Call if Forwarding Busy (CFB) is a feature ofdigitalcommunication networks that activates call forwarding (CF) in the event of a busy call. In the busy case, the local exchange transfers the incoming call to a specified call number
. TheCFB function can be related to specific calls and services
. Since call forwarding is performed in the exchanges, it also takes place when the call number is suppressed, Calling Line Identification Restriction (CLIR). Call forwarding on busy is described in ITU-T Recommendation I.252, Call termination supplementary services.