What is a CD (Communication deflection)?

Call deflection is an attribute of voice-over IP (VoIP) that diverts a call from the called endpoint to another endpoint when the called endpoint is occupied. Call deflection is one of few types of call forwarding characterized under the H.450.3 specification.
There are three communications points in call deflection, alluded to as the beginning gateway, the deflecting gateway, and the deflected-to gateway.