Frame Synchronizer and Regenerative Segment Overhead Processor

This part mainly handles regenerative segment overhead related to alarms and performance events, including:

• Frame localization bytes (A1, A2)
• Regenerative segment tracking byte (J0)
• BER check byte (B1)

The alarm signaling flow is as follows:

• Optical reception

  After the STM-N optical signal from the optical path enters the optical receiving module of the circuit board, it first undergoes photoelectric conversion and is recovered into an electrical signal to be sent to the frame synchronizer and descrambler for processing. During this process, the optical conversion module will detect the signal and report the R_LOS alarm if it finds that the input signal has no light, the optical power is too low or too high, and the input signal code type does not match.

  After generating the R_LOS alarm, the system will exit the R_LOS state and enter the normal state only when the receiving optical module of this station detects two correct code patterns continuously and no new R_LOS alarm is detected at the same time.

  When R_LOS alarm occurs, the system will insert a full "1" signal to the next level circuit.

• A1, A2 and J0 Byte Detection

  When the frame synchronizer receives the STM-N signal from the optoelectronic converter module, it completes the capture of the frame positioning signal according to the A1 and A2 bytes of the signal, and at the same time extracts the line reference synchronization timing source from it, and sends it to the clock board for clock locking.

  Under normal circumstances, the A1 value is constant at F6H and the A2 value is constant at 28H, but if the wrong A1 and A2 values are detected for five consecutive frames, the R_OOF alarm will be generated. If the R_OOF alarm lasts for more than 3ms, then the frame loss alarm R_LOF is reported and an all "1" signal is inserted. In the R_LOF state, if it is in the fixed frame state again for more than 1ms, then the device returns to the normal state.

  The J0 byte is used to confirm that the two ends of the regeneration segment are in a continuous connection state, and it is required that the actual J0 and the receivable J0 on the network element match exactly; if they do not match, then the J0_MM tracking identifier mismatch alarm will be reported.

  The decoder mainly accomplishes the descrambling of other bytes in the STM-N signal except for the A1, A2 and J0 bytes and the two bytes immediately following them.

• B1 byte detection

  The regenerative segment overhead processor extracts other regenerative segment overhead bytes in the STM-N signal for processing. The most important of these is the B1 byte.

  If the B1 byte recovered from the STM-N signal does not match the BIP-8 calculation from the previous STM-N frame received, a B1 error code is reported:

  • If the B1 BER exceeds the threshold 10-6 (default value), a B1_SD alarm is generated.
  • If the B1 BER exceeds the threshold 10-3 (default value), the B1_EXC alarm is generated.

  A Regenerator Section Unavailable event is considered to have occurred when the B1 byte detects a Regenerator Section Severely Errored Second (RSSES) (30% of the error blocks in one second) after 10 consecutive seconds.

The bytes F1, D1-D3, and E1, which are not related to alarms or performance events, are sent to the master and overhead modules in this section.

Multiplexed Segment Overhead Processor

The main multiplexed segment overhead bytes related to alarms and performance events that are processed in this section are:

• Automatic protection reversal path bytes (K1, K2)
• Multiplexed segment error code monitoring byte (B2)
• Multiplexing segment remote error block indication (M1)

The alarm signal flow is as follows:

• K1, K2 byte detection

  The K2 (b6-b8) byte is used for multiplexed segment far-end failure indication:

  • If b6-b8 in K2 byte is detected to be 111, then MS_AIS alarm is reported and full "1" signal is inserted.
  • If b6 to b8 in K2 byte is 110, then MS_RDI alarm is reported.

  K1 and K2 (b1-b5) are used to transmit the APS (Automatic Protection Switching) protocol, and together with the master control unit and the crossover unit, they realize the MSP (Multiplex Section Protection) protection function.

• B2, M1 byte detection

  If the B2 byte recovered from the STM-N signal does not match the BIP-24 calculation result of the previous STM-N frame (all bits except the regeneration segment overhead), a B2 error is reported.

  It also determines whether to report the MS_REI alarm based on the M1 byte, which conveys the number of erroneous interpolated bit blocks detected by the B2 byte:

  • If the B2 BER exceeds the threshold 10-6 (default value), the B2_SD alarm is generated.
  • The B2_EXC alarm is generated if the B2 BER exceeds the threshold by 10-3 (default value).

  In the host software default state, the function of SD to initiate multiplexed segment inversion is enabled. In the case of multiplexed segment protection, the B2_SD and B2_EXC alarms trigger multiplexed segment protection inversion.

  When B2 detects a multiplexed segment severe error second MSSES for 10 consecutive seconds, a multiplexed segment unavailable second event is considered to have occurred.

Pointer Processor and Higher Order Channel Overhead Processor

This part mainly handles high-order pointer adjustment and high-order channel overhead, the bytes related to pointer adjustment are H1, H2, and H3, while the bytes related to alarm and error code include:

• Higher-order channel tracking byte (J1)
• Signal marker byte (C2)
• High-order channel error monitoring byte (B3)
• Channel status byte (G1)
• Reframe position indication byte (H4)

The alarm signal flow is as follows:

• H1, H2 detection

  The pointer processor performs pointer interpretation and pointer adjustment according to the H1 and H2 bytes of each AU-4 to accomplish the functions of frequency and phase calibration, as well as accommodating phase jitter and drift in the network, and at the same time locates each VC-4 and sends it to the corresponding high-order channel overhead processor. If the AU pointer H1 and H2 bytes are detected to be all "1's", the AU_AIS alarm is reported and the all "1's" signal is inserted. If the pointer values represented by the H1 and H2 bytes are illegal (not within the normal range of 0 to 782) and illegal pointers are received for 8 consecutive frames, the AU_LOP alarm is reported and the all "1" signal is inserted.

  If positive AU pointer adjustment occurs, the PJCHIGH count of MSA (Multiplex Section Adaptation) is increased by 1. If negative AU pointer adjustment occurs, the PJCLOW count of MSA is increased by 1.

• J1, C2, B3, G1, and H4 Byte Detection

  The Higher Order Path Overhead processor processes the Higher Order Path Overhead HPOH (Higher Order Path Overhead) bytes in the received N-way VC-4. Each of these bytes is processed as follows:

  If the J1 byte is detected to be different from the predetermined value, the HP_TIM alarm is reported and an all "1" signal is inserted.

  If the C2 byte is detected to be 00, the HP_UNEQ alarm is reported and the all "1" signal is inserted. If C2 byte is detected to be different from the predefined value, report to HP_SLM alarm and insert all "1" signals.

  Explanation:

  For Huawei Metro and OSN series devices, when HP_TIM, HP_UNEQ, and HP_SLM alarms are generated, you can choose to set whether or not to down-plug the all "1" signal on the network management, and the default is not to down-plug.

  At present, the net load structure used in our country is TUG (Tributary Unit Group) structure, and the C2 predefined value corresponding to its structure is 02.

  If the calculation result of the B3 byte recovered from the HPOH is inconsistent with the BIP-8 calculation result of the VC-4 signal of the previous frame, the B3 error code is reported.

  In STM-N (N ≤ 4) low-order SDH interface boards, the extraction of the TU-12 signal from the VC-4 requires the H4 byte to indicate that the current TU-12 is the first frame of the current complex frame. If an illegal H4 byte is detected, the HP_LOM alarm is reported.

  If b5 in byte G1 is detected to be 1, then the HP_RDI alarm is reported, and depending on whether the value of byte G1 (b1-b4) is 1-8, it is judged whether the HP_REI alarm is reported.

  When B3 detects a high-order channel severe error seconds HPSES for 10 consecutive seconds, a high-order virtual container unavailability event is considered to have occurred.

The other overhead bytes F3, K3, and N1 are reserved for use. Finally, the N-channel STM-1 net load after the above processing is sent to the cross-over board for cross-connecting the higher-order channel and the lower-order channel.