In this paper, we present an analytical model of two-tier handoff mechanisms for a hierarchical NEMO system composed of access routers (ARs), mobile routers (MRs), and visiting mobile nodes (MNs). In the proposed two-tier handoff mechanism, service areas of MR and AR are respectively divided into handoff and non-handoff regions. Consequently, concurrent voice/data sessions in a hierarchical AR-MR model can be classified into four types according to the locations of MN and MR within the MR's and the AR's service areas, respectively. We build a mathematical model with 4-D Markov chains to analyze the performance in terms of the system utilization and the blocking probabilities of new sessions and handoff sessions. For the purpose of validation, we conduct experiments through simulation. Simulation results reveal that both the blocking probabilities of new sessions and handoff sessions are very close to the analytical results, particularly when the system utilization is high. The impacts of session residence time and session arrival rates on the blocking probabilities are also investigated.

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The quality of multimedia services over Internet could be seriously degraded due to unexpectedly increased end-to-end jitter. In this paper, we propose an innovative end-to-end jitter minimization mechanism with three-color marking (TCM). An earlyarrival packet is assignedfor a delayed-FIFO queue to consume extra credits. For a late-arrival packet, the highest-priority queue of weighted-round-robin (WRR) scheduling is allocated for exerting on reducing delay dejcit to avoid exceeding end-to-end delay constraints. We conduct experiments by simulation and the results reveal that the proposed scheme can achieve very satisfactory end-to-end delay jitter, especially for longer-length packets under heavy traflc load. The impact of using diflerent bufler sizes at a router to the packet loss rate and the end-to-end delay jitter is also investigated.

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