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PRELIMINARY
XRT79L71
374
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
clearly convey the mode that the Receive E3 Framer block is currently operating in, Figure 174 has been
repeated below, with the "FAS Pattern Search" state shaded.
the value "[ 1,1,1,1,0,1,0,0,0,0]"). The Receive E3 Framer block will attempt to locate the FAS pattern by
performing five (5) different searches in parallel. The "FAS Pattern Search" will be declared successful if the
Receive E3 Framer block can locate a single instantiation of the FAS pattern. Once the Receive E3 Framer
block detects this particular pattern, then it will declare this instantiation of the FAS Pattern (within the incoming
E3 data-stream) as a "possible" or "candidate" FAS Pattern within the incoming E3 data-stream. Additionally,
the Receive E3 Framer block will now transition to the "FAS Pattern Verification" State, within the "E3 Frame
Acquisition/Maintenance" Algorithm (per Figure 174).
The "FAS Pattern Verification" State
Once the Receive E3 Framer block has detected the FAS Pattern, it must now verify that this pattern is indeed
the FAS pattern, and not some other set of bits within the incoming E3 data-stream (that are mimicking the FAS
pattern). Hence, the purpose of the "FAS Pattern Verification" state is to implement this additional check on the
"Candidate FAS Pattern". In order to clearly convey the mode that the Receive E3 Framer block is now
currently operating in, Figure 174 has been repeated below, with the "FAS Pattern Verification" state shaded.
FIGURE 175. THE STATE MACHINE DIAGRAM FOR THE RECEIVE E3 FRAMER BLOCK'S "FRAME ACQUISITION/MAIN-
TENANCE
" ALGORITHM (WITH THE "FAS PATTERN SEARCH STATE" SHADED)
FAS
Pattern
Search
FAS
Pattern
Search
LOF
State
LOF
State
OOF
State
OOF
State
In Frame
State
In Frame
State
FAS
Pattern
Verification
FAS
Pattern
Verification
FAS Pattern is
detected Once
FAS Pattern is
NOT Detected
FAS Patten is verified
Three consecutive times
4 Consecutive
Invalid Frames
3 Consecutive
Valid Frames
8 or 24 frame periods of
Operating in the “OOF State”
(User Selectable)
Frame Maintenance
Mode