STANDARD PRODUCT
PM4351 COMET
DATA SHEET
PMC-1970624
ISSUE 10
COMBINED E1/T1 TRANSCEIVER
is declared and the basic frame alignment is set accordingly (i.e., the basic frame
alignment is set to correspond to the frame alignment found by the parallel offline
search, which is also the basic frame alignment corresponding to the newly
found CRC multiframe alignment).
Subsequent expirations of the 8 ms timer will likewise reinitiate a new search for
basic frame alignment. If, however, the 400 ms timer expires at any time during
this procedure, the E1-FRMR stops searching for CRC multiframe alignment and
declares CRC-to-non-CRC interworking. In this mode, the E1-FRMR may be
optionally set to either halt searching for CRC multiframe altogether, or may
continue searching for CRC multiframe alignment using the established basic
frame alignment. In either case, no further adjustments are made to the basic
frame alignment, and no offline searches for basic frame alignment occur once
CRC-to-non-CRC interworking is declared: it is assumed that the established
basic frame alignment at this point is correct.
AIS Detection
When an unframed all-ones receive data stream is received, an AIS defect is
indicated by setting the AISD bit to logic 1 when fewer than three zero bits are
received in 512 consecutive bits or, optionally, in each of two consecutive periods
of 512 bits. The AISD bit is reset to logic 0 when three or more zeros in 512
consecutive bits or in each of two consecutive periods of 512 bits. Finding frame
alignment will also cause the AISD bit to be set to logic 0.
Signaling Frame Alignment
Once the basic frame alignment has been found, the E1-FRMR searches for
Channel Associated Signaling (CAS) multiframe alignment using the following
G.732 compliant algorithm: signaling multiframe alignment is declared when at
least one non-zero time slot 16 bit is observed to precede a time slot 16
containing the correct CAS alignment pattern, namely four zeros (“0000”) in the
first four bit positions of timeslot 16.
Once signaling multiframe alignment has been found, the E1-FRMR sets the
OOSMFV bit of the E1-FRMR Framing Status register to logic 0, and monitors
the signaling 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
-3
falsely indicated in the presence of a 10 bit error rate.
The block declares loss of CAS multiframe alignment if two consecutive CAS
multiframe alignment signals have been received in error, or additionally, if all the
bits in time slot 16 are logic 0 for 1 or 2 (selectable) CAS multiframes. Loss of
PROPRIETARY AND CONFIDENTIAL
45
PMC [ PMC-SIERRA, INC ]
