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The frequency deviation threshold of the TN52TQX is set to a low value, and therefore a large number of bit errors occur in a 10GE LAN service

Publication Date:  2012-07-25 Views:  51 Downloads:  0
Issue Description
A user requires that an end-to-en 10GE LAN service be configured between the TN52TQX housed in slot 7 at site A and the TN52TQX housed in slot 5 at site B. The Data Service Center reports that bit errors transiently occur in the service, and the service is unavailable.
Version information:
OptiX OSN 8800 V100R002C00SPC400 (5.51.05.23)
T2100 V200R002C01SPC003
Alarm Information
When the client-side optical interface on the TN52TQX board at one end accesses a 10GE LAN service from a router, the ODU2_PM_BDI alarm is transiently reported.
Handling Process

1.         Check service access at site B.
After an inloop is performed at the client-side optical interface of the TN52TQX at site A, the service is normal and no alarm is reported. This indicates that the equipment fault is not caused by a service access fault or a fault of the line board at site A. Hence, the fault is probably located at a place between the TN52TQX housed at site A and the router.

2.         Locate the fault at site A.
After a cross-connect loopback is performed on the TN52TQX housed in slot 7 at site A, the board reports the ODU2_PM_BDI alarm. After querying the alarm information on the internal register of the board, Huawei engineers detect that the frequency deviation of the service accessed by the board exceeds the frequency deviation threshold when the TN52TQX board is in BIT transparent transmission mode. When the frequency deviation of the service accessed by the board exceeds the set threshold, a large number of bit errors occur. As a result, the board reports the ODU2_PM_BDI alarm.

3.         Analyze and verify the conclusion, and modify the configuration to avoid this problem.
Based on the preceding problem locating and analysis, Huawei engineers determine that this problem occurs because the frequency deviation of the accessed service exceeds the frequency deviation threshold (the current threshold is 20�30 ppm) when the TN52TQX is in BIT transparent transmission mode. As a result, the board reports the ODU2_PM_BDI alarm.
The TN52TQX in 10GE LAN MAC transparent transmission mode can tolerate the frequency deviation of the accessed service in a certain range. After setting the TN52TQX boards at site A and site B to the 10GE LAN MAC transparent transmission mode, Huawei engineers detect that the alarm disappears, no bit error occurs, and the service is restored. When ping packets are transmitted between the two sites for a long time, no packet is lost. Hence, Huawei engineers determine that this problem occurs because the frequency deviation of the service from the router exceeds the frequency deviation when the TN52TQX is in 10GE LAN BIT transparent transmission mode.

Root Cause
Based on the onsite situation, Huawei engineers determine that the alarm is reported when the TN52TQX accesses the 10GE LAN service, but the alarm disappears when the TN52TQX accesses no service. This situation indicates that transient reporting of the ODU2_PM_BDI alarm is associated with the service, and therefore Huawei engineers need to check the client-side services on the two sides.
Suggestions
1. According to the associated international standard, frequency deviation of a 10GE LAN service must reach 100 ppm, but the current frequency deviation of a service accessed by the TN52TQX is within the range of 20�30 ppm. The problem will be solved in a version, which will be released later.
2. The 10GE LAN service can be configured to the 10GE LAN MAC transparent transmission mode (10.7G) or 10GE LAN BIT transparent transmission mode (11.1G). The differences between the preceding two modes are as follows:
a. 10GE LAN MAC transparent transmission mode
After GFP-F encapsulation is performed on 10GE LAN signals, the signals are mapped to standard OTU2 frames. In this manner, client 10GE MAC frames are transparently transmitted. In this mode, services are in standard OTU2 frames and the transmission rate is 10.71 Gbit/s. Therefore, the services can be transmitted by all equipment that supports the standard rate specified in the protocol.
b. 10G ELAN BIT transparent transmission mode
In 10GE LAN BIT transparent transmission mode, client-side services are directly mapped to OTU2 frames, and the services are transmitted by increasing OTU2 frame frequency. The service rate is 11.1 Gbit/s, which is higher than the standard rate of OTU2 signals.
c. When the LINK information is transparently transmitted along with client-side services, the TN52TQX must be configured in 10GE LAN MAC transparent transmission + LPT enable mode or BIT transparent transmission mode.

END