XRT74L73 Datasheet, PDF (138/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
TABLE 23: BYTE-FORMAT OF THE PLCP FRAME
PLCP FRAME
2 BYTES
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
A1
A2
POI
1 BYTE
P11
P10
P9
P8
P7
P6
P5
P4
P3
P2
P1
P0
POH
1 BYTE
Z6
Z5
Z4
Z3
Z2
Z1
X
B1
G1
X
X
C1
PLCP PAYLOAD
53 BYTES
First ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
ATM Cell
Twelfth ATM Cell
13–14 nibbles
Trailer
3.3.2.1.2Cell Delineation while the UNI is Operat-
ing in the “Direct-Mapped ATM”
mode.
When the UNI is operating in the “Direct-Mapped
ATM” mode, then the Receive Cell Processor is
receiving unframed cell data from the Receive DS3
Framer. Therefore, the Receive Cell Processor will
have to use the “HEC Byte” Cell-Delineation algo-
rithm in order to locate the boundaries of these cells.
The HEC Byte Cell Delineation algorithm contains
three states: HUNT, PRESYNC, and SYNC, as
depicted in the State Machine Diagram in Figure 29 .
Each of these states are discussed below. .
FIGURE 29. CELL DELINEATION ALGORITHM EMPLOYED BY THE RECEIVE CELL PROCESSOR, WHEN THE UNI IS
OPERATING IN THE “DIRECT-MAPPED” ATM MODE.
HUNT
Correct HEC
Incorrect HEC
PRESYNC
ALPHA Consecutive
Incorrect HEC
SYNC
DELTA Consecutive Correct
HEC at 53 Byte Intervals
The HUNT State
When the UNI chip is first powered up and configured
to operate in the “Direct-Mapped ATM” mode, the
Receive Cell Processor will initially be operating in
the “HUNT” state. While the Receive Cell Processor
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