Q classes
The ATM Forum and the ITU-T have classified the quality of service( QoS) and thus divided the services into specific QoS classes. The ATM Forum's classification distinguishes between four QoS classes, while the ITU-T has defined these in Recommendation Y.1541, Network Performance Objectives for IP-based Services, and distinguishes between eight QoS classes.
Theclassifications are about the performance requirements for IP-based applications. The eight QoS classes are numbered 0 to 7 and are for interactive data traffic, such as Internet telephony, Internet television or video conferencing, for runtime-sensitive applications, for multimedia data traffic and streaming and live streaming, and for sensitive interactive data traffic.
Therefore, applications are assigned to the individual QoS classes, as well as certain parameters that affect the traffic, such as the packet loss rate, the runtime and the jitter. As the QoS class increases, the packet loss rate decreases. The other two parameters are independent of the QoS class.