Overhearing

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Overhearing [ ˌoʊvəhiːɹɪŋ ] ( Engl. (To) overhear , "sth. Overhear accidentally") is called in computer networks the undesirable fact that a computer sound message exchange between two other computers on the network. This is undesirable in this case not for reasons of data protection or security - as the secondary meaning of "listening" to the term " overhear " might suggest - but from the purely technical point of view that the listener wastes time and energy because he does not information intended for him cannot do anything.

Overhearing occurs particularly when the computers in a network share a common transmission channel, for example a single radio frequency or a single data transmission cable. Constant listening to the transmission channel is a simple way of checking the carrier , i.e. to find out whether the medium is free and therefore available for your own data exchange. However , overhearing should be avoided, especially in resource - critical networks such as ad hoc networks , because constant listening in puts too much strain on the limited capacities of the end devices involved (energy reserve for battery-operated devices, computing time for fieldbus systems , ...).

remedy

There are different approaches to minimize overhearing. One is sending additional information about how long a data exchange is likely to take. The eavesdropper can deduce from this that the transmission channel will only become free again after this period of time has elapsed and during this time he will refrain from listening to the medium (virtual carrier test) . Another approach is the use of time windows in the context of time division multiple access , which means that communications are only allowed to begin at regular time intervals. Instead of constantly listening to the medium, the listener can limit himself to performing the carrier test only at these fixed times.

literature

  • Mihaela Cardei: Resource management in wireless networking . In: Network Theory and Applications . tape 16 . Springer, 2005, ISBN 0-387-23807-7 , pp. 306 ( limited preview in Google Book search).
  • Jun Zheng, Abbas Jamalipour: Wireless Sensor Networks: A Networking Perspective . John Wiley & Sons, 2009, ISBN 978-0-470-16763-2 .