Class of service

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In networks, class of service (CoS) refers to the segmentation of transit items into distinct groups, each of which requires (or is promised) different treatment in and by the network, or by the end applications, users, or devices.

The U.S. postal service implements a class of service capability; you can purchase priority overnight, 2nd day, first class, or bulk rate delivery. The airline industry also provides classes of service in the form of first class, business class, economy class, and (on some airlines) steerage.

In a communications network, a network administrator might place email and file transfer in one class of service and video in another. Each CoS is assigned its own service characteristics. In this example, the video traffic might be placed in a queue that receives priority treatment compared with the queue for email traffic.

In communications networks, there are many mechanisms by which a given packet or frame can be marked with its CoS membership. Some of them include Diffserv, 802.1p, and the ATM VPI/VCI (because each ATM virtual circuit. In frame relay the Discard Eligible (DE) bit can be thought of as providing a CoS capability.

See Also

PodSnacks

<mp3>http://podcast.hill-vt.com/podsnacks/2007q1/cos-qos.mp3%7Cdownload</mp3> | CoS vs. QoS