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XRT79L71
PRELIMINARY
375
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
When the Receive E3 Framer block enterse this state, it will then quit performing the "bit-by-bit" search (within
the incoming E3 data-stream) for the FAS pattern. Instead, the Receive E3 Framer block will read in a string of
10 bits that occur 1536 bits (e.g., one E3 frame period) later after the "Candidate FAS pattern" was first
detected.
The Receive E3 Framer block will perform this check during the next three (3) incoming E3 frame
periods. If, in all three of these checks, the "sampled" (or "read-in") 10-bit string matched the "FAS Pattern",
then the Receive E3 Framer block will "conclude" that it has TRULY found the FAS Pattern, and will now
transition into the "In-Frame" state. However, if (in at least one of these "10-bit pattern check"), the sampled
10-bit pattern did NOT match the "FAS Pattern", then the Receive E3 Framer block will "conclude" that it has
been fooled by data (within the incoming E3 data-stream) mimicking the FAS pattern, and will transition back
into the "FAS Pattern Search" state.
The "In-Frame" State
Once the Receive E3 Framer block (while operating in the "FAS Pattern Verification" state) detects the FAS
Pattern, in the "correct" location (e.g., exactly one E3 frame period after the "Candidate" FAS Pattern was first
detected, within three consecutive E3 frames), then it will "conclude" that it has correctly located the "FAS
Pattern" and it will transition into the "In-Frame" state. Once the Receive E3 Framer block enters the "In-
Frame" state, it will cease performing "Frame Acquisition" functions, and it will begin to perform "Frame
Maintenance" functions. A detailed description of the Receive E3 Framer block, operating in the "In-Frame"
The "OOF" (Out of Frame) State
If the Receive E3 Framer block, while operating in the "In-Frame" state, receives four (4) consecutive
"incoming" E3 frames, in which the "FAS Pattern" bits are erred, then it (the Receive E3 Framer block) will
transition into the "OOF State". In order to clearly convey the mode that the Receive E3 Framer block is
currently operating in, Figure 174 has been repeated below, with the "OOF State" shaded.
FIGURE 176. THE STATE MACHINE DIAGRAM FOR THE RECEIVE E3 FRAMER BLOCK'S "FRAME ACQUISITION/MAIN-
TENANCE
" ALGORITHM (WITH THE "FAS PATTERN VERIFICATION 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