Domina M,
I don't think that you are splitting hairs, I think the two concepts are very much different. To me, protocol is the nearly effortless exhibition of well trained behavior by the submissive in a non-session environment. This requires an acute and consistent awareness of the Mistress's expectations. For example, the sub might be expected to maintain a specific position relative to the Domme while walking with her. Or focusing on her so that when she slightly nods to her nearly empty wine glass he moves quickly to get another. Perhaps a set of protocols that are in place while cooking and serving a meal to her. I've been in two relationships where adherence to these and other protocols was expected, but they were by no means constantly in place. That would have been exhausting and more like work than the erotic, sexy BDSM that we both so enjoyed. They were the exception to the rule for most of our time together, but when she was in "THAT" mood I was expected to be on my game and not disappoint her. I had two such personal relationships.

To me ritual is session focused. A ritual of relaxed conversation before a session starts is a great way to settle the nerves and to begin to let your mind slip to that wonderful submissive or dominant mindset. Kneeling to start a session, kneeling while facing a corner when the Domme leaves the room, or kneeling with head down touching the floor, counting strokes in a certain trained fashion. Perhaps undressing in a certain way. These are all examples of ritual that I have experienced.

I think protocol is rarely experienced on the typical professional session due to time constraints and the dynamics of "most" sessions, Ialso beleive that ritual is best established with a truly professional Domme over some extended period of time spent together in session.