H.323 Endpoints

Because there are different H.323 endpoints based on different versions of H.323, the DTMF can be either be transferred out-of-band as UII or in-band using RFC 2833. Most H.323 endpoints:

version 4 and above support RFC 2833
version 2 and pre-version 4 support UII-Signal
version 1 and pre-version 2 support UII-Alphanumeric