Two Level Scheduling Algorithm (TLSA) is a QoS-enabled fair and efficient connection admission control and packet scheduling algorithm for WiMAX networks. At the first level, an inter-class scheduling algorithm distributes bandwidth among various WiMAX service classes. Then at the second level, class specific algorithms distribute bandwidth among connections of the associated class. The present paper focuses on a Markov chain based analytical model of TLSA that is comprehensive enough to depict the behavior of inter-class and intra-class scheduling algorithms. Extensive simulations were performed and several criteria were considered to assess the accuracy of the proposed model. We considered bandwidth allocation in both inter-class and intra-class scheduling algorithms, percentage of lost packets and the service ratio. The experiments indicate that the analytical model faithfully captures the behavior of TLSA.