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The multiframe framer checks for a multiframe boundary. When the multiframe framer identifies a multiframe

boundary, it updates the data path frame counters if either an OOF or OOMF condition is present. The multiframe

framer waits until a subframe boundary has been identified. Then, each bit position is checked for the multiframe

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 10-16 for the multiframe framer state diagram.

10.6.4.1.2 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. Figure 10-16 shows the multiframe framer

state diagram.

Figure 10-16. DS3 Multiframe Framer State Diagram

Sync

Load

Verify

Timeout

2 multiframe loaded

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

DS3172 Datasheet(PDF) 81 Page - Dallas Semiconductor