What is the difference between TCH congetion and Blocking?

What is the difference between TCH congetion and Blocking? Dear Experts, How can we diffrenciate between TCH blocking and Congetion? What is the paratmeter/unit to measure blocking and congetion? TCH Congestion = time when all resources are occupied (no free TCH available) TCH Blocking = rejected (blocked) attempts over all attempts in %. Also there is different formulas for TCH blocking. For example in subscriber perceived TCH Blocking all successful directed retries to another cell are removed from the nominator.