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Call admission control (CAC) functionality is a critical requirement for guarantee the desired quality of service (QoS) for voice calls in IP-based wireless networks. In this paper, three different CAC strategies for voice over IP (VoIP) traffic over wireless access networks with packet buffering are mathematically analyzed through a joint call and packet level discrete time teletraffic model. The admission criterion (i.e., admission threshold) of new sessions of these strategies is based on either the total number of sessions, the number of active sessions (i.e., sessions in talk-spurt periods), or the number of packets queued in the buffer. Admission threshold and buffer size can be both controlled for QoS provisioning in terms of session blocking and packet dropping probabilities. Arrivals and completions of VoIP sessions, on/off activity detection, and periodic and constant length packet generation (of active sessions) of individual VoIP sessions are modeled. The developed teletraffic analysis allows to evaluate the performance of the CAC strategies in terms of the most relevant QoS metrics of VoIP traffic at both call and packet level (i.e., session blocking and packet dropping probabilities and packet delay). Finally, the maximum traffic attained by the different studied-CAC strategies (while QoS provisioning is guaranteed) is obtained.Keywords-Call admission control; VoIP; joint call and packet level analysis; QoS provisioning; voice activity detection; session blocking; packet dropping probability; packet delay.

Due to the unpredictable nature of channel availability, supporting the quality of service (QoS) of stringent delay sensitive traffic in cognitive radio networks (CRNs) is very challenging. Stringent delay sensitive calls in CRNs are susceptible to forced termination due to the preemptive resource occupancy priority of primary users. To enable more efficient usage of the spectrum while improving the QoS experienced by secondary users (SUs), dynamic spectrum leasing (and coordinated cognitive radio) of resources has been previously proposed in the literature. In this paper, the Erlang capacity in coordinated cognitive radio networks with real-time hard delay constraint traffic as function of the rented resources is analytically calculated. For the adequate and fair performance comparison, call admission with fractional channel reservation to prioritize ongoing secondary calls over new ones is considered. From numerical results, it is observed that in CRNs exists a critical utilization factor of the primary resources from which it is not longer possible to guarantee the required QoS of SUs and, therefore, delay sensitive services cannot be even supported in cognitive radio networks. Thus, spectrum leasing can be essential for CRN operators to provide the QoS demanded by delay sensitive services. Then, the cost per capacity Erlang as function of both the utilization factor of the primary resources and the maximum allowed number of simultaneously rented channels is evaluated.Keywords-Coordinated cognitive radio networks; spectrum leasing; stringent delay sensitive traffic; QoS; Erlang capacity; call admission control; new call blocking and call forced termination.

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