This Recommendation applies to digital local, combined, msit and intemational exchanges for telephony in Integrated Digital Networks (IDN) and mixed (analoguddigital) networks, and also to local, combined, transit and international exchanges in an Integrated Services Digital Network (ISDN). The field of application of this Recommendation is more fully defined in Recommendation QS??. Some objectives only apply to a ceriain type (or types) of exchange. Where this occurs, the application is defined in the text. Where no such qualification is made, the objective applies to all exchange applications.