Qos - Quality Of Service

In computer networking, QoS (Quality of Service) refers to bandwidth control mechanisms. Quality of service is the capability to provide different priority to different applications, users, or data flows, or to assure a certain level of bandwidth to a data flow. For example, an essential bit rate, packet delay, packet dropping probability and/or packet corruption rate may be guaranteed. Quality of service control mechanisms are important if the network capacity is inadequate, especially for streaming multimedia programs such as VOIP and IPTV, as these usually require fast bit rate and are delay sensitive. In the absence of traffic congestion in the network, QoS mechanisms are not required.

Qos mechanisms are intended to handle problems what bandwidth or data compression techniques alone cannot i.e., guaranteed timely delivery of application data or resources to a particular target. A network or protocol that supports QoS may have a traffic agreement with the application and reserve the required capacity in the network nodes, for example during establishing a session. During the session it would study the level of performance, i.e. the data rate and delay, and dynamically control and schedule priorities in the network. It may release the reserved capacity when the application is no longer being used.


An alternative to the complex QoS mechanisms is to provide high bandwidth communication line over a network by increasing the capacity such that it is adequate for the expected peak traffic load.

By: Roberto Bell

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John Cicero writes on topics such as QoS, 802.1p, and VoIP for The Tech FAQ.

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