This Recommendation specifies an approach for the performance description of AAL processes [1]. It is motivated by the need@ based on field experiences@ to examine more carefully the performance aspects of some specific applications of ATM network technology. The approach provides a unified framework for describing the performance of a process that depends upon AAL Type 1 (AAL-1) [2]@ AAL Type 2 (AAL-2) [3]@ AAL Type 3/4 (AAL-3/4) [4]@ AAL Type 5 (AAL-5) [5]@ or potentially other types of AAL. The Recommendation defines measurement points and reference events for all AAL types@ and uses these to define PDU transfer outcomes and AAL performance parameters for AAL Type 5 (PDU transfer outcomes and AAL performance parameters for other AAL Types are FFS).