In a typical line card, the MC92520 serves as an interface between a physical layer device and an ATM switch matrix. The MC92520 uses a fast external memory for storing the ATM virtual connection information for the cells it processes. The microprocessor is used for configuration, control, and status monitoring of the MC92520 and is responsible for initializing and maintaining the external memory. The MC92520 is the leader of the external memory bus. At regular intervals the MC92520 allows the microprocessor to access the external memory for updating and maintenance.
The physical interface (PHY-IF) implements the physical layer functions of the broadband ISDN (B-ISDN) protocol reference model. This includes the physical medium dependent functions required to transport ATM cells between the ATM user and the ATM switch (i.e., a user-network interface or UNI) or between two ATM switches (i.e., a network-node interface or NNI). The cells are transferred between the physical interface and the MC92520 using the UTOPIA standard. The MC92520 implements ATM layer functions required to transfer cells to and from the switch over virtual connections. These functions include usage enforcement, address translation, and operation and maintenance (OAM) processing.