CSMA/CARP

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In computer networking, Carrier Sense Multiple Access with Collision Avoidance and Resolution using Priorities (CSMA/CARP) is a channel access method. CSMA/CARP is similar in nature to the CSMA/CD Channel access method used in Ethernet networks, but CSMA/CARP provides no detection of network collisions. Instead of detecting network collisions, CSMA/CARP attempts to avoid collisions by using a system of transmission priorities. Again, CSMA/CARP is similar to the functions of the CSMA/CA. However, the /CA (Collision Avoidance) employs a different approach of how to make packets get transmitted over the wire or medium without any difficulties.

When a station wants to transmit on a CSMA/CARP network it first listens for network traffic and if the medium is clear instead of immediately transmitting as a station would in CSMA/CD it waits a predefined amount of time. This waiting period is called the interframe spacing (IFS) and it varies by the type of data being transmitted. High priority data will transmit almost immediately whereas lower priority data such as polling will have a longer IFS. This system allows CSMA/CARP to avoid many collisions that would occur if it was not used. In addition to having a different IFS per priority, a station in a CSMA/CARP network will add a "random backoff" to its waiting period, to reduce the collision probability between stations that have to transmit packets in the same priority.

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