You're reading the documentation for an older, but still supported version (1.33.4).
For information on the latest version, please have a look at 1.33.5.

5.1 Robot Connection/Release

Because the robot controller and this API communicate over TCP/IP, a connection must be established first. The internal connection process includes an authentication step, so a normal connection cannot be made with other APIs or socket-related functions; use the connection-related functions of this API.

Also, when two or more robot controllers are used on one network, change the IP address of each robot controller in the T/P application so that the addresses do not overlap, and perform the connection process for each robot controller for normal control.

Because this API uses TCP/IP communication, performance degradation or functional errors in the user application can occur depending on the computer performance or the network load.

If no data is received from the controller for about 2 seconds, the connection ends and the disconnect callback is called. After a disconnect, most registered callbacks are unregistered; open_connection lists the ones that stay registered.