Electronic and Postal Communications (Quality of Service) G.N. No. 416 (contd) neither the call is answered nor the called party busy tone nor ringing tone is recognized at the access of the calling user within 40 seconds from the instant when the last digit of the destination subscriber number is received by the network. 5 R-Value Transmission Rating Factor R is the primary output of the E-model defined in ITU-T Rec. G.107/ G.108 For best quality: 90≤ R < 100 For high quality: 80 ≤ R < 90 For medium quality:70 ≤ R < 80 [ITU-T Rec. G.109] 6 Values on a predefined scale that subjects assign to their opinion of the performance of the telephone transmission system used either for conversation or for listening to spoken material. Apart from subjective opinion, the abbreviation "MOS" is also used for scores that originate from objective models or network planning models. Mean Opinion Score (MOS) Objective assessment based MOS should be greater than 4 on conversion of R-value. (ITU-T Rec. G.107) Subjective assessment based on use of telephone user surveys. (ITU-T Rec. P.82) 18