Description of the problem

Huawei OSN3500 devices can support two clock outputs, and the customer wants to utilize our transmission equipment to transmit 2Mbits clock signals over the line.

The networking platform is built as follows: ABC ring network As shown in Figure 1, A (7500) is the first node, and the external G.811 clock, B (3500) is connected to A, and C (3500) is connected to B. The clock does not form a ring, and there is no configuration protection. Standard SSM protocol is turned on for all network elements.

When the customer extracts the clock signal (120ohm 2mbits) of C (OSN3500) with its own clock device (OSILLOQUARTZ 554B B-SASE), it is not possible to get the SSM encoding, and all 5-bit bytes from SA4 to SA8 show that the signal is received. the SSU device checks the quality of the clock signal to be: ql_dnu, the quality of the signal is not available.

Processing

1, the devices have been opened standard SSM protocol, line port SSM output are working normally.

2、Check that C can normally extract the G.811 clock signal for phase-locked output.

3, The opposite end SA uses SA4 to receive SSM protocol.

4. Configure the C node to use SA4 for output.

After the above four steps are done, the customer device still cannot extract the correct clock, and it is suspected that the customer clock device also has special treatment or special definition for other SA bytes that are not used.

Contact OSILLOQUARTZ engineers to get an answer:

The device supports the extraction of any one of the bytes from SA4 to SA8, the default SA4 receives the SSM protocol, the rest of the bytes according to the ITUTG704 recommendations for 0x00 (Quality unknown), if you send a non-zero byte, the device considers that the clock signal is not available.

And our company set all the SSM bytes that are not used to 0x0f (Do not use for synchronization).

After negotiation, the terminal equipment changed the SSM configuration template, and the clock docking was completed.

Root Cause

After the terminal equipment can not detect the clock letter, you need to first determine whether our equipment SSM protocol is normal, whether the clock output phase locking is normal, whether the SA byte is normal output, and whether the terminal equipment receives in accordance with the corresponding SA byte.

1、Check the SSM configuration of the whole network.

2, check the configuration, C node configuration phase-locked line clock is normal.

3、Check the SA byte reception status of the opposite-end device.

4、Configure our device output clock.

Recommendation and summary

The ITUT Recommendation only mentions that any of the bytes from SA4 to SA8 can be used to transmit the SSM protocol, and it does not specify how the rest of the unused bytes are to be handled, so this leads to the fact that individual vendors may handle the corresponding bytes according to their own understanding of the protocol.

Therefore, when docking the clock output, not only should we consider the SSM bytes that have been used, but also whether there are any special requirements for the unused SSM bytes on the terminal equipment, which we need to take into account in the future work.

The related technical information in this chapter and the troubleshooting process of SDH equipment are collected and organized by Shenzhen Optical Transmission Network Technology Co.(www.opticaltrans.com), please retain the reproduction! Our company specializes in the sale of Huawei SDH optical transmission equipment,SDH transmission equipment.