XRT74L74 Datasheet, PDF (352/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
PRELIMINARY
FIGURE 143. THE STATE MACHINE DIAGRAM FOR THE RECEIVE E3 FRAMER E3 FRAME ACQUISITION/MAINTENANCE
ALGORITHM
FAS
Pattern
Search
FAS pattern is
detected once
FAS
Pattern
Verification
FAS Pattern is
not detected
LOF
Condition
FAS Pattern is
verified once
8 or 24 framing periods
of operating in the
OOF condition
(user-selectable)
OOF
Condition
3 consecutive
Valid Frames
4 consecutive
In-valid Frames
In Frame
Frame Maintenance
Mode
FIGURE 144. THE E3, ITU-T G.751 FRAMING FORMAT
1
10 11 12
Frame
Alignment
Signal
AN
384 385
768 769
1152 1153
1532
1536
Data
Data
Data
Data
BIP-4
if Selected
Framing Alignment Signal Pattern = 1111010000
When the Receive E3 Framer block detects the FAS
pattern, it will then transition over to the FAS Pattern
Verification state, per Figure 144 .
The FAS Pattern Verification State
Once the Receive E3 Framer block has detected an
“1111010000” pattern, it must verify that this pattern is
indeed the FAS pattern and not some other set of
bits, within the E3 frame, mimicking the FAS Pattern.
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