webrtcsink: Zero Framerate and Significant Packet Loss While Accessing Stream on Local Network

[Robert Ayrapetyan]

Hello.
I'm running a typical pipeline:
```
gst-launch-1.0 -v \
        ximagesrc display-name=$DISPLAY show-pointer=true
use-damage=false remote=true blocksize=16384 enable-navigation=true \
          ! video/x-raw,framerate=60/1 \
          ! timeoverlay \
          ! videoconvert \
          ! video/x-raw \
          ! x264enc bitrate=10000 tune=zerolatency
speed-preset=ultrafast threads=4 key-int-max=120 \
          ! video/x-h264,profile=high \
          ! queue leaky=1 \
          ! wrs. \
          pulsesrc provide-clock=true do-timestamp=true \
          ! queue leaky=1 \
          ! wrs. \
          webrtcsink name=wrs enable-data-channel-navigation=true
meta="meta,name=game-stream-cpu1" congestion-control=disabled
signaller::uri="ws://0.0.0.0:8443"
```
When accessing this stream from localhost, everything works perfectly well:
```
framesReceived/s] 60.0030
[bytesReceived_in_bits/s] 25754416.4
jitter 0
packetsLost 728
packetsReceived 5756420
```

But when trying to access the same from my home network, it becomes unusable.

Here are home network characteristics:

Server:
iperf3 -V -f m --server
```
iperf 3.9
Linux xxx 5.10.0-25-amd64 #1 SMP Debian 5.10.191-1 (2023-08-16) x86_64
-----------------------------------------------------------
Server listening on 5201
-----------------------------------------------------------
Time: Mon, 04 Sep 2023 21:23:45 GMT
Accepted connection from 192.168.1.153, port 50250
      Cookie: saapgwns5kemmgf3btdqgcinyrkstyiylki5
      Target Bitrate: 25000000
[  5] local 192.168.1.113 port 5201 connected to 192.168.1.153 port 54554
Starting Test: protocol: UDP, 1 streams, 1285 byte blocks, omitting 0
seconds, 30 second test, tos 0
[ ID] Interval           Transfer     Bitrate         Total Datagrams
[  5]   0.00-1.00   sec  2.98 MBytes  25.0 Mbits/sec  2430
...
- - - - - - - - - - - - - - - - - - - - - - - - -
Test Complete. Summary Results:
[ ID] Interval           Transfer     Bitrate         Jitter
Lost/Total Datagrams
[  5]   0.00-30.06  sec  89.6 MBytes  25.0 Mbits/sec  0.000 ms
0/73101 (0%)  sender
[  5] (receiver statistics not available)
CPU Utilization: local/sender 1.5% (1.5%u/0.0%s), remote/receiver 0.0%
(0.0%u/0.0%s)
```

Client:
iperf3 --udp -R -V -t 30 -b 25000000 --length 1285 -f m -c 192.168.1.113
```
iperf 3.14
Darwin m-w2vckv206y 22.6.0 Darwin Kernel Version 22.6.0: Wed Jul  5
22:22:05 PDT 2023; root:xnu-8796.141.3~6/RELEASE_ARM64_T6000 arm64
Control connection MSS 1448
Time: Mon, 04 Sep 2023 21:23:45 UTC
Connecting to host 192.168.1.113, port 5201
Reverse mode, remote host 192.168.1.113 is sending
      Cookie: saapgwns5kemmgf3btdqgcinyrkstyiylki5
      Target Bitrate: 25000000
[  5] local 192.168.1.153 port 54554 connected to 192.168.1.113 port 5201
Starting Test: protocol: UDP, 1 streams, 1285 byte blocks, omitting 0
seconds, 30 second test, tos 0
[ ID] Interval           Transfer     Bitrate         Jitter
Lost/Total Datagrams
[  5]   0.00-1.00   sec  3.01 MBytes  25.2 Mbits/sec  0.569 ms  0/2455 (0%)
...
- - - - - - - - - - - - - - - - - - - - - - - - -
Test Complete. Summary Results:
[ ID] Interval           Transfer     Bitrate         Jitter
Lost/Total Datagrams
[  5]   0.00-30.06  sec  89.6 MBytes  25.0 Mbits/sec  0.000 ms  0/0 (0%)  sender
[  5]   0.00-30.00  sec  89.2 MBytes  25.0 Mbits/sec  0.600 ms
162/72981 (0.22%)  receiver
iperf Done.

But WebRTC metrics on the client are following:
```
framesReceived/s] 0
[bytesReceived_in_bits/s] 19407028.4
jitter 0.016
packetsLost 451666
packetsReceived 1879638
```

I believe 0 frames issue may be attributed to packet loss, as a 24%
loss of packets can render UDP entirely impractical.

Questions:
1. Is my understanding correct?
2. Why are iperf3 results so much different?
2. How to debug/trace the reason for packet loss for WebRTC?

Thanks.