ROS Master

ROS is a type of middleware as explained in the previous blog post. It works as an information center. The Master is the administrator in charge of gathering data, messages, service requests and other information sent by numerous nodes, and connects them to the requested nodes. The identification between the Master and its nodes is through Master IP. Once nodes get Master’s IP and report their own ROS IP to the Master, Master doesn’t care where its nodes are physically set. They can still communicate with them. This is the unique characteristic of ROS for distributed environment.

A server is set as the home of ROS Master. Each remote robot is treated as a node to register to the Master. For example let the Master IP be 10.219.10.10 and node IP be 10.219.10.11. IP information is exported in the Master and node bashrc files individually to establish their connection.
For Master bashrc file
export ROS_MASTER_URI=10.219.10.10
export ROS_IP=10.219.10.10
For node bashrc file
export ROS_MASTER_URI=10.219.10.10
export ROS_IP=10.219.10.11
When the Master and nodes are launched, they can automatically build a connection using Master IP with each other. Hence it implements that the Master controls the node's behavior remotely.

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