Access Point (AP) selection in WiFi hotspots is driven by stations and it is based on the measured strongest RSSI (Received Signal Strength Indicator) level: any station connects to the AP that provides the higher physical data rate. Although simple and effective in low crowded scenarios with low-medium traffic load, this strategy performs inefficiently when the number of mobile users is high and their distribution among APs is unbalanced, i.e. when network congestion becomes an issue. Load Balancing (LB) solutions aim at solving this problem by enforcing the connection of stations to the AP having either the smallest number of associated stations or the lowest traffic load. However, LB solutions do not account for traffic priorities or, when they consider them, they do not deal with the joint configuration of QoS (Quality of Service) and LB parameters. In this study we present a framework for modeling, analyzing and designing QoS-aware LB solutions. The proposed framework assumes that stations implement the Enhanced Distributed Channel Access (EDCA) mechanism of the IEEE 802.11e standard. Moreover, in order to make the framework concrete, we assume that the QoS goal is the weighted fair allocation of wireless resources. However, the framework is not restricted to this goal and can be easily extended in order to deal with a different cost function. The proposed framework is validated through simulations in a typical indoor LB scenario. The results show that the model is effective in capturing network performance and in designing LB solutions that account for traffic priorities and the configuration of QoS parameters.

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This paper presents a comparative study between JET (Just Enough Time) and a number of new preemptive channel scheduling algorithms in Optical Burst Switching (OBS) with QoS (Quality of Service) requirement. In terms of performance criteria, loss rate in byte, access delay and end-toend delay are considered. A 2-state MMPP (Markov Modulated Poisson Process) traffic generator on a 14-node mesh network topology illustrating NSFNET is designed as the testbed. NS2 Network Simulation tool is used for our tests. Bursts are created using a hybrid model that takes into account both timeout and maximum length threshold mechanisms. In core and edge nodes, in order to satisfy QoS requirements two mechanisms such as Regulative Wavelength Grouping (RWG) and priority based queuing are used. RWG mechanism, where the number of wavelengths for each traffic class is arranged for adjusting the burst drop probability of traffic classes under a specific threshold value, is used for providing priority levels in core nodes. In priority based queuing, bursts are sent according to their priority order, in edge nodes. Simulation works have shown that our preemptive channel scheduling algorithms give better results compared to the other studied algorithms while considering QoS.

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