call forwarding unconditional (ISDN) (CFU)

Call Forwarding Unconditional (CFU) is a feature of call forwarding where call forwarding is permanently activated. With this feature of ISDN and mobile networks, all incoming calls are forwarded to another phone number. Unconditional refers to the fact that call forwarding is not linked to any condition.

However, there are also selective criteria for activating unconditional call forwarding, as Selective Call Forwarding Unconditional (SCFU), Selective Call Forwarding on No Reply (SCFN), and Selective Call Forwarding on Busy (SCFB). These are the immediate call forwarding and the delayed by several seconds. This CFU call forwarding is described in ITU-T Recommendation ITU-T I.252.