CSMA/CD and CSMA/CA Clarified

CSMA/CD (Carrier Sense Multiple access/Collision Detection) and CSMA/CA (carrier Sense Multiple Access/Collision Avoidance) are algorithms used for multiple access channel allocation in telecommunication.

CSMA/CD is collision contention protocol;

Before a device send a data,It senses the channel and will transmit only if the channel is available.When two devices send data simultaneously collision occur because the protocol didn’t set any rule on the time at which a transmission can occur and for that matter it is possible that two devices may sense the medium at the same time and therefore can transmit simultaneously when the channel is sensed free by both; When this happens,all other devices on the network are aware of the collision because the channel will be busy when it is sensed. Therefore they wait for a random time period and sense the channel again before transmission.

CSMA/CD is standardized for transmission in Ethernet 802.3 network channel. CSMA/CD has no mechanism to avoid the collision rather react to it as it occurs. As a result when collision is persistent due to network congestion, its performance drop and more capacity is not utilized when long frames are transmitted in the channel.

CSMA/CD used in Ethernet, cannot be used for the radio frequency transmissions of IEEE 802.11.The reason is that when a node is transmitting it cannot hear any other node in the system which may be transmitting, since its own signal will drown out any others arriving at the node.

CSMA/CA is derived from CSMA/CD and has a mechanism to avoid collision by defining a time when a device can sense and when it can transmit a data through the channel.

CSMA/CA is used in wireless transmission. CSMA/CA has better performance than CSMA/CD because it keeps transmitting even when there is collision in the channel

“An ad hoc network is a collection of communicating nodes that do not have established infrastructure or centralized administration. CSMA/CA protocol is useful in ad hoc networks where access to the network is decentralized since each station coordinates its own decisions for accessing the medium. There is no central 346 10 Modeling Medium Access Control Protocols access point to coordinate activities of all station. Thus ad hoc networks are simpler to implement and to modify. The price for this simplicity is that ad hoc networks are prone to collisions” Fayez Gebali — Analysis of computer and communication network.

My small tip to remember is that Collision Detection is Red =Bad and Collision Avoidance is Green=Good.(In terms of efficiency)[In Wireless Communication ]

CSMA/CA is generally used in wireless networks

CSMA/CD is generally used in wired networks