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Bandwith use of ros topic

asked 2012-03-27 15:35:18 -0500

NsN gravatar image

updated 2012-03-27 17:41:11 -0500

joq gravatar image

Hi, I'm going to run my ros system on multiple computers, connected only by a wifi link of (possibly) bad quality. However I want to use data from multiple usb web cams.

I'm wondering how ros distributes the various message on the network and if it makes a difference where roscore is located.

Example Scenario:

Machine 1:
  Node 1:
    outgoing topics:
      camera1/image_raw
      camera1/image_compressed

Machine 2:
  Node 2:
    outgoing topics:
      camera2/image_raw
      camera2/image_compressed

Machine 3:
  Node 3.1:
    incoming topics:
      camera1/image_raw
      camera2/image_raw
    outgoing topics:
      control/steering
      control/debug

  Node 3.1:
    incoming topics:
      camera1/image_raw
      control/steering

1) Which messages are actually send?

2) Do the camera*/image_compressed topics take up bandwith, even though they are never subscribed to?

3) is camera1/image_raw send twice over the network?

4) is camera2/image_raw also send to machine 1?

5) Does it matter whether roscore is started on machine 1 or machine 3?

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answered 2012-03-27 17:39:43 -0500

joq gravatar image

Each message is sent pairwise over a TCP connection, directly from the publisher to each subscriber.

1) Messages that are actually subscribed

2) No.

3) Yes. I believe there are ways to avoid that.

4) No.

5) Mostly not.

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Re 3): You can use http://www.ros.org/wiki/topic_tools/relay on machine 3 to have a local node that republishes the incoming images, so that other local nodes can subscribe to that relay instead of the topic published by machine 1.

Stephan gravatar image Stephan  ( 2012-03-27 23:36:16 -0500 )edit

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Asked: 2012-03-27 15:35:18 -0500

Seen: 531 times

Last updated: Mar 27 '12