ryu-manager runs the Python programs written for Ryu. The --verbose flag prints more detailed logs to the console. The --observe-links flag observes link discovery events.

By running,

$ ryu-manager -help

you may find brief information about all the flags of ryu-manager.

wscat (node-ws) is a web socket listener based on Node.js. When Mininet joins, it triggers an event of change in links, as an EventLinkAdd event. This is reported and logged in the wscat. Similarly, we can also listen to the other changes in the topology, including addition and deletion of switches and addition of hosts to the topology.