Introduction Videoconferencing and visual telephony are new services which require greater bit rates than telephony. In the studies in CCITT on the ISDN and on international interworking@ 384 kbit/s is emerging as an important channel capacity for wideband services. On this basis it is recommended that the videoconferencing and visual telephone services should be based on multiples of 384 kbit/s. It is noted that both the 2048 kbit/s and 1544 kbit/s primary digital levels can be expressed by the formula y + (n x 384) kbit/s@ where n = 5 or 4 and y = 128 or 8 kbit/s@ respectively. While this Recommendation covers only frame structures for transmission at the primary digital rates@ it is not intended to suggest that transmissions using other frame structures or formats at primary rates or lower are precluded. In the future@ frame structure based on other multiples and/or sub-multiples of 384 kbit/s may also be considered.