This ETS provides for synchronisation and aggregation of multiple ISDN channels at 64 kbit/s@ these channels being with a differential delay in the range of ?? one second and with or without octet integrity structure. It also addresses the case of interworking with a digital network restricted to a rate of 56 kbit/s. It is applicable to a wide range of user data transport up to 63 channels using ISO/IEC 13871 [1]@ but special provision is made for audiovisual systems according to ETS 300 144 [2]@ up to 24 channels; the aggregation may be network-based or associated with Customer-Premises Equipment. The available operating modes (B1@ B2@ B3@ H2) provide options with/without transmission-management overhead and user-data rates at or less than the exact multiples of 64 kbit/s or 56 kbit/s. The number of aggregated channels may be varied dynamically during a session. Procedures are given for dealing with faults@ including loss of channels and slip. Call control is outside the scope of this ETS.