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If the SDH transmission equipment considers that the extraction and termination of the overhead byte is mainly accomplished in the high-order portion of the downstream signal flow, the main work accomplished in the upstream signal flow of that portion of the signal flow is the generation of the initial value of the overhead byte and the return of the alarm signal to the opposite end station.
Pointer Processor and Higher Order Channel Overhead Processor
The N-channel STM-1 net load signals transmitted from the cross-over board are first sent to the high-order channel overhead processor.
The high-order channel overhead processor generates the N high-order channel overhead byte and sends it to the pointer processor together with the N net load. The setup function of the high-order channel overhead bytes (including J1, C2, B3, G1, F2, F3, and N1) is completed along the upstream direction.
If the AU_AIS, AU_LOP, and HP_UNEQ alarms are detected in the downstream signal stream, b5 in the G1 byte is set to 1 and sent back to the transmitter, which reports the HP_RDI alarm. If a B3 error code is detected in the downlink signal, set b1-b4 in the G1 byte to the number of detected error blocks (1 to 8) according to the detected error code value, and send back to the transmitter the HP_REI alarm of the corresponding channel.
The H4 byte is not processed in the uplink direction.
The pointer processor generates N-way AU-4 pointers to adapt VC-4 to AU-4, where the AU-4 pointers are represented by the H1 and H2 bytes, and then the multiplexing processor multiplexes the N AU-4s into STM-N signals to the multiplexing segment overhead processor.
Multiplexing Segment Overhead Processor
The Multiplex Section Overhead Processor sets the MSOH (Multiplex Section Overhead) bytes for the received STM-N signals, including K1, K2, D4-D12, S1, M1, E2 and B2 bytes.
If an R_LOS, R_LOF, or MS_AIS alarm is detected in the downlink signal stream, b6-b8 in the K2 byte are set to 110 and the MS_RDI alarm is transmitted back to the transmitter via this byte.
If a B2 error code is detected in the downlink signal stream, the M1 byte is utilized to return an MS_REI alarm to the far end.
Frame Synchronizer and Regenerative Segment Overhead Processor
The regenerative segment overhead processor completes the setup of the regenerative segment overhead bytes, including the A1, A2, J0, E1, F1, D1-D3, and B1 bytes, and sends the complete STM-N telecommunication signal to the frame synchronizer and scrambler.
The frame synchronizer and scrambler scramble the STM-N electrical signals, and then the electro-optical conversion module converts the STM-N electrical signals into STM-N optical signals to be sent out the optical interface.
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