MC92501 Datasheet, PDF (5/52 Pages) Motorola, Inc – ATM Cell Processor

SECTION 1. ATM NETWORK
1.1. ATM Network Description
A typical ATM network consists of user end stations that
transmit and receive 53-byte data cells on virtual connections
(see Figure 1). Physical links and switching systems
interconnect the virtual connections. A virtual connectionÕs
path is established at the beginning of the data transfer,
maintained while the end-stations are communicating, and
torn down after the transfer is complete. This transmission
method increases the transfer speed because the
determination of the path the data will take is done only at the
beginning of the data transfer instead of when each data sub-
block or packet is transferred.
On a given physical link, each connection is assigned a
unique connection identiÞer. The connection identiÞer is
placed in the header of each cell by the transmitting equipment
and is used by the receiving equipment to route the cell to the
next physical link on the connection path. All cells belonging
to a speciÞc virtual connection follow the identical path from
the transmitting end station through the switching systems to
the receiving end station.
An ATM switch contains a high-speed switching fabric that
connects multiple line cards.The switching fabric connects the
input port to the output port based on the switchÕs routing table.
The line card interfaces between the physical medium and the
switching fabric by recovering incoming cells from the arriving
bit stream or converting outgoing cells into a bit stream for
transmission. An ATM swtich partitioned in this fashion can
efÞciently handle multiple physical links by independently
transferring each incoming ATM cell from its source port to its
destination port, based on the switchÕs routing table.
ATM standards divide the tasks to be performed on each
side of the switch fabric into PHY layer and ATM layer tasks.
The PHY layer tasks are dependent on the physical medium
that connects ATM switches. The ATM layer tasks operate at
the cell level and are independent of the physical medium.
VCs
END STATIONS
Switch
Switch
Switch
Switch
Switch
VCs
Switch
END STATIONS
SWITCH
LINE
CARD
SWITCHING FABRIC
LINE
CARD
CLK REC
PHY
MC92501
ATM LAYER FUNCTIONS
LINE CARD
Figure 1. MC92501 in an ATM Network Application
MOTOROLA
MC92501
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