CSMA or CD

CSMA or CD

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is a media access control method used in Ethernet networks to prevent data collisions between multiple devices that are attempting to transmit data simultaneously on the same network segment.

In a CSMA/CD network, devices listen to the network to see if the medium is available (i.e., not currently in use by another device) before attempting to transmit data. If the medium is busy, the device waits until it becomes idle before transmitting. However, if two or more devices transmit data at the same time, a collision occurs, and both devices stop transmitting and wait for a random amount of time before attempting to transmit again. This random delay helps to prevent another collision from occurring immediately after the first one.

CSMA/CD was used in earlier Ethernet technologies, such as 10BASE-T and 100BASE-TX, but is not used in modern Ethernet networks that use full-duplex communication. Full-duplex communication allows devices to simultaneously send and receive data on separate channels, eliminating the need for collision detection.

It prevents collisions and procedure to follow when a collision occur. Steps are as

• Source listens until the Ethernet is not busy for sending a frame.
• If Ethernet is not busy, the sender sends the frame and then listens for no collision occurrence.
• If collision occurs, the devices that had been sending a frame each send a jamming signal to ensure that all nodes on network recognize the collision.
• After completing jamming, every sender waits a random time before resending collided frame.
• After each random time expiry, the process starts over with first step.

CSMA/CD are methods for collision detection are media dependent, but on an electrical bus. CSMA/CD determines how network devices respond when two devices attempt to use a data channel simultaneously. The CSMA/CD method is internationally standardized in IEEE 802.3 and ISO 8802.3.

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