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CoS (Class of Service)

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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

CoS-not to be confused with QoS (Quality of Service)-is a form of priority queuing that has been used in a number of communication and networking protocols. It is a way of classifying and prioritizing packets based on application type (voice, video, file transfers, transaction processing), the type of user (CEO, secretary), or other settings.

CoS is a queuing discipline while QoS covers a wider range of techniques to manage bandwidth and network resources. CoS classifies packets by examining packet parameters or CoS markings and places packets in queues of different priorities based on predefined criteria. QoS has to do with guaranteeing certain levels of network performance to meet service contracts or to support real-time traffic. With QoS, some method is used to reserve bandwidth across a network in advance of sending packets.

As an analogy, CoS is like classifying packages for delivery via regular mail, second-day delivery, or next-day delivery. QoS is what the delivery company does to ensure your packages are delivered on time (such as package tracking, air transport, door-to-door pickup and drop-off).

This topic continues in "The Encyclopedia of Networking and Telecommunications."

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