RELEASED
PM4354 COMET-QUAD
DATASHEET
PMC-1990315
ISSUE 6
FOUR CHANNEL COMBINED E1/T1/J1
TRANSCEIVER / FRAMER
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC. AND FOR ITS CUSTOMERS’ INTERNAL USE
44
Table 3:
- E1-FRMR Framing States
State
FAS_Find_1
NFAS_Find
FAS_Find_2
BFA
CRC to CRC Interworking
FAS_Find_1_Par
NFAS_Find_Par
FAS_Find_2_Par
BFA_Par
CRC to non-CRC Interworking
Out of Frame
Yes
Yes
Yes
No
No
No
No
No
No
No
Out of Offline Frame
No
No
No
No
No
Yes
Yes
Yes
No
No
The states of the primary basic framer and the parallel/offline framer in the E1-FRMR block at
each stage of the CRC multiframe alignment algorithm are shown in Table 3.
From an out of frame state, the E1-FRMR attempts to find basic frame alignment in accordance
with the FAS/NFAS/FAS G.706 Basic Frame Alignment procedure outlined above. Upon achieving
basic frame alignment, a 400 ms timer is started, as well as an 8 ms timer. If two CRC multiframe
alignment signals separated by a multiple of 2 ms are observed before the 8 ms timer has
expired, CRC multiframe alignment is declared.
If the 8 ms timer expires without achieving multiframe alignment, a new offline search for basic
frame alignment is initiated. This search is performed in accordance with the Basic Frame
Alignment procedure outlined above. However, this search does not immediately change the
actual basic frame alignment of the system (i.e., PCM data continues to be processed in
accordance with the first basic frame alignment found after an out of frame state while this frame
alignment search occurs as a parallel operation).
When a new basic frame alignment is found by this offline search, the 8 ms timer is restarted. If
two CRC multiframe alignment signals separated by a multiple of 2 ms are observed before the
8 ms timer has expired, CRC multiframe alignment 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.