ETSI Technical Report ETR 250, Transmission and Multiplexing (TM); Speech communication quality from mouth to ear for 3,1 kHz handset telephony across networks, ETSI 1996

This ETR applies to mouth to ear narrowband (nominally 3,1 kHz) telephony connections via handsets across one or more telecommunications networks of any type, public or private, fixed or mobile.
The objective is to assist network operators in ensuring that users will be satisfied with the transmission performance whilst avoiding over-engineering of the networks. The aim is to give realistic, practical guidance rather than a scientifically exact treatment of quality factors. It should be noted that the computational planning method, which is described in clause 9, has not yet been fully verified and may give incorrect results. Until this verification has been completed, predictions resulting from the use of this planning method should therefore be treated with caution. [see also ITU-T Recommendation G.107]