well, traffic is the cumulated amount of time the channels of your system have been busy.
For instance, if your system is a “cell” and you observe the traffic for 1 hour, then you might measure (for example) 10 erlangs.
It means that the cumulated time of calls in this hour = 36.000 seconds. Thus, 36.000 / 1 hour = 10 erlangs.
The TCH blocking is NOT a parameter. It is an INDICATOR.
For instance, if you measure TCH requests = 200 in one hour and TCH blocking = 4%, then it means that 4% of all requested calls were rejeted due to congestion of the TCH resources. Nb of blocked calls = 8 calls.
I hope that’s clear ?