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Latency between nodes

asked 2022-04-12 09:00:47 -0500

risbo6 gravatar image

updated 2022-04-12 09:01:18 -0500

Hey,

Let's imagine that I have the following three nodes :

  1. Nodes A and B are running on machine 1.
  2. Node C is running on machine 2 (Roscore runs on machine 2).

Machines 1 and 2 are on the same ROS network . If you ping machine 2 from machine 1, you'll get around 50 ms of delay.

My question is pretty simple, what will be the delay if node A is communicating with node B ? Will it be less than 50 ms since both nodes are running on the same machine or will it go through machine 2 ?

Cheers

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answered 2022-04-12 09:22:41 -0500

FurkanEdizkan gravatar image

updated 2022-04-14 04:56:01 -0500

I can't answer correctly what will happen to the delay, but every ROS message has a timestamp attached to it. So maybe you could try to send a dummy message and compare the timestamps of sent and received messages. Maybe look into the this answer. Hope it helps!

Edit1: As far as I know it should work similar to image below, If I am wrong please tell me.

Edit2: So, roscore registers all to all but communication between nodes/messages are directly connected. image description

Here are some links that could help

https://atlas-itn.eu/wp-content/uploads/2021/10/ROS_multiple_machine_final.pdf

http://wiki.ros.org/ROS/Tutorials/MultipleMachines

http://wiki.ros.org/ROS/NetworkSetup

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Comments

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The ROS Master is not involved in communication between nodes. They are all peer-to-peer. So for nodes "on the same machine", they will have a direct connection. For nodes on different machines, they will also open direct connections.

In your diagram, node 2-1 would open a direct connection to node 3-1. There would be no traffic through Computer 1 Roscore.

I don't have the possibility to do it myself, but please search ROS Answers for previous Q&As about this topic. There have been a few. Use Google and append site:answers.ros.org to your search query.

gvdhoorn gravatar image gvdhoorn  ( 2022-04-13 14:52:28 -0500 )edit

I did some research and edit my answer again hope this time it is correct, thank you!

FurkanEdizkan gravatar image FurkanEdizkan  ( 2022-04-14 02:54:01 -0500 )edit

I'm not seeing anything different.

Your diagram still implies communication between Node 2-1 and Node 3-1 would be "routed through" the ROS Master on Computer 1.

gvdhoorn gravatar image gvdhoorn  ( 2022-04-14 03:59:42 -0500 )edit

Should have deleted first picture, my bad

FurkanEdizkan gravatar image FurkanEdizkan  ( 2022-04-14 04:53:29 -0500 )edit

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Asked: 2022-04-12 09:00:47 -0500

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Last updated: Apr 14 '22