MC92501 Datasheet, PDF (6/52 Pages) Motorola, Inc – ATM Cell Processor

1.2. ATM Network Applications
The MC92501 performs the ATM layer functions in an ATM
switch such as cell processing and routing. Since the
MC92501 is an ATM layer device, it is PHY layer independent.
Figure 2 illustrates a typical ATM line card. The MC92501
uses an external memory for storing the cells that it
processes. In addition, the MC92501 offers an option to utilize
an external address compression device accessed via the
same external memory bus.
The microprocessor is used for conÞguration, control, and
status monitoring of the MC92501 and is responsible for
initializing and maintaining the external memory. The
MC92501 is the master of the external memory bus. At regular
intervals, the MC92501 allows the microprocessor to access
the external memory for updating and maintenance.
System RAM can also be located on the line card. The
MC92501 can support a DMA device to allow efÞcient data
transfer to this RAM without processor intervention.
The physical interface (PHY-IF) implements the physical
layer functions of the 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 (UNI) or between two ATM switches (NNI). The cells
are transferred between the physical interface and the
MC92501 using the UTOPIA Level 2 standard.
The MC92501 implements B-ISDN UNI/NNI ATM layer
functions required to transfer cells to and from the switch over
virtual connections. These functions include usage
enforcement, address translation, and Operation,
Administration, and Maintenance (OAM) processing. The
MC92501 provides context management for up to 65,536
(64K) Virtual Connections (VCs).The VCs can be either Virtual
Path Connections (VPCs) or Virtual Channel Connections
(VCCs). ATM cells belonging to a particular VCC on a logical
link have the same unique Virtual Path IdentiÞer/Virtual
Channel IdentiÞer (VPI/VCI) value in the cell header. Similarly,
cells belonging to a particular VPC on the same logical link
share a unique VPI.
RAM
MICRO-
PROCESSOR
D_DMM_AA
EXTERNAL
MEMORY
EXTERNAL
ADDRESS
COMPRESSION
MICROPROCESSOR BUS
CLOCK
RECOVERY
PPPHH^HYYI^YF-I-FIF
EXTERNAL
MEMORY
BUS
MC92501
TO SWITCH
FROM SWITCH
LINE CARD
Figure 2. Typical MC92501 Line Card Application
MC92501
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