Given the number of calls that need to be carried, the peak cell rate for structured N???64 basic service for VTOA networks can be computed as: PCR = ( 8000 ??? N ) 46.875 ??? ??? cells ??? ??? per ??? ??? second Eq . ??? ( 4 ) ??? However, peak cell rate formulation for other types of services such as unstructured BS1/E1/DS3/E3, DS1/E1 with CAS can be found in ATM forms CES Interoperability Speci