This standard provides the signaling and data transmission requirements associated with Call Waiting (CW), Distinctive Call Waiting (DCW), and Calling Identity Delivery on Call Waiting (CIDCW) features on analog voicegrade switched access lines. When the network provides the CW or DCW feature, a customer installation (CI), while off-hook on an existing call, receives a CW alerting tone or a DCW alerting tone pattern when an incoming call is waiting to be answered. When the network provides the CIDCW feature, a CI, while off-hook on an existing call, receives a CW alerting tone and an analog frequency-shift-keying (FSK) data message or a DCW alerting tone pattern and an analog FSK data message when an incoming call is waiting to be answered. This standard is intended to be used in conjunction with American National Standard for Telecommunications - Interface Between Carriers and Customer Installation - Analog Voicegrade Switched Access Lines Using Loop-Start and Ground-Start Signaling, ATIS-0600401.2000(R2005), and American National Standard for Telecommunications - Network to Customer Installation Interfaces - Analog Voicegrade Switched Access Lines with the Calling Number Delivery, Calling Name Delivery, or Visual Message Waiting Indicator Feature, T1.401.03-1998. Formerly known as T1.401.04-2000(R2005).