9 Replies Latest reply on Feb 16, 2018 12:50 PM by BjarneG

    USB bandwidth and connections

    fred_dev

      I have a question about the realsense physican connector on the D400 series (I am looking at the D435 camera). I see it is a USB C (usb 3.1) connector, but the specs page says that is USB 3.0 Type - C. is this just a typo, or does the camera run on usb 3.0 (meaning a 5 ghz bandwidth).

       

      Does the camera developer kit come with any bundled cables? USB C to USB type A cables are available, as I have USB 3.0 ports, if the spec is correct I should be able to use these ports for the camera. If I use a USB 3.1 connection do I get access to any higher features (the 90 fps seems a lot for USB 3.0) ?

       

      I also do not see any power requirements on the specifications, USB 3.1 can provide more current, (usb 3.0 has 1.5 amps and 3.1 is up to 5 amps), it would be great to know the requirements for the cameras.

       

      I am asking this also as I am looking at the cameras to replace kinect V2 cameras, I have high quality USB 3.0 cables that are 5m long that allow me to use kinect V2 cameras at full 5gpps. I dont find many usb 3.0 to usb c cables, mostly charging cables for phones that dont support data, or full data rates, I am happy to make a custom convertor for myself if I know the actual specs.

       

      What cables are people using with the D435? Has anyone extended the distance between the camera and the computer?

       

      I know I can use remote computers and retreive the data over a network but I am trying to avoid this for various reasons.

       

      Thanks for your time.

       

      Fred

        • 1. Re: USB bandwidth and connections
          MartyG

          USB Type-C is just the technical name for USB-C.  The 400 Series cameras are designed to use USB 3.0.

           

          RealSense USB cameras always come bundled with the USB cable.

           

          I am not aware of any speed advantage gained by using the camera in a USB 3.1 port.

           

          The camera is powered through VBUS power of the USB port and requires 5v.  The Vision Processor D4 component in turn powers the depth module.  You can read the camera's full technical specifications in its data sheet document.

           

          https://software.intel.com/sites/default/files/Intel_RealSense_Depth_Cam_D400_Series_Datasheet.pdf

           

          Long extension cables do not typically work well with RealSense cameras due to the huge volume of camera data that is passed through the cable, using up the bandwidth.  Even with high quality premium grade cables, the camera has usually not worked with cables longer than 2 m.  There has been suggestion that optical USB cables may extend this range, but this is unverified by Intel lab testing.

           

          The 400 Series cameras have not been available for long enough yet for cable recommendations to have been offered by the community, unfortunately.  It is possible that someone may provide feedback as a result of seeing your message.

          • 2. Re: USB bandwidth and connections
            fred_dev

            This company claims these cables will work with the d series cameras.

             

            NTC | USB 3.1 Gen 2 A Male to C Male Cables

            • 3. Re: USB bandwidth and connections
              MartyG

              My opinion is that unless you purchased the highest grade cable possible then you risk the camera not working at cable lengths over 2 m.   Even with a top-end cable there would be few guarantees.  In over three years of supporting RealSense, I have never come across a person who has been able to make RealSense cameras work with cables longer than 2 m.  If it were possible then there probably would have been some reported cases of success by now.

              • 4. Re: USB bandwidth and connections
                BjarneG

                Fwiw, we are successfully using "active" USB 3.0 cables to extend the 1m cable shipped with the D435-cameras. Works nicely, even with two and three cameras.

                 

                My apologies for hijacking the thread, but I noticed that "bandwidth" is mentioned in the original post: Are there any guidelines or best-practices for calculating the USB bandwidth-requirements of the D400-cameras? (I know how to calculate size of a frame and multiply this by framerate - I am interested in actual/real-life bandwidth, including protocol-overhead, when streaming depth and rgb.)

                 

                Ultimately, we want to drive multiple D435 from a single host and it is useful to be able to understand and estimate this limitation.

                 

                Regards,

                - Bjarne

                • 5. Re: USB bandwidth and connections
                  MartyG

                  I could not find any formal processes for calculating the USB bandwidth of RealSense cameras, unfortunately.  As a general rule of thumb though, bandwidth is related to resolution.  The lower the resolution being used, the less bandwidth that should be used.  The opposite is true for using high resolution.

                   

                  One of the leaders of Librealsense, Dorodnic, also had this advice in 2016 about multi-camera use in Librealsense: "Using the same USB3 controller for more then one RealSense device is not recommended.  Bandwidth of USB3 is limited and you will inevitably lose frames.  If you're using separate USB controllers, you will still need a powerful PC or you will have frame drops at the kernel driver level."

                  • 6. Re: USB bandwidth and connections
                    BjarneG

                    Thanks, MartyG.

                     

                    I have tested up to four cameras on a single Intel NUC running Ubuntu 16.04. The total amount of image-data must be limited by reducing resolution, framerate and channels (grayscale instead of color), but it does work without losing too many frames. I connected the cams via two separately powered USB-hubs (NUC shuts down otherwise) but I'm still rather impressed by the fact that this works when running the realsense-viewer.

                     

                    Would anyone from Intel like to comment on Dorodnics advice from 2016? Does this still apply? Have you done any benchmarking in this direction? Any clues to amount of overhead in the protocol?

                     

                    Regards,

                    - Bjarne

                     

                    • 7. Re: USB bandwidth and connections
                      Newnex

                      USB 3.1 Gen 1 and USB 3.0 are basically the same thing. In another word, D400 series is using USB 3.0 connectivity with a Type-C interface. The USB 3.0 (or 3.1 Gen 1) Type-A to Type-C cable is basically the same thing to USB 3.0 A to micro B cable that you use for 200 series RealSense Camera.

                       

                      Regarding your bandwidth concern, as long as the USB cable you use meets the signal integrity standard, shouldn't be a problem work with the camera.

                      Just make sure you don't share multiple cameras by one upstream USB 3.0 hub. Sharing cameras directly connect to your CPU is fine though, the main bus designed to support multiple full bandwidth USB 3.0 lines.

                       

                      3m and 5m industrial grade USB 3.0 cable has been widely used by industrial applications such as machine vision, medical imaging for many years. These applications also require high bandwidth and frame rate transmission as well as RealSense.

                      https://www.newnex.com/usb-cable-maximum-length-limits.php

                      Hope this white paper can help a bit.

                      • 8. Re: USB bandwidth and connections
                        Intel Corporation
                        This message was posted on behalf of Intel Corporation

                        Hello BjarneG, 

                        Thanks for your interest in the Intel® RealSense Technology.

                        Intel will soon publish a white paper that contains all the information regarding USB bandwidth requirements for the D400 series cameras. 

                        We don't have a publication date yet. We will post a blog on this community when it is available.

                        Thank you for your patience and understanding.

                        Best regards,

                        Josh B.
                        Intel Customer Support

                        • 9. Re: USB bandwidth and connections
                          BjarneG

                          @Newnex: Thanks for info!

                           

                          @Josh B: Looking fwd to reading the whitepaper.

                           

                          Regards,

                          - Bjarne