How to investigate Discard in Upstream GPON port?

Issue Description

We spot the amount of “Discarded Traffic” is directly proportional to the amount of traffic.
We didn’t evaluate the impact on our service, this is why I’m doing this investigation is to know what is discarded.
Since we don’t know what is discarded, we will not ignore this.
I setup a scenario where I want to capture traffic behind ONT on LAN and I would like to capture the Ethernet traffic going inside the GPON port.
I tried the following command, no success.

fn04.lab001.bb(config)#mirror port src-port 0/0/4  dst-port 0/6/2 ingress

Failure:
The port is not an ETH port
How can I mirror the Ethernet traffic in GPON port? Is there a way?
My goal is to capture the traffic sent by our STB and compare it with the one on the GPON port.

Solution

Generally, you can use the following commands to get more information about the statistics about service-port:

huawei(config)#start statistics service-port [index] //for each service-port on the port
//reproduce the issue (find some discard on the port)
huawei(config)#display statistics service-port [index ] //try to find if any discard statistics on the service-port
huawei(config)#stop statistics service-port [index]
The service-port capture can be used to packet header obtaining on each service-port on the port:
//start the capture
MA5600T(diagnose)%%file-server auto-backup board-info primary [server-ip] tftp   //you can choose ftp
MA5600T(diagnose)%%capture service-port [srvid] capture-count 1000000 capture-time 2000
 //reproduce the issue
// undo the capture
MA5600T(diagnose)%%undo capture service-port
MA5680T(diagnose)%%undo file-server auto-backup board-info primary