Cannot connect to more than 2x D555 at the same time

[jingnanshi]

For our application we connect 4x D555 cameras to a PoE switch that can supply 30W per port. Each D555 individually has been tested to be able to be successfully connected and stream all RGB/depth frames. However, if we connect more than 2x D555, any additional D555 cameras cannot be detected by rs-enumerate-devices. Appreciate any help on this.

[MartyG-RealSense]

Hi @jingnanshi The D555 datasheet document states that "If multiple cameras are connected to the same switch, the data bandwidth to the host system is shared between the cameras. To achieve the best performance, a higher data speed rate switch and a host system should be considered, like a 2.5GB, 5GB or 10GB".

I also checked a RealSense white-paper guide document about using multiple D555. Whilst this document is not available publicly yet, I can quote some of its advice. When activating two or more D555 simultaneously, the 1 Gbps ethernet link can experience momentary bandwidth saturation. Even if it is briefly occurring it can overwhelm the network interface on the host, leading to packet loss.

A future firmware driver release will introduce a D555 configuration parameter called 'inter-packet delay' which when used will reduce the network load, at the expense of slower data transmission speed.

For demanding requirements (such as a high number of cameras) it may be necessary to upgrade to a 10 Gbps switch, employ traffic-shaping or QoS policies, or distribute the load across multiple NICs.

[jingnanshi]

@MartyG-RealSense After switching to a 2.5Gbp switch, I am able to stream RGB & depths from all four cameras. However, sometimes the connection to one or two of the cameras seem to be unstable (i.e., rs-enumerate-devices doesn't find all four cameras). Do you have suggestions on tuning/changing the settings on DDS to improve the performance other than waiting for the new firmware?

[MartyG-RealSense]

It is possible that a 2.5 Gbps switch is the minimum that allows 4 cameras to function but it would be more stable in future with a 5 or 10 Gbps switch.

You could try lowering the FPS speed and / or resolution to see whether it reduces network load and enables 4 cameras to function more reliably.

[jingnanshi]

@MartyG-RealSense Thanks for the response. We located the place where we are getting timeouts (at initialization): https://github.com/IntelRealSense/librealsense/blob/cacc8e701a963a44b49fe51911443797e8b3a517/third-party/realdds/src/dds-device-impl.cpp#L88.

Is there a way to configure this parameter?

[MartyG-RealSense]

You could download the source code of the librealsense SDK, edit this parameter in the dds-device-impl.cpp file and then build the modified SDK source code with CMake.

[MartyG-RealSense]

Hi @jingnanshi Do you require further assistance with this case, please? Thanks!