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Collision Avoidance

Definition - What does Collision Avoidance mean?

Collision avoidance techniques are used in telecommunications and computer networks to avoid resource contention. These techniques attempt to eliminate situations in which multiple nodes access the same resource. This ensures that any node in a network can transmit a signal without colliding with other traffic on the network.

Techopedia explains Collision Avoidance

A few of the most commonly used collision avoidance methods include:

  • Carrier detection schemes
  • Prior scheduling of time slots
  • Randomized access times
  • Exponential back off after collision detection

Collision avoidance in networking mainly appears in networks with carrier sense multiple access (CSMA). This is based on the principle that nodes that are willing to transmit data have to listen to the channel for some time to determine whether other nodes are also transmitting on the wireless channel. A node can start transmission only if a channel appears to be idle, otherwise, transmissions are deferred. Collision avoidance improves CSMA performance by stopping multiple nodes from transmitting at the same time. The likelihood of collision is reduced by using random truncated binary exponential back-off time.

Collision avoidance divides the wireless channels equally among transmitting nodes within the collision domain. It’s supplemented by exchanging requests to send a packet. Nodes within senders and receivers are alerted not to transmit for the duration of main transmissions.

One popular avoidance scheme has a sender-initiated four-way handshake, where transmission of a data packet and acknowledgment of its receipt are preceded by a request to send and a clearance to send. The nodes that overhear these packets defer their channel access to avoid collisions.

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