H.321 is the ITU standard for video conferencing over B-ISDN and ATM. This ITU standard is from 1995 and deals with the adaptation ofH.320videophones
to the ATM network. The standard defines video compression (H.262, H.263), audio compression according to G.711 and G.722, multiplexing according to H. 221 and multipoint connections (H.231, H.243). Data transmission is carried out according to the T.120 standard and for transport H.321 specifies the ATM Adaption Layer (AAL).