Talk:Carrier-sense multiple access with collision avoidance: Difference between revisions
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shamefully deleted my own comment. I was wrong. --[[User:Alvestrand|Alvestrand]] 20:27, 18 January 2006 (UTC)
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*** '''802.3 Ethernet.''' A device (A) that is transmitting to another device (B) is able to listen to (sense) the cable while transmitting and thus detect a collision caused by an interfering device (C) on the local subnet directly. That is, Device A is able to receive the signal that it is putting onto the wire as well as the signal from device C. As does device B, but the superimposed signals are unintelligible and need to be re-transmitted which is why collisions are a source of data link inefficiency. At least both device A and C are aware that they need to re-transmit their respective frames.
*** '''802.11 RF.''' For the same situation above except that devices now have a radio frequency (RF) transceivers rather than cable. Because of the way that electromagnetic radiation propagates and the signal attenuates with distance. The radio signal that node A receives from interfering node C is many orders of magnitude (10's of dB's) less than the signal that itself (node A) is also transmitting. This means that node A is not able to discover that collision has occurred. This is why 802.11 employs acknowledgment fames (ACK) i.e. A node is thus able to detect a collision by the non-receipt of an ACK frame that would have been transmitted by node B if it had been able to make sense of the frame that node A had transmitted.
** The second is the ''collision avoidance - '''CA''' ''mechanism that Phil Karn gave us in [[MACA]]. Because of the nature of the wireless medium, there are situations in which better link performance results by nodes utilizing a short control frame (RTS/CTS) handshake to explicitly alert all nearby potentially interfering nodes of the impending DATA frame
*Therefore you are incorrect in stating that CSMA/CA does not use RTS/CTS, as this handshake is the CA part of CSMA/CA. [[User:DrBob127|DrBob127]] ([[User talk:DrBob127|talk]]) 03:09, 22 November 2008 (UTC)
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[[Special:Contributions/85.97.254.28|85.97.254.28]] ([[User talk:85.97.254.28|talk]]) 20:07, 11 May 2012 (UTC)
==Not only wireless==
It is important to concentrate on the protocol itself in the article. Yes, wireless is the most common current use, but that is by no means
==CS ''versus'' CA==
If [[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 transmission medium"'', then what does /CA add? This CSMA/CA article currently states that ''"...carrier sensing is used, but nodes attempt to avoid collisions by transmitting only when the channel is sensed to be "idle"..."'' - but surely this is true of CSMA/CD too? [[User:Snori|Snori]] ([[User talk:Snori|talk]]) 18:57, 26 June 2012 (UTC)
== Reason for using CSMA/CA over CSMA/CD ==
The article says that CSMA/CA is used in radio networks because CSMA/CD cannot solve the hidden terminal problem. While this is correct, the more important reason is imho that in radio networks, nodes are typically not able to transmit and receive at the same time (cf. also section "CSMA/CA does not use RTS/CTS"). Thus, it is typically not possible to implement CSMA/CD in a wireless network. This should imho be mentioned in the article.[[Special:Contributions/93.135.120.181|93.135.120.181]] ([[User talk:93.135.120.181|talk]]) 13:52, 6 October 2013 (UTC)
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