Abstract: The present invention uses the SAR and CPCS functions of the AAL-5 to define an AAL-5 SSCS for performing the AAL-1 and AAL2 functions. The defined AAL-5 format comprises a SSCS trailer of N (preferred value is 8) bytes an CPCS-PDU of N+8 (preferred value is 16) cells (16.times.48 bytes=768 bytes). In the preferred embodiment, the AAL-5 CPCS-PDU is transported inside 16 ATM cells. The CPCS and SSCS trailers provide the the same efficiency as AAL-1 and the global structure based on 16 cells is completely similar and transparent in term of delay and overhead. The payload size is 48 bytes for the 15 first cells, and 32 bytes for the last cell. The CPCS-PDU payload size is always a multiple of 8 bytes.