STANDARD PRODUCT
PM4328 TECT3
DATASHEET
PMC-2011596
ISSUE 1
HIGH DENSITY T1/E1 FRAMER
AND M13 MULTIPLEXER
time of 1 ms. In DS2 mode, both the F-bits and M-bits must be correct for a
significant period of time before frame alignment is declared. In G.747 mode,
frame alignment is declared if the candidate frame alignment signal has been
correct for 3 consecutive frames (in accordance with CCITT Rec. G.747 Section
4). Once in frame, the DS2 FRMR provides indications of the M-frame and M-
subframe boundaries, and identifies the overhead bit positions in the incoming
DS2 signal or provides indications of the frame boundaries and overhead bit
positions in the incoming G.747 signal.
Depending on configuration, declaration of DS2 out-of-frame occurs when 2 out
of 4 or 2 out of 5 consecutive F-bits are in error (These two ratios are
recommended in TR-TSY-000009 Section 4.1.2) or when one or more M-bit
errors are detected in 3 out of 4 consecutive M-frames. The M-bit error criteria
for OOF can be disabled via the MBDIS bit in the DS2 Framer configuration
register. In G.747 mode, out-of-frame is declared when four consecutive frame
alignment signals are incorrectly received (in accordance with CCITT Rec. G.747
Section 4). Note that the DS2 framer is an off-line framer, indicating both OFF
and COFA. Error events continue to be indicated even when the FRMR is
indicating OOF, based on the previous frame alignment.
The RED alarm and alarm indication signal are detected by the DS2 FRMR in
9.9 ms for DS2 format and in 6.9 ms for G.747 format. The framer employs a
simple integration algorithm (with a 1:1 slope) that is based on the occurrence of
"valid" DS2 M-frame or G.747 frame intervals. For the RED alarm, a DS2 M-
frame (or G.747 frame, depending upon the framing format selected) is said to
be a "valid" interval if it contains a RED defect, defined as the occurrence of an
OOF event during that M-frame (or G.747 frame). For AIS, a DS2 M-frame (or
G.747 frame) is said to be a "valid" interval if it contains AIS, defined as the
occurrence of less than 9 zeros while the framer is out of frame during that M-
frame (or G.747 frame). The discrepancy threshold ensures the detection
algorithm operates in the presence of bit error rates of up to 10-3. Each "valid"
DS2 M-frame (or G.747 frame) causes an integration counter to increment; "non-
valid" DS2 M-frame (or G.747 frame) intervals cause a decrement. RED or AIS
is declared if the associated integrator count saturates at 53, resulting in a
detection time of 9.9 ms for DS2 and 6.9 ms for G.747. RED or AIS declaration
is deasserted when the associated count decrements to 0.
The DS2 X-bit or G.747 remote alarm indication (RAI) bit is extracted by the DS2
FRMR to provide an indication of far end receive failure. The FERF status is set
to the current X/RAI state only if the two successive X/RAI bits were in the same
state. The extracted FERF status is buffered for 6 DS2 M-frames or 6 G.747
frames before being reported within the DS2 FRMR Status register. This buffer
ensures a virtually 100% probability of freezing the FERF status in a valid state
during an out of frame occurrence in DS2 mode, and ensures a better than
99.9% probability of freezing the valid status during an OOF occurrence in G.747
PROPRIETARY AND CONFIDENTIAL
83
PMC [ PMC-SIERRA, INC ]
