ITU-T Recommendations

This Recommendation gives a framework and definitions for communications quality of service so as to establish a uniform approach to quality of service across the ITU-T and eliminate the confusion resulting from different frameworks and inconsistent definitions. Improved consistency regarding quality of service is needed throughout the communications industry, especially in IP-related areas within and outside the ITU.This Recommendation provides a practical "top-down" path from a general quality definition (ISO 8402) to a QoS definition (ITU-T Rec. E.800) to network performance (ITU-T Rec. I.350, and Y.1540) to a functional breakdown of all components of service quality (the QoS definition matrix of ETSI ETR 003). Additionally presented are four viewpoints of QoS that make the definitions and framework meaningful for everyone: users, vendors, network operators, service providers, etc. This overall approach is believed to be highly useful because it encourages a consistent and uniform mapping between the top-down, framework definitions of QoS and the bottom-up, operational measures on network elements. Advantages of using this approach is that it not only helps identify QoS-related problems, but it also facilitates quantifying the problem from multiple views; the customer's (e.g. surveys and subjective tests) and the service provider's (network measurements). This helps assure that resolving the problem in one domain (e.g. the provider) also resolves it in the other (e.g. the customer).