The berlin corridors were established during the blockade and were at heights and speeds commensurate with Yorks, Dakotas and Lancastrians of the time. These became set in concrete with a tacit agreement not to rock the boat.
The corridors were what the allies established and the Russians didn't prevent. I don't know if the agreement was then formalised.
From time to time however a corridor would be closed for dangerous air activity. This was ignored as a matter of principle and aircraft would follow the corridor track but below the corridor height.
On one such day we were in a Dominie at 4000 feet and routed directly over Mahwinkel, supposedly the largest helicopter base in Europe with over 100 hind and other types. I saw not a single helo. This pretty close to the wall coming down.