Blocking Probability with Time-driven Priority Scheduling

This paper provides a methodology for evaluating call blocking probability over packet-switched networks with Time-driven priority (TDP) [4][5] and obtained results. The approach presented in this work is novel, since call blocking is typically studied in the context of circuit-switched networks. TDP together with resource reservation enable real-time delivery of packets with no loss due to congestion and constant jitter of one time frame (TF)–typically between 12.5 μs and 125 μs. Resource reservation for a call (or multiple calls) over a TDP network requires to find a schedule. A call may not be accepted for two reasons (i) there is no capacity–the call is rejected–or (ii) there is capacity but no schedule–the call is blocked. This work studies the call blocking probability as a function of the link utilization, since call blocking can possibly lead to low link utilization. In other words, it may not be possible to fully utilize the network because of unschedulability (i.e., the inability to find a schedule). The results show that it is possible to achieve high link utilization and that call blocking, in most cases, is negligible. Moreover, the result shows how the blocking problem diminishes as the link bandwidth increases. This is achieved without increasing the complexity of the schedule computation and the scheduler run-time operation in TDP switches.