In this paper we study a single link, modelled as a loss system, that accommodates Poisson traffic originated from different service-classes. Calls of a service-class are distinguished to new and handover calls. New calls compete for the available link bandwidth under a threshold call admission policy. In this policy, new calls of a service-class are not allowed to enter the system if the number of in-service new and handover calls of the same service-class plus the new call, exceeds a threshold (different for each service-class). On the other hand, handover calls compete for the available link bandwidth under the complete sharing policy. The steady state probabilities in this model have a Product Form Solution (PFS). Due to the existence of a PFS, a convolution algorithm is proposed for the accurate calculation of call blocking probabilities and link utilization.