In computer networking, CSMA/CA belongs to a class of protocols called multiple access methods. CSMA/CA stands for: Carrier Sense Multiple Access With Collision Avoidance. In CSMA, a station wishing to transmit has to first listen to the channel for a predetermined amount of time so as to check for any activity on the channel. If the channel is sensed "idle" then the station is permitted to transmit. If the channel is sensed as "busy" the station has to defer its transmission. This is the essence of both CSMA/CA and CSMA/CD. In CSMA/CA (LocalTalk), once the channel is clear, a station sends a signal telling all other stations not to transmit, and then sends its packet. In Ethernet 802.11, the station continues to wait for a time, and checks to see if the channel is still free. If it is free, the station transmits, and waits for an acknowledgment signal that the packet was received. This article or section is in need of attention from an expert on the subject. ...

Details

CSMA/CA is a modification of pure Carrier Sense Multiple Access (CSMA). Collision avoidance is used to improve the performance of CSMA by attempting to be less "greedy" on the channel. If the channel is sensed busy before transmission then the transmission is deferred for a "random" interval. This reduces the probability of collisions on the channel. Carrier Sense Multiple Access (CSMA) is a probabilistic Media Access Control (MAC) protocol in which a node verifies the absence of other traffic before transmitting on a shared physical medium, such as an electrical bus, or a band of electromagnetic spectrum. ...

CSMA/CA is used where CSMA/CD cannot be implemented due to the nature of the channel. CSMA/CA is used in 802.11 based wireless LANs. One of the problems of wireless LANs is that it is not possible to listen while sending, therefore collision detection is not possible. Another reason is the hidden terminal problem, whereby a node A, in range of the receiver R, is not in range of the sender S, and therefore cannot know that S is transmitting to R. In computer networking, Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a network control protocol in which (a) a carrier sensing scheme is used and (b) a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam signal, and then... IEEE 802. ... The notebook is connected to the wireless access point using a PC card wireless card. ... The notebook is connected to the wireless access point using a PC card wireless card. ... In computer networking, the hidden node problem occurs when a node is visible from a wireless hub, but not from other nodes communicating with said hub. ...

CSMA/CA can optionally be supplemented by the exchange of a Request to Send (RTS) packet sent by the sender S, and a Clear to Send (CTS) packet sent by the intended receiver R, alerting all nodes within range of the sender, the receiver, or both, to keep quiet for the duration of the main packet. This is known as the IEEE 802.11 RTS/CTS exchange. RTS/CTS (Request to Send / Clear To Send) is the mechanism used by the 802. ...

Usage

• GNET - an early proprietary LAN protocol
• 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 (Wireless PAN) uses CSMA/CA
• NCR WaveLAN - an early proprietary wireless network protocol

OKAN LOVES BIG MEN Lan can stand for several things: A local area network Lan (airline) formerly LanChile Lan Peru Län, a kind of administrative division used in Sweden Lan Mandragoran, a fictional character in the Wheel of Time fantasy series by Robert Jordan. ... Apple Inc. ... LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. ... RTS/CTS = Request to Send / Clear To Send A sending node wishing to send data sends a Request to Send frame. ... Wikipedia does not yet have an article with this exact name. ... IEEE 802. ... IEEE 802. ... WaveLAN is a trade name that describes two completely different families of wireless network solutions: Pre-IEEE 802. ...

See also

• Carrier sense multiple access with collision detection (CSMA/CD)

- a different approach to the same problem; used for Ethernet

In computer networking, Carrier Sense Multiple Access With Collision Detection (CSMA/CD) is a network control protocol in which a carrier sensing scheme is used and a transmitting data station that detects another signal while transmitting a frame, stops transmitting that frame, transmits a jam signal, and then waits for... Ethernet is a large, diverse family of frame-based computer networking technologies that operate at many speeds for local area networks (LANs). ...

References

• American National Standard T1.523-2001, Telecom Glossary 2000