Explanation: The C2 byte is used to indicate the structure and net load nature of the high-order virtual container VC-3/VC-4/VC-4-Xc.

When you view the alarm in the network management, select the alarm, and the related parameters of the alarm will be displayed in the "Alarm Details". The format of alarm parameters is "Alarm Parameters (hexadecimal): Parameter 1 Parameter 2...Parameter n". See the following table for the meaning of each parameter.

If you set the AU_AIS alarm to be forwarded when this alarm is generated, the service of this channel will be interrupted, and HP_RDI will be reported back to the opposite end station at the same time.

Note: If there is no corresponding fault phenomenon for the possible causes, or if the fault phenomenon is not listed in this section, follow the recommended order of operation in the "Processing Procedure".

The following are possible causes for the alarm HP_SLM:

• Cause 1: The service passthrough network elements are all set to overhead passthrough, and the service type of this network element is misconfigured or the C2 byte receivable is misconfigured.
• Cause 2: The service passthrough network elements are all set to overhead passthrough, and the service type of the terminating site is incorrectly configured or the C2 byte to be sent is incorrectly configured.
  Figure 1 Detection of HP_SLM Alarm 1 (Cause 1, Cause 2)
  
  
• Cause 3: The service passthrough network elements are set to overhead termination, and the service passthrough network elements should send C2 bytes incorrectly configured.
  Figure 2 Detection of HP_SLM Alarm 2
  
  

1. Query the alarm on the network management. Determine the channel number of the reported alarm according to the alarm parameters. For details, see Task Set Browsing Current Alarms for Network Elements.
2. Cause 1: The service passthrough network elements are all set to overhead passthrough, and the service type of this network element is configured incorrectly or the C2 byte receivable is configured incorrectly.
   1. Check whether the service type configured for this network element corresponds to the value of the C2 byte receivable. If they do not correspond, reconfigure the C2 byte receivable or modify the service type.
   2. Check whether the alarm is canceled. If the alarm is not eliminated, go to 3.
3. Cause 2: The service passthrough network elements are set to overhead passthrough, and the service type of the termination site is configured incorrectly or the C2 bytes to be sent are configured incorrectly.
   1. Along the direction of service flow, query upstream the network element that uploads the low-order service, and the source board of this network element is the source end that sends C2 bytes. From there, query which network element (noted as the termination site) terminates the high-order overhead and then transmits the regenerated C2 bytes to this network element. If all network elements along the way are set to overhead-through, the network element in the middle of the way transmits the C2 byte. As shown in Fig. 1, network element A is the terminating site, and network elements B and C transmit C2 bytes through.
   2. Check whether the service type configured at the terminating site corresponds to the value of the C2 byte that should be transmitted by that network element. If they do not correspond, reconfigure the C2 bytes to be sent or modify the service type according to the actual networking requirements.For the specific operation of C2 byte configuration, see Configuring C2 Bytes in the Task Set.
   3. Query whether the alarm is canceled. If the alarm is not canceled, go to 4.
4. Cause 3: The service passthrough network element sets overhead termination, and the service passthrough network element should send C2 bytes incorrectly.
   1. Along the service flow direction, check whether the overhead is set to final by the service path through the network element. As shown in Figure 2, network element A uploads a low-order service and is the terminating site. Network elements B and C penetrate the service from A to D and are the penetration sites.
   2. Depending on the actual service type, reconfigure the C2 byte of this passthrough network element or set this overhead mode to passthrough. see Task Set Configuring the C2 Byte for specific operations of C2 byte configuration. The specific operation of setting the overhead mode is as follows:
      1. Select "Service > SDH Path > SDH Path Management" in the main menu of network management. Set the filter conditions in the "Set Path Browsing Filter" dialog box that pops up, and click "Full Filter" to display the paths in the list.
      2. Select the paths you want to view, and click Maintenance > Overhead Termination. The Overhead Settings dialog box pops up.
      3. Browse the Overhead Status of the high-level path, and set it to Terminate or Pass Through, depending on your needs.
   3. Check whether the alarm is canceled. If the alarm is still not canceled, contact Huawei engineers to handle the issue.

High-order channel overhead is handled in three ways: overhead pass-through, overhead termination, and overhead detection.

Overhead Passthrough

This refers to the fact that the transmission device (this network element) only performs overhead detection on the higher-order channel overhead sent by the upstream network element without regeneration and forwards it directly to the downstream network element. In general, higher-order services (services at the VC-4 level and above) pass through higher-order overhead.

Overhead termination

means that the transmission equipment (this network element) performs overhead detection on the high-order channel overhead sent by the upstream network element and does regeneration processing, and the value of the overhead byte sent to the downstream network element is determined by the business situation of this network element. The services sent from the host side of low-order services (such as services at the VC-3 and VC-12 levels) must terminate the high-order overhead.

Overhead detection

It means that the transmission equipment (this network element) extracts the high-order channel overhead sent by the upstream network element and performs relevant processing or reports relevant alarms based on the extracted value. Overhead detection does not change the value of the high-order channel overhead.

The overhead penetration and overhead termination are shown in Figure 3.

• If the corresponding higher-order channel overhead of the eastbound line board is set to passthrough, the overhead received by the westbound line board is directly passthrough to the eastbound line board.
• If the corresponding higher order channel overhead of the eastbound line board is set to terminate, the overhead received by the westbound line board terminates at the westbound line board and regenerates at the eastbound line board.