalk implemented CSMA/CA on an electrical bus using a three-byte jamming signal. 802.11 RTS/CTS implements virtual carrier sensing using short request to send and clear to send messages for WLANs (802.11 mainly relies on physical carrier sensing though). IEEE 802.15.4 (Wireless PAN) uses CSMA/CA
IEEE 802.11 RTS/CTS (request to send/clear to send) is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem. Originally the protocol fixed the exposed node problem as well, but later RTS/CTS does not, but includes ACKs.
Thus RS-232's use of the RTS and CTS signals, per the older versions of the standard, is asymmetric. This scheme is also employed in present-day RS-232 to RS-485 converters. RS-485 is a multiple-access bus on which only one device can transmit at a time, a concept that is not provided for in RS-232.
Request to send and clear to send, flow control signals RS-232 RTS/CTS , today's [ as of? ] usual RS-232 hardware flow control IEEE 802.11 RTS/CTS , wireless networking protocol flow control
Source: [1] Node D is unaware of the ongoing data transfer between node A and node B. Node D has data to send to node C, which is in the transmission range of node B. D initiates the process by sending an RTS frame to node C. Node C has already deferred its transmission until the completion of the current data transfer between node A and node B (to avoid co-channel interference at node B).
This UART introduces the Auto-RTS and Auto-CTS features in which the RTS# signal is controlled by the UART to signal the external device to stop transmitting when the UART's buffer is full to or beyond a user-set trigger point and to stop transmitting to the device when the device drives the CTS# signal high (logic 0). 16550A
If the channel is clear, the device can proceed with transmission. If the channel is busy, the device waits for a random amount of time before attempting to transmit. Additionally, devices may use Request to Send (RTS) and Clear to Send (CTS) messages to reserve the channel before transmitting data, further reducing the likelihood of collisions.
RTS/CTS is not a complete solution and may decrease throughput even further, but adaptive acknowledgements from the base station can help too. The comparison with hidden stations shows that RTS/CTS packages in each traffic class are profitable (even with short audio frames, which cause a high overhead on RTS/CTS frames).