PM6344 datasheet(48/256 Pages) PMC

48 / 256 page

STANDARD PRODUCT

PMC-Sierra, Inc.

PM6344 EQUAD

PMC-951013

ISSUE 5

QUADRUPLE E1 FRAMER

These algorithms provide robust framing operation even in the presence of

random bit errors: framing with algorithm #1 or #2 provides a 99.98% probability

of finding frame alignment within 1 ms in the presence of 10-3 bit error rate and

no mimic patterns.

Once frame alignment is found, the block sets the OOF indication low, indicates a

change of frame alignment (if it occurred), and monitors the frame alignment

signal, indicating errors occurring in the 7-bit FAS pattern and in bit 2 of NFAS

frames, and indicating the debounced value of the Remote Alarm bit (bit 3 of

NFAS frames). Using debounce, the Remote Alarm bit has <0.00001%

probability of being falsely indicated in the presence of a 10-3 bit error rate. The

block declares loss of frame alignment if 3 or 4 consecutive FASs have been

received in error or, additionally, if bit 2 of NFAS frames has been in error for 3

consecutive occasions. In the presence of a random 10-3 bit error rate the frame

loss criteria provides a mean time to falsely lose frame alignment of >12 minutes.

The Frame Find Block can be forced to initiate a frame search at any time when

any of the following conditions are met:

• the software re-frame bit (REFR) in the Frame Alignment Options Register

changes from logic 0 to logic 1;

• the CRC Frame Find Block is unable to find CRC multiframe alignment; or

• the CRC Frame Find Block accumulates excessive CRC evaluation errors

(

≥ 915 CRC errors in 1 second) and is enabled to force a re-frame.

CRC Frame Find

Once the basic frame alignment has been found, the CRC Frame Find Block

searches for CRC multiframe alignment by observing whether the International

bits (bit 1 of timeslot 0) of NFAS frames follow the CRC multiframe alignment

pattern. Multiframe alignment is declared if at least two valid CRC multiframe

alignment signals are observed within 8 ms, with the time separating two

alignment signals being a multiple of 2 ms.

Once CRC multiframe alignment is found, the block sets the OOCMF indication

low, and monitors the multiframe alignment signal, indicating errors occurring in

the 6-bit pattern, and indicating the value of the FEBE bits (bit 1 of frames 13

and 15 of the multiframe).The block declares loss of CRC multiframe alignment if

four consecutive CRC multiframe alignment signals have been received in error,

or if frame alignment has been lost.

PM6344 Datasheet(PDF) 48 Page - PMC-Sierra, Inc