Complex sentence: Of the 4 data channels in Physical (layer 1) and Data Link (layer 2), 1 of them is interactive, with information that depends on the contents and course of events in the messaging protocol.
Split into simpler sentences: Of the 4 data channels in Physical (layer 1) and Data Link (layer 2), 3 of them are non-interactive, and 1 of them is interactive. The information in the interactive data channel depends on the contents and course of events in the messaging protocol.