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PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
3
FUNCTIONAL DESCRIPTION
The XRT7245 UNI can functionally be subdivided in-
to 6 different sections, as shown in Figure 1.
Receive Section
Transmit Section
Microprocessor Interface Section
Performance Monitor Section
Test and Diagnostic Section
Line Interface Unit Scan Drive Section
The features of each of these functional sections are
briefly outlined below.
THE RECEIVE SECTION
The purpose of the Receiver Section of the XRT7245
DS3 ATM UNI device is to allow a local ATM Layer (or
ATM Adaptation Layer) processor to receive ATM cell
data from a remote piece of equipment via a public or
leased DS3 transport medium.
The Receive Section of the XRT7245 DS3 UNI con-
sists of the following functional blocks.
Receive DS3 Framer Block
Receive PLCP (Physical Layer Convergence Proto-
col) Processor Block
Receive Cell Processor Block
Receive UTOPIA Interface Block
The Receive Section of the UNI device will:
The Receive DS3 Framer will synchronize to the
incoming DS3 data stream and remove or process
the DS3 Framing/Overhead Bits. This procedure
will result in either extracting PLCP frame data or
“Direct-Mapped” ATM Cell data, from the payload
portion of the incoming DS3 data stream. The
Receive DS3 Framer can used to receive FEAC
(Far End Alarm & Control) messages via an on-
chip FEAC Transceiver.
Additionally, the Receive DS3 Framer includes an on-
chip LAPD Receiver that can receive incoming path
maintenance data link messages from the far-end
Transmit DS3 Framer of the “Far End” Terminal.
Note:
The Receive DS3 Framer supports both M13 and C-
bit Parity Frame Formats.
The Receive PLCP Processor will identify the
frame boundary of each incoming PLCP frame,
extract and process the overhead bytes of these
PLCP frames (applies only if the UNI is operating in
the PLCP Mode). The Receive PLCP Processor
will also perform some error checking on the
incoming PLCP frames. The Receive PLCP Pro-
cessor will inform the Far-End (Transmitting UNI) of
the results of this error-checking by internally rout-
ing these results to the “Near-End” Transmit PLCP
Processor, for transmission back out to the Far-End
Terminal.
The Receive Cell Processor will perform the follow-
ing functions:
– Cell Delineation
– HEC Byte Verification of incoming cells
(optional)
– Cell-payload de-scrambling (optional)
– Idle cell detection and removal (optional)
– User and OAM Cell Filtering (optional)
– OAM Cell Processing (optional)
The UNI provides 54 bytes of on-chip RAM that
allows for the reception and processing of selected
OAM cells.
The RxFIFO, within the Receive UTOPIA Interface
block will temporarily hold any ATM cells that pass
through the Receive Cell Processor, where they can
be read out by the ATM Layer processor, over the
Receive UTOPIA Data Bus.
THE TRANSMIT SECTION
The purpose of the Transmit section of the XRT7245
DS3 ATM UNI device is to allow a local ATM Layer (or
ATM Adaptation Layer) processor to transmit ATM
Cell data to a remote piece of equipment via a public
or leased DS3 transport medium.
The Transmit Section of the XRT7245 DS3 UNI con-
sists of the following functional blocks.
Transmit UTOPIA Interface Block
Transmit Cell Processor Block
Transmit PLCP Processor Block
Transmit DS3 Framer Block
The Transmit Section of the UNI device will:
Allow the ATM Layer processor to write ATM cells
into the Transmit FIFO (within the Transmit UTOPIA
Interface block) via a standard UTOPIA Level 2
interface.
The Transmit Cell Processor will read in these cells
from the Transmit FIFO (if available) for further
processing. If no cell is available within the Trans-
mit FIFO, then the Transmit Cell Processor will
automatically generate an Idle cell. The UNI is
equipped with on-chip registers to allow for the
generation of customized Idle cells.