CoS (class of service) enables more predictable traffic delivery of priority data across IP-enabled ATM or frame relay networks by assigning different delivery status for each application.
A "first class" priority label is assigned to data applications - such as mission-critical data transactions, or video or voice transmissions - which require faster turnaround, while a lower-priority label is assigned to less time-sensitive traffic, such as e-mail and Web surfing.
Traffic is delivered around the world based on a company's designated priority, and is usually backed by stringent service-level guarantees from the service provider.
CoS differs from QoS in that QoS refers to a level of service in terms of bandwidth or delivery time, such as bandwidth prioritization or traffic shaping, while CoS refers to traffic delivery priorities. IP-enabled frame relay and ATM let users take advantage of the benefits of QoS and CoS technologies.
Here's how CoS works: Based on application requirements, traffic is prioritized at the connection endpoint by setting the Differentiated Services (Diff-Serv) code in the header of an IP data packet. Letting users manage network traffic, Diff-Serv is the protocol used to prioritize data traffic.
From CoS offers prioritization on private nets, Network World, 05/13/02.
