Integrated Services Digital Network (ISDN) - Call Forwarding Unconditional (CFU) supplementary service - Service description; English version ETS 300200:1994
Telecommunications Management Network (TMN) - Functional specification of Customer Administration (CA) on the Operations System/Network Element (OS/NE) interface - Part 1: Single line configurations
Integrated Services Digital Network (ISDN) - Selective Call Forwarding (SCF) supplementary services (unconditional, busy and no reply) - Service description