Network Service Access Point (NSAP) is a term from the OSI terminology. Network Service Access Point defines the point at which network services are made available to the transport layer.
This service access point is uniquely defined by a network address. One such address consists of 20 octets.
ATM uses the NSAP address structure for private network addresses. For public ATM addresses, ATM uses the E.164 standard of the International Telecommunication Union( ITU).