Why do I need a second Switch to receive two streams without judder?

[MicMoba]

I have two cameras A and B. Both cameras stream a H264 over RTP. Camera A with 40Mbps and camera B with 25Mbps.

When I connect the two cameras and my display to a Switch only camera A will show. Sometimes I got a picture form camera B. When I disconnect camera A I will see the stream of camera B.

But when I connect camera A and my display to Switch 1 and camera B to Switch 2 and connect both Switch by a patch cable I can receive both streams without any judder.

I did some inverstigations. I did a record with tcpdump and analyzed it with wireshark. There I can see that RTP frames of camera B are missing when I only use one Switch.

It is independent of the Switch. I tested several Swichtes (100Mbps and 1000Mbps).

When I connect two cameras of type A or two cameras of type B to one Switch I can show their streams without any problems. It even works when the bandwith increase up to 90Mbps. I only got problems when I combine camera A with camera B.

Any ideas?

Thanks

[Yuri]

@MicMoba 
Hello,

    Perhaps the second switch provides additional buffering and this improves performance.
Please try to increase Gstreamer buffering.

Regards,
Yuri.

[MicMoba]

Hello,

thanks for reply. I put a block scheme to the attachment. My OS is a Yocto based embedded Linux. Kernel 4.14.126.

Display:

IP: 192.168.0.75

Mask: 255.255.255.0

CPU: i.MX6Quad

Ehternet: 100Mbps

Resolution: 800x480px

CAM_A:

IP:192.168.0.120

Mask: 255.255.255.0

Streaming IP: 192.168.0.75

Streaming Port: 10002

Streaming MAC: Displays MAC

Codec: H264

Streaming mode: RTP over UDP

Bitrate: 40000kbps

Resolution: 1280x800px

CAM_B:

IP:192.168.0.100

Mask: 255.255.255.0

Streaming IP: 192.168.0.75

Streaming Port: 5002

Streaming MAC: Displays MAC

Codec: H264

Streaming mode: RTP over UDP

Bitrate: 25000kbps

Resolution: 1280x800px

Switch:

I tried several Switch 10/100Mbit, 100/1000Mbit, with and without PoE support

My Script (steam2.sh):

gst-launch-1.0 -v udpsrc port=5002 ! application/x-rtp,payload=96 ! rtph264depay ! queue ! h264parse ! imxvpudec ! imxipuvideosink sync=false window-x-coord=400 window-y-coord=0 window-width=400 window-height=480 force-aspect-ratio=false &
gst-launch-1.0 -v udpsrc port=10002 ! application/x-rtp,payload=96 ! rtph264depay ! queue ! h264parse ! imxvpudec ! imxipuvideosink sync=false window-x-coord=0 window-y-coord=0 window-width=400 window-height=480 force-aspect-ratio=false

The issue is also there when I only show one stream with:

gst-launch-1.0 -v udpsrc port=5002 ! application/x-rtp,payload=96 ! rtph264depay ! queue ! h264parse ! imxvpudec ! imxipuvideosink sync=false force-aspect-ratio=false 

If I display CAM_B I will only get a picture here and there. If I display CAM_A everything is okay.

[Yuri]

MicMoba 

Hello,

  Please let me know more details about the system: block scheme, OS, (gstreamer) commands,

used to get the streams.

Regards,

Yuri.