Data collision

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In computer networks, data collision is the undesirable circumstance that data is lost because two computers are transmitting simultaneously over the same communication medium. The signals sent are superimposed in the medium, so that both messages can no longer be deciphered. Since the data in computer networks are usually divided into data packets , one also speaks of packet collision .

Collision avoidance

Avoiding data collisions is one of the central concerns in computer networks with a common communication medium. The main approach to avoid is the carrier sense (carrier sense) , that is the review before sending, whether the medium is truly free. A significant process that implements carrier testing is Carrier Sense Multiple Access .

Carrier Sense Multiple Access / Collision Detection (CSMA / CD) is a special form of carrier testing , which is used in Ethernet , among other things . The test takes place here not only before, but during the transmission. All networked computers constantly monitor the medium. If two computers randomly send at the same time, so that a data collision occurs, the computer that notices the collision first sends a jamming signal . The other computers recognize this as an error message and only start sending again after a random period of time.

In some combinations of network topology and network protocol , collisions are systematically excluded. For example, a token ("voucher") is passed on in a token ring , which is the only one that allows its owner to send; the computer is spoken "given the floor".

Collision probability

The higher the network load, i.e. the more computers are involved in the network and the more often and longer they want to send, the higher the probability of a data collision without precautionary measures. This can be determined mathematically using a probability calculation.

See also

Individual evidence

  1. Packet collision. Retrieved October 12, 2018 .
  2. The foundation: CSMA / CD. Retrieved October 12, 2018 .
  3. CSMA / CD - Carrier Sense Multiple Access with Collision Detection. Retrieved October 12, 2018 .
  4. Comparison between CSMA / CD and Token Ring Mac Algorithms AND Bridges LANs. (PDF) Accessed October 12, 2018 (English).