This feature tests the communication protocol used by the agent and the server. The needed protocol requests are tested to be sure that both sides have versions of the software that are fully compatible. The protocol test also sends artificially generated data to the server and this transfer is timed.
Based on this, the maximum transfer rate can be determined. Most of the time, a value during backup of approximately 90% of this number should be seen. Generally, if you able to do a protocol test and register the workstation to the server, you are able to perform backup actions.