PM6344 datasheet(46/256 Pages) PMC

46 / 256 page

STANDARD PRODUCT

PMC-Sierra, Inc.

PM6344 EQUAD

PMC-951013

ISSUE 5

QUADRUPLE E1 FRAMER

2. Check that the FAS is absent in the following frame by verifying that bit 2 of

the assumed timeslot 0 byte is a logic 1;

3. Check that the correct 7-bit FAS is present in the assumed timeslot 0 byte of

the next frame.

If either of the conditions in steps 2 or 3 are not met, a new search for frame

alignment is initiated in the bit immediately following the errored timeslot 0 byte

location.

The second algorithm is similar to the first, but adds a one frame "hold-off" in

step 2 to begin a new search in the bit immediately following the second 7-bit

FAS that is checked. This "hold-off" is performed only after the condition in step

2 fails, providing a more robust algorithm which allows the framer to operate

correctly in the presence of fixed timeslot data imitating the FAS pattern.

A check sequence can be added to either algorithm to verify correct frame

alignment in the presence of random imitative FASs. Note that this check

sequence should be enabled when monitoring an unframed 215 -1 pseudo

random sequence to avoid framing to the single mimic framing pattern contained

in the sequence. The check consists of verifying correct frame alignment for an

additional two frames, as follows:

1. Once frame alignment (in frame "n") is determined, check that the FAS is

absent in the following frame (frame "n+1") by verifying that bit 2 of timeslot 0

is a logic 1;

2. Then, check that the correct 7-bit FAS is present in timeslot 0 of the next

frame (frame "n+2").

If either of the two conditions in the check sequence are not met, a new search

for frame alignment is initiated in the bit immediately following the errored byte

location when using the first algorithm, and is initiated in the bit immediately

following the byte location in frame "n+2" when using the second algorithm.

These algorithms are illustrated in Figure 4.

PM6344 Datasheet(PDF) 46 Page - PMC-Sierra, Inc