Which standard will support call forwarding?

H.450.3 is an ITU-T supplementary services standard that defines call forwarding (including forward unconditional, forward on busy, and forward on no reply) for H.323 endpoints and gatekeepers. It extends the base H.323 protocol with the specific signaling messages and procedures needed to redirect calls. Without H.450.3, H.323 systems have no standardized mechanism for call forwarding.

H.323 is the overarching umbrella standard for multimedia communications over packet networks; it defines the framework but does not itself specify call forwarding - that is delegated to the H.450.x supplementary service series.

RFC 2833 defines the transport of DTMF and other telephony tones as named telephony events over RTP, which has no relation to call forwarding signaling.

H.450.2 defines call transfer supplementary services (moving an established call to a third party), not call forwarding - the two are distinct operations with different H.450.x designations.