Offered Load is the traffic offered to a specific trunk group. Some of the load will be carried and some will be blocked. Thus,
offered load = carried load + blocked load (if the trunk group is a blocking one) Offered Load = Carried Load + Overflow traffic (if the trunk group does not block)
Carried Load can not be calculated, it is observed quatity (the switch management system or a data colector is resposible for pooling the data from the customer usage)
Offered Load = carried Load / (1-Blocking Factor)