Problem Description

When customers dock 2M with switching, mobile and other equipment, sometimes there will be alarms of frame synchronization failure, and in the case of transmission equipment provided by our company, customers often suspect that it is a transmission problem of our company. In this case, we need to make a comprehensive judgment based on the alarms of service side equipment and transmission equipment. (There is no comprehensive document on support to locate the duplicate frame problem on 2M E1 link)

The switching equipment on the service side of both ends has alarms for frame synchronization failure, but no frame out-of-step alarms, and the docking is not successful.Transmission equipment usually has no alarms and no abnormal performance of the VC12 channel, such as BERs and pointer adjustment events.

Processing

Principle analysis of 2M link frame format related to re-framing: 2M link usually has five frame formats: PCM30, PCM31, PCM30 CRC, PCM31 CRC, and non-frame structure.

PCM30, PCM30CRC is generally used for follow-the-road signaling, 0 time slots as synchronization time slots, 16 time slots are fixed as signaling time slots and multi-frame signaling transmission, for the voice path, only the 30 time slots from 1-15 and 17-31 can be used, so it is called PCM30.

PCM31, PCM31CRC is generally used for road signaling, there is no compound frame, signaling does not have to be fixed in 16 time slots to transmit, 1-31 time slots can be all used for the voice road or all used for signaling, so it is called PCM31.

In the structure of PCM30, there is the concept of compound frame (PCM31 and non-frame structure is no compound frame), a compound frame consists of 16 subframes, recorded as F0-F15, each subframe has 32 time slots, recorded as TS0-TS31, F0 frame of the TS16 transmits the compound frame synchronization and frame out-of-sync alarm; the first four bits of four "0 The first four "0 "s are the frame positioning signals, the 5th, 7th and 8th bits are the duty bits, and if they are not used, they are set to "1", and the 6th bit is the frame out-of-step alarm indication, and if it is out-of-step, it is set to "1", and if it is synchronized, it is set to "0"; the F0 frame TS16 transmits the frame synchronization and frame out-of-step alarms. The sixth bit is the out-of-sync alarm indication, which is set to "1" for out-of-sync and "0" for synchronization;

Therefore, if the service side switching equipment has the alarm of frame synchronization failure, it is usually due to the problem of frame synchronization 8-bit group in the docking, and the two ends do not match each other. It is necessary to pay special attention to the fact that if the service side switching equipment has both the compound frame out-of-step alarm and the frame out-of-step alarm, it means that there may be a problem on the transmission side.

Solution

1, the business-side equipment appears compound frame out-of-step alarm, but there is no frame out-of-step alarm, the preliminary judgment is that the business-side switching equipment configuration errors.

2, usually, the transmission equipment will be 2M services as a net load. Checking the transmission equipment, there is no abnormal performance of VC12 transmission channel, such as BER and pointer adjustment event. Judging again, it may be the configuration error of the switching equipment on the service side.

3、If equipped with 2M BER, the 2M BER can be used to directly interface with the business-side switching equipment to check whether the 2M frame format is incorrectly configured by the relevant bytes of the 2M frame structure (for the specific byte definitions of the duplicate frames, see the description of "Cause Analysis").

4. You can also directly check whether the E1 configuration of the switching equipment at both ends, PCM30 and PCM31 are configured in the same way. If they are not consistent, since PCM31 does not carry the 8-bit group of the re-frame signal in the 16th time slot of F0 without re-framing, if the other end is configured as PCM30, the alarm of signaling re-framing synchronization failure will appear.

Remarks, usually for domestic switching equipments (including our company), E1 is configured as follow-the-road with fixed selection of PCM30, and is configured as common road with fixed configuration of PCM31. However, for equipments of foreign vendors (including E company), usually they do not configure follow-the-road, road and PCM30, PCM31 bindings, but there are other flags to control whether they are PCM31, PCM30, so when docking, you should So when docking, you should check carefully.

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. Ltd (www.opticaltrans.com), please retain! Our company specializes in Huawei SDH optical transmission equipment, SDH transmission equipment sales.