Rainbow Electronics DS3170 - Manual (Page 82)

DS3170 DS3/E3 Single-Chip Transceiver
82 of 233
boundary. The multiframe boundary is found by identifying the three multiframe alignment bits (M-bits). Since there
are seven multiframe bits and three bits are required to identify the multiframe boundary, up to 9 checks may be
needed to find the multiframe boundary. Once the multiframe boundary is identified, it is checked in each
subsequent frame. The data path frame counters are updated if the three multiframe alignment bits are error free,
and an OOF or OOMF condition exists. If the multiframe framer checks more than fifteen multiframe bit (X-bits, P-
bits, and M-bits) positions without identifying the multiframe boundary, the multiframe framer times out, and forces
the subframe framer back into the load state. Refer to
Figure 9-15 for the multiframe framer state diagram.
9.6.4.1.2 Receive DS3 Performance Monitoring
Performance monitoring checks the DS3 frame for alarm conditions and errors. The alarm conditions detected are
OOMF, OOF, SEF, LOF, COFA, LOS, AIS, Idle, RUA1, and RDI. The errors accumulated are framing, P-bit parity,
C-bit parity (C-bit format only), and Far-End Block Error (FEBE) (C-bit format only) errors.
An Out Of MultiFrame (OOMF) condition is declared when a multiframe alignment bit (M-bit) error has been
detected in two or more of the last four consecutive DS3 frames, or when a manual resynchronization is requested.
An OOMF condition is terminated when no M-bit errors have been detected in the last four consecutive DS3
frames, or when the DS3 framer updates the data path frame counters. Refer to
Figure 9-15 for the multiframe
framer state diagram.
Figure 9-15. DS3 Multiframe Framer State Diagram
Sync
Load Verify
Timeout
2 multiframe loaded
M
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its
id
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M
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it e
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tim
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ut
M
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If multiframe alignment OOF is disabled, an Out Of Frame (OOF) condition is declared when three or more out of
the last sixteen consecutive subframe alignment bits (F-bits) have been errored, or a manual resynchronization is
requested. If multiframe alignment OOF is enabled, an OOF condition is declared when three or more out of the
last sixteen consecutive F-bits have been errored, when an OOMF condition is declared, or when a manual
resynchronization is requested. If multiframe alignment OOF is disabled, an OOF condition is terminated when
none of the last sixteen consecutive F-bits has been errored, or when the DS3 framer updates the data path frame
counters. If multiframe alignment OOF is enabled, an OOF condition is terminated when an OOMF condition is not
active and none of the last sixteen consecutive F-bits has been errored, or when the DS3 framer updates the data
path frame counters. Multiframe alignment OOF is programmable (on or off).
A Severely Errored Frame (SEF) condition is declared when three or more out of the last sixteen consecutive F-bits
have been errored, or when a manual resynchronization is requested. An SEF condition is terminated when an
OOF condition is absent.