DS3173N datasheet(84/232 Pages) DALLAS

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Table 10-27. C-Bit DS3 Frame Overhead Bit Definitions

Bit

Definition

X1, X2

Remote Defect Indication

(RDI)

P1, P2

Parity Bits

M1, M2, and M3

Multiframe Alignment Bits

FXY

Subframe Alignment Bits

C11

Application Identification

Channel (AIC)

C12

Reserved

C13

Far-End Alarm and Control

(FEAC) signal

C21, C22, and C23

Unused

C31, C32, and C33

C-bit parity bits

C41, C42, and C43

Far-End Block Error (FEBE)

bits

C51, C52, and C53

Path Maintenance Data Link

(or HDLC) bits

C61, C62, and C63

Unused

C71, C72, and C73

Unused

X1 and X2 are the Remote Defect Indication (RDI) bits (also referred to as the far-end SEF/AIS bits). P1 and P2 are

the parity bits used for line error monitoring. M1, M2, and M3 are the multiframe alignment bits. FXY are the subframe

alignment bits. C11 is the Application Identification Channel (AIC). C12 is reserved for future network use, and has a

value of one. C13 is the Far-End Alarm and Control (FEAC) signal. C21, C22, and C23 are unused, and have a value

of one. C31, C32, and C33 are the C-bit parity bits used for path error monitoring. C41, C42, and C43 are the Far-End

Block Error (FEBE) bits used for remote path error monitoring. C51, C52, and C53 are the path maintenance data link

(or HDLC) bits. C61, C62, and C63 are unused, and have a value of one. C71, C72, and C73 are unused, and have a

value of one. The X-bit, P-bit, M-bit, C-bit, and F-bit positions are overhead bits, and the other bit positions in the

T3 frame are payload bits regardless of how they are marked by TDEN.

10.6.5.2 Transmit C-bit DS3 Frame Generation

C-bit DS3 frame generation receives the incoming payload data stream, and overwrites all of the overhead bit

locations.

The multiframe alignment bits (M1, M2, and M3) are overwritten with the values zero, one, and zero (010)

respectively.

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.

The bits C11, C12, C21, C22, C23, C61, C62, C63, C71, C72, and C73 are all overwritten with a one.

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