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Why ROS Topic should get XMLRPC address:port but ROS Service doesn't?

asked 2012-02-03 19:54:48 -0500

sam gravatar image

updated 2014-01-28 17:11:16 -0500

ngrennan gravatar image

I followed ROS Introduction (Radu Bogdan Rusu) in Events/CoTeSys-OS-School.

This is ROS Topic mechanism: image description

I can see in step 2, Listener get Talker's XML/RPC's address:port.

This is ROS Service mechanism: image description

I can see in step 2, Listener get Talker's XML/RPC's data address:port.

My question is why ROS topic should let Listener get its XML/RPC's address:port but ROS Service doesn't?

By the way:

1.what is second picture's step 3? Is step 3 is Listener making a data port connection(foo:3456) to Talker?

2.Is "foo" a IP address?

Thank you~

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answered 2012-02-04 19:56:52 -0500

ahendrix gravatar image

Publishers have an XMLRPC interface for getting the connection information, so that subscribers can request the most appropriate transport (TCP or UDP), and get an appropriate response. Since services only have one underlying transport, this extra layer is unnecessary.

1) I have no idea where step 3 went.

2) "foo" is the ROS_HOSTNAME of the machine that talker is running on. In most cases this just the machine's hostname, but it may also be a string representation of an IP.

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Is step 3 is Listener making a data port connection(foo:3456) to Talker?
sam gravatar image sam  ( 2012-02-10 12:45:07 -0500 )edit

And a little more inaccuracy in the pictures. In the first picture, in step 3, connect ("scan", TCP) should be connect ("bar", TCP). This led me to a small misconception, until I learned the original page here:

Edward gravatar image Edward  ( 2018-08-12 05:29:54 -0500 )edit

answered 2012-04-24 19:33:57 -0500

Newbee gravatar image

Please describe more detailed in first figure?

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Where do you unclear? You can question by comment.

sam gravatar image sam  ( 2012-04-26 03:45:41 -0500 )edit

Can you explain the above first figure "Topic mechanism" please?

Newbee gravatar image Newbee  ( 2012-04-30 23:24:11 -0500 )edit

Topic is used for several nodes' communication. Many nodes send different kind of messages, so the people who build ROS call it topic. The whole system can exist many topics sharing with each other.

sam gravatar image sam  ( 2012-05-01 04:06:46 -0500 )edit

@Newbee: You may want to look at the video from the presentation that accompanied those slides. . Watch both "ROS Introduction" videos by Radu B. Rusu to find the accompanying presentation segment.

Eric Perko gravatar image Eric Perko  ( 2012-05-01 06:11:25 -0500 )edit

I don't think anyone should give this thread negative point. For me, I also experience very painful on reading ros tutorials about 3 months. I think we should only give him suggestions not negative hints. Only the one who really want to do harm actions, we should give him negative hint.

sam gravatar image sam  ( 2012-05-02 07:35:01 -0500 )edit

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Asked: 2012-02-03 19:54:48 -0500

Seen: 2,372 times

Last updated: Apr 24 '12