PM6344 datasheet(49/256 Pages) PMC

49 / 256 page

STANDARD PRODUCT

PMC-Sierra, Inc.

PM6344 EQUAD

PMC-951013

ISSUE 5

QUADRUPLE E1 FRAMER

The CRC Frame Find Block will force the Frame Find Block to initiate a basic

frame search when CRC multiframe alignment has not been found for 8 ms.

CRC Check and AIS Detection

The CRC Check and AIS Detect Block computes the 4-bit CRC checksum for

each incoming sub-multiframe and compares this 4-bit result to the received

CRC remainder bits in the subsequent sub-multiframe. The block also

accumulates CRC errors over 1 second intervals, monitoring for excessive CRC

errors and optionally, forcing the Frame Find Block to initiate a frame search

when • 915 CRC errors occur in 1 second. The number of CRC errors

accumulated during the previous second is available by reading the FRMR CRC

Error Counter Registers.

The block also detects the occurrence of an unframed all-ones receive data

stream, indicating the AIS by setting the AISD indication when less than 3 zero

bits are received in 2 frames (512 consecutive bits); the AISD indication is reset

when 3 or more zeros in the E1 stream are observed, or when frame alignment is

found.

Signaling Frame Find

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

searches for CAS multiframe alignment using one of two user-selectable

algorithms, one of which is compatible with Recommendation G.732. Once

frame alignment has been found, the first algorithm monitors timeslot 16 of each

frame; it declares CAS multiframe alignment when 15 consecutive frames with

bits 1-4 of timeslot 16 not containing the alignment pattern are observed to

precede a frame with timeslot 16 containing the correct alignment pattern. The

second algorithm, compatible with G.732, also monitors timeslot 16 of each

frame, and declares CAS multiframe alignment when non-zero bits 1-4 of

timeslot 16 are observed to precede a timeslot 16 containing the correct

alignment pattern.

Once CAS multiframe alignment has been found, the block sets the OOSMF

indication to logic 0, and monitors the CAS multiframe alignment signal,

indicating errors occurring in the 4-bit pattern, and indicating the debounced

value of the remote signaling multiframe alarm bit (bit 6 of timeslot 16 of frame 0

of the multiframe). Using debounce, the remote signaling multiframe alarm bit

has < 0.00001% probability of being falsely indicated in the presence of a 10-3 bit

error rate. This block also indicates the reception of timeslot 16 AIS when

timeslot 16 has been all-ones for two consecutive frames while out of CAS

multiframe. The block declares loss of CAS multiframe alignment if two

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