CSMA CD (Carrier Sense Multiple Access Collision Detection)

The Collision Detection protocol, known as Carrier Sense Multiple Access/Collision Detection (CSMA/CD), is utilized to identify collisions within the media access control (MAC) layer. Upon detecting a collision, CSMA/CD promptly ceases transmission by transmitting a signal, thereby preventing the sender from wasting time on sending the data packet. If collisions occur from multiple stations while broadcasting packets, CSMA/CD rapidly transmits a jam signal to halt transmission and enters a random time delay before attempting to transmit another data packet. Once the channel is found to be free, it promptly sends the data and awaits a response.

Following are the process that CSMA/CD applies to avoid collision in a
shared channel

  1. Listen: Before transmitting, a station using CSMA/CD listens to the network to check if the channel is idle (no other station is transmitting).
  2. Carrier Sense: If the channel is sensed as idle, the station begins transmitting its data packet.
  3. Collision Detection: While transmitting, the station continues to monitor the channel for any collisions. If a collision is detected (i.e., another station is transmitting at the same time), it immediately stops transmitting and sends a jam signal.
  4. Backoff and Random Delay: After detecting a collision, the station enters a random backoff period. This helps to reduce the chances of collisions reoccurring. Each station generates a random delay before attempting to retransmit the data.
  5. Retry: After the backoff period, the station reattempts transmitting its data. It repeats the process from step 1 (listen), checking if the channel is idle. If the channel is still busy, the station extends the backoff period and retries again later.
  6. Successful Transmission: When the station successfully transmits the entire data packet without any collisions, it receives an acknowledgment (ACK) from the receiving station. This indicates that the transmission was successful.

Please note that CSMA/CD is primarily used in Ethernet networks, where it helps to manage multiple stations accessing the shared network medium and reduces the chances of collisions.

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