The call-level QoS assessment in ATM networks remains an open issue, due to elastic services. We consider the coexistence of ABR services with QoS guarantee services in a VP link and evaluate the call blocking probabilities (CBP). To this end, firstly, we review two extensions of the Erlang Multirate Loss Model and examine their applicability on ABR services. In the first extension, the retry models, blocked calls can retry with reduced resource requirements and increased arbitrary mean

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... y requirements. In the second extension, the threshold models, request sizes and residency times are state dependent. For both models, we present expressions for efficient calculation of the final CBP. Secondly, we propose the connection-dependent threshold model, which resembles the threshold models, but the state dependency is individualized among call connections. Finally we evaluate the above-mentioned models by comparing them based on the resultant CBP. Our investigation shows that the retry models can hardly approach the behavior of ABR services, while the threshold models perform better than the retry models. The proposed connection-dependent threshold model performs much better than the threshold models. Simulation results validate the proposed model.