[eartrumpet]

What happens when the pilot is told to ascend to 36,000 or descend to 28,000? Seems like he will go through other peoples altitudes to get there.

[Joe Boucher]

Altitude encoding transponder device that tells F.A.A> radar where you are at.
Air traffic controllers will vector you at altitude, direction and rate of climb decent or stable

[Big Giant Head]

What happens when the pilot is told to ascend to 36,000 or descend to 28,000? Seems like he will go through other peoples altitudes to get there.

Any flight above 18,000 is on Instrument Flight Rules and is controlled by ATC. They're watching like the NSA, dude. They know if you're 50' off your assigned altitude. Any ascent or descent will be assigned, or approved by ATC, so there will be no conflicting traffic.