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Transport aspects 2

15.7.2.1.2 OTU SM error detection code (BIP-8)

For section monitoring, a one-byte error detection code signal is defined in the OTU SM overhead. This byte
provides a bit interleaved parity-8 (BIP-8) code.
NOTE – The notation BIP-8 refers only to the number of BIP bits and not to the EDC usage (i.e., what quantities are
counted). For definition of BIP-8 refer to BIP-X definition in [ITU-T G.707].
The OTU BIP-8 is computed over the bits in the OPU (columns 15 to 3824) area of OTU frame i, and inserted
in the OTU BIP-8 overhead location in OTU frame i+2 (see Figure 15-14).

The OTUk contains one instance of OTU BIP-8 overhead. The OTUCn contains n instances of the OTU BIP-8
overhead, numbered 1 to n (BIP-8 #1 to BIP-8 #n).

Figure 15-14  OTU SM BIP-8 computation

15.7.2.1.3 OTU SM backward defect indication (BDI)

For section monitoring, a single-bit backward defect indication (BDI) signal is defined to convey the signal
fail status detected in a section termination sink function in the upstream direction.
BDI is set to "1" to indicate an OTU backward defect indication; otherwise, it is set to "0".

The OTUk and OTUCn contain one instance of OTU BDI overhead.
15.7.2.1.4 OTU SM backward error indication and backward incoming alignment error (BEI/BIAE)

For section monitoring, a four-bit backward error indication (BEI) and backward incoming alignment error
(BIAE) signal is defined. This signal is used to convey in the upstream direction the count of interleaved-bit
blocks that have been detected in error by the corresponding OTU section monitoring sink using the BIP-8
code. It is also used to convey in the upstream direction an incoming alignment error (IAE) condition that is
detected in the corresponding OTU section monitoring sink in the IAE overhead.

During an IAE condition the code "1011" is inserted into the BEI/BIAE field and the error count is ignored.
Otherwise the error count (0-8) is inserted into the BEI/BIAE field. The remaining six possible values
represented by these four bits can only result from some unrelated condition and shall be interpreted as
zero errors (see Table 15-1) and BIAE not active.

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