This ITU-T Recommendation deals with the digital interconnection of public ISDN/PSTN and private networks. The primary application is to the overall quality of speech transmission for 3.1 kHz voiceband telephony using handsets, independent of all other types of services (e. g. facsimile and voiceband data) provided by those networks. The intention is to give guidance for transmission planning purposes, not only for a given network operator, but also for negotiations between the involved network operators.