This Recommendation defines the stage 2 of the integrated services digital network (ISDN) as provided for the call waiting (CW) supplementary service.Stage 2 identifies the functional capabilities and the information flows needed to support the service description. The stage 2 description also identifies user operations not directly associated with a call (see Rec.1.130 [i]).This Recommendationis specified according to the methodology specified in Recommendation4.65 [2].This Recommendation does not formally describe the relationshipbetween this supplementary service and the basic call but,where possible,the information is included for guidance.In addition, this Recommendation does not speciQ the requirements where the service is provided to the user via a private ISDN. This Recommendation does not specify the requirements for the allocation of defined functional entities within a private ISDN;it does however define which functional entities may be allocated to a private ISDN.This Recommendation does not specify the additional requirements where the service is provided to the user via a telecommunications network that is not an ISDN.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 Recommendation is applicable to the stage 3 Recommendations for the ISDN CW supplementary service. The term "stage 3" is also defined in Recommendation I.130 [i]