The present document defines protocols for the synchronization and aggregation of multiple Integrated Services Digital Network (ISDN) channels at 64 kbit/s, these channels having 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