We daily hear bad things like CFVs, cross-border attacks, airspace violations, etc., etc. and do RR. But the thing is, we never get to hear the opposite side of the story.
So we get to hear the cases when China did something adventurous, but not when we do anything.
For airspace violations, we do it equally often, just that I think China was the first one to inaugurate the tensions in airspace for this year.
Government of India denies allegations of violation of China's airspace
www.freepressjournal.in
As for deploying S-400, it won't be effective in the mountains, and it will definitely not be effective against China which operates both S-300 and S-400 missile systems. They will know how to avoid it, if not completely run circles around it.
Short-ranged systems like Akash, SPYDER, QRSAM, Osa-AK, and AA guns will be more effective.