Difference between revisions of "Carrier-Sense Multiple Access with Collision Detection"
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'''Carrier-Sense Multiple Access with Collision Detection''' (often given as the acronym, '''CSMA-CD''') is a way of controlling access to a [[Local Area Network|LAN]] using a bus (i.e. a shared broadcast channel on which all stations can hear any station which is transmitting). | '''Carrier-Sense Multiple Access with Collision Detection''' (often given as the acronym, '''CSMA-CD''') is a way of controlling access to a [[Local Area Network|LAN]] using a bus (i.e. a shared broadcast channel on which all stations can hear any station which is transmitting). | ||
| − | What this means is that a station wanting to transmit waits until it hears silence ('carrier sense'), and then starts transmitting. If it 'hears' another station start to transmit while it is so doing (a 'collision' - hence 'collision detection'), it stops, 'backs off' a random delay, and re-tries. (This is essentially exactly identical to what a group of people chatting at a party will do.) | + | What this means is that a station wanting to transmit waits until it hears silence ('carrier sense'), and then starts transmitting. If it 'hears' another station start to transmit while it is so doing (a 'collision' - hence 'collision detection'), it stops, 'backs off' a random delay, and re-tries. (This is essentially exactly identical to what a group of people chatting at a party will do.) |
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| + | With both stations doing the 'random backoff after collision', the chances are that one will start before the other, and succeed in acquiring the channel: i.e. its new transmission will arrive at the other station, so it can suppress the other station from transmitting, before the second station's random time-out will have run out. | ||
A versions of CSMA-CA was first used on the [[ALOHA]] network, before being adopted for [[Ethernet|Experimental Ethernet]]. | A versions of CSMA-CA was first used on the [[ALOHA]] network, before being adopted for [[Ethernet|Experimental Ethernet]]. | ||
[[Category: Networking]] | [[Category: Networking]] | ||
Revision as of 00:54, 6 December 2018
Carrier-Sense Multiple Access with Collision Detection (often given as the acronym, CSMA-CD) is a way of controlling access to a LAN using a bus (i.e. a shared broadcast channel on which all stations can hear any station which is transmitting).
What this means is that a station wanting to transmit waits until it hears silence ('carrier sense'), and then starts transmitting. If it 'hears' another station start to transmit while it is so doing (a 'collision' - hence 'collision detection'), it stops, 'backs off' a random delay, and re-tries. (This is essentially exactly identical to what a group of people chatting at a party will do.)
With both stations doing the 'random backoff after collision', the chances are that one will start before the other, and succeed in acquiring the channel: i.e. its new transmission will arrive at the other station, so it can suppress the other station from transmitting, before the second station's random time-out will have run out.
A versions of CSMA-CA was first used on the ALOHA network, before being adopted for Experimental Ethernet.
