Telecommunications and Internet Protocol Harmonization over Networks (TIPHON); End to End Quality of Service in TIPHON Systems; Part 2: Definition of Quality of Service (QoS) Classes (V1.1.1)
"The present document defines four classes of Quality of Service for characterizing the performance of TIPHON compliant IP voice telephony networks. The classes of service apply to all the defined TIPHON Scenarios. The classes are specified in terms of ""Overall Transmission Quality Rating""@ ""Listener Speech Quality"" (one-way noninteractive speech quality) and ""End-to-end Delay""."