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Knowledge Base

Unilateral picture freeze and timing picture refresh in 8020 terminals when interconnecting with V MCU

Publication Date:  2019-07-23  |   Views:  250  |   Downloads:  0  |   Author:  wangjingyang  |   Document ID:  EKB1000015755


Issue Description

Satellite V35 network, RS449 interface, 768kbps rate. MCU of V company is satellite device of a foreign company. Terminal are 8020, V Company and P Company.  
Failure description:
1. At a conference site with 8020 terminals, picture received from other terminals of MCU side is normal. Picture receive from 8020 site by MCU side is obviously refreshed every seconds, with critical freeze and pixilation phenomenon.
2. Other 8020 terminals joined in conference have same faults at different degrees with only picture refresh and no picture freeze.
3. Audio signal is normal.
4. 8020 and V‘s devices at MCU side are all connected to satellite and normal, no picture fault.
5. Editions of 8020s is the same, old devices in MCU side of satellite. Satellite devices in 8020 deployment site are new delivered.

Alarm Information

Unilateral and slight bit error in satellite NM, and bit error accrued.

Handling Process

1. Check 8020 configuration and capability set configuration about interconnect with MCU. All is OK.
Check terminal software edition, equipment room environment, power supply and earth wire, some sites is unqualified. After remold, the fault remains.
2. Some terminal test is completed and no fault. By local digital loopback, terminal is normal. Far end digital loopback, MCU side digital loopback, the picture is abnormal. The failure cause may be on unilateral line. Terminal failure is still possible, because signal sent maybe incorrect.
3. Transmission lines inspection, antenna gain inadequate, CNR is relative low. Adjust the antenna again, the fault remain.
4. Replace IDU devices, the fault remains.
5. Replace 8020 terminal, the fault remains.
6. Replace 8020 software, the fault remains.
7. Check if the V35 interface signals the same as MCU joint signal. Clock is slight shift, but fundamentally normal. Check voltage of signal earth and protection earth.
8. Do hardware loopback with V35 ports at terminal side. Connect local end directly to far end. Picture received in far end is its own picture which is sent and loopback from local end. Fault phenomenon emerges. So this phenomenon is irrelevant with terminal.
9. Do software modification test and change a parameter to make terminal not response to MCU refresh command. Test again, the fault phenomenon disappear. It is MCU side that sends refresh command timely. Short refresh period make fault happen. Why MCU send refresh command frequently. The cause may be bit error in lines or problem in MCU.
10. Considering best compatibility with V's MCU, replace 8020 with V, the fault remains. V's terminal has been interconnected with MCU for over a year. So this failure is irrelative with Huawei terminal.
11. The cause must be the connection lines. IDU device is the most possible cause. Test with a well IDU borrowed from another place, the picture become normal. The IDU replaced before is also unqualified. IDU of this lot are all unqualified.
12. Test conference site terminals in another company with IDU of this lot, same fault appear. So the failure cause is IDU device.

Root Cause

Early and new delivered Satellite IDU devices are different in lots. New lot devices has quality problem. The handing process twists because of complex circumstance, commissioning measures and customer cognitive ability.