DS3173N datasheet(87/232 Pages) DALLAS

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The subframe alignment bits (FX1, FX2, FX3, and FX4) are overwritten with the values one, zero, zero, and one (1001)

respectively.

The X-bits (X1 and X2) are both overwritten with the Remote Defect Indicator (RDI). The RDI source is

programmable (automatic, 1, or 0). If the RDI is generated automatically, the X-bits are set to zero when one or

more of the indicated alarm conditions is present, and set to one when all of the indicated alarm conditions are

absent. Automatically setting RDI on LOS, SEF, LOF, or AIS is individually programmable (on or off).

The P-bits (P1 and P2) are both overwritten with the calculated payload parity from the previous DS3 frame. The

payload parity is calculated by performing modulo 2 addition of all of the payload bits after all frame processing has

been completed. P-bit generation is programmable (on or off). The P-bits will be generated if either P-bit generation

is enabled or frame generation is enabled.

If C-bit generation is enabled, the bit C11 is overwritten with an alternating one zero pattern, and all of the other C-

bits (CXY) are overwritten with zeros. If C-bit generation is disabled, then all of the C-bit timeslots (CXY) will be

treated as payload data, and passed through. C-bit generation is programmable (on or off). Note: Overhead

insertion may still overwrite the C-bit time slots even if C-bit generation is disabled.

Once all of the DS3 overhead bits have been overwritten, the data stream is passed on to error insertion. If frame

generation is disabled, the incoming DS3 signal is passed on directly to error insertion. Frame generation is

programmable (on or off). Note: P-bit generation may still be performed even if frame generation is disabled.

10.6.6.3 Transmit M23 DS3 Error Insertion

Error insertion inserts various types of errors into the different DS3 overhead bits. The types of errors that can be

inserted are framing errors and P-bit parity errors.

The framing error insertion mode is programmable (F-bit, M-bit, SEF, or OOMF). An F-bit error is a single subframe

alignment bit (FXY) error. An M-bit error is a single multiframe alignment bit (M1, M2, or M3) error. An SEF error is an

error in all the subframe alignment bits in a subframe (FX1, FX2, FX3, and FX4). An OOMF error is a single multiframe

alignment bit (M1, M2, or M3) error in each of two consecutive DS3 frames.

A P-bit parity error is generated by is inverting the value of the P-bits (P1 and P2) in a single DS3 frame. P-bit parity

error(s) can be inserted one error at a time, or continuously. The P-bit parity error insertion mode (single or

continuous) is programmable.

Each error type (framing or P-bit parity) has a separate enable. Continuous error insertion mode inserts errors at

every opportunity. Single error insertion mode inserts an error at the next opportunity when requested. The framing

multi-error insertion modes (SEF or OOMF) insert the indicated number of error(s) at the next opportunities when

requested; i.e., a single request will cause multiple errors to be inserts. The requests can be initiated by a register

bit(TSEI) or by the manual error insertion input (TMEI). The error insertion request source (register or input) is

programmable. The insertion of each particular error type is individually enabled. Once all error insertion has been

performed, the data stream is passed on to overhead insertion.

10.6.6.4 Transmit M23 DS3 Overhead Insertion

Overhead insertion can insert any (or all) of the DS3 overhead bits into the DS3 frame. The DS3 overhead bits X1,

X2, P1, P2, MX, FXY, and CXY can be sourced from the transmit overhead interface (TOHCLK, TOH, TOHEN, and

TOHSOF). The P-bits (P1 and P2) are received as an error mask (modulo 2 addition of the input bit and the

internally generated bit). The DS3 overhead insertion is fully controlled by the transmit overhead interface. If the

transmit overhead data enable signal (TOHEN) is driven high, then the bit on the transmit overhead signal (TOH) is

inserted into the output data stream. Insertion of bits using the TOH signal overwrites internal overhead insertion.

10.6.6.5 Transmit M23 DS3 AIS/Idle Generation

M23 DS3 AIS/Idle generation overwrites the data stream with AIS or an Idle signal. If transmit Idle is enabled, the

data stream payload is forced to a 1100 pattern with two ones immediately following each DS3 overhead bit. M1,

M2, and M3 bits are overwritten with the values zero, one, and zero (010) respectively. FX1, FX2, FX3, and FX4 bits are

overwritten with the values one, zero, zero, and one (1001) respectively. X1 and X2 are overwritten with 11. P1 and

P2 are overwritten with the calculated payload parity from the previous output DS3 frame. And, C31, C32, and C33

are overwritten with 000.

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