"This standard defines the stage one of the pan-European Integrated Services Digital Network (ISDN) as provided by European public telecommunications operators. Stage one is an overall service description from the user's point of view@ but does not deal with the details of the human interface itself (see CCITT Recommendation I.130 [1]. This standard defines the interworking requirements of private ISDNs with the public ISDN. In addition this standard specifies the base functionality where the service is provided to the user via a private ISDN. This standard does not specify the additional requirements where the service is provided to the user via a telecommunications network that is not an ISDN but does include interworking requirements of other networks with the public ISDN. Charging principles are outside the scope of this standard. Interactions with supplementary services not listed in Clause 8 are outside the scope of this standard. The CW supplementary service permits a subscriber to be notified of an incoming call (as per basic call procedures) with an indication that no interface information channel is available. The user then has the choice of accepting@ rejecting or ignoring the waiting call (as per basic call procedures). The CW supplementary service is considered meaningful when applied to the telephony teleservice and the speech and 3@1 kHz audio bearer services. Furthermore@ it may also be meaningful when applied to other services. This standard is applicable to the stage two and stage three standards for the ISDN CW supplementary service. The terms ""stage two"" and ""stage three"" are also defined in CCITT Recommendation I.130 [1]. Where the text indicates the status of a requirement@ (i.e. as strict command or prohibition@ as authorisation leaving freedom@ as a capability or possibility@ this shall be reflected in the text of the relevant stage two and stage three standards. Furthermore@ conformance to this standard is met by conforming to the stage three standards with the field of application appropriate to the equipment being implemented. Therefore no method of testing is provided for this standard."