Yes, that's very well put. Each ATC has a specific territory in which it controls traffic.
ATC's job is to organize traffic in its area. If a plane stops talking and vanishes off ATC radar, ATC can't do anything beyond keep calling for it, alerting nearby planes, and notifying the airline it has no contact.
MH-370 vanished from both Malaysian and Vietnamese ATC radar. It stopped talking.
At that point, it was up to the pilots and the pilots alone to save the plane.
Now, entirely separately, if Thai/Malaysian military radar watchers had been more alert, maybe they could have scrambled fighter jets to try to approach the wandering plane and see what was up.
The evidence released so far says each failed to do so.
Okay, we understand that, the general idea.
Can you explain in technical terms exactly what is happening? Yes, we like details, computer code lol, break down in detail.