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The unavailability of end-to-end traffic in mesh networks with failure-independent path-protecting (FIPP) p-cycles is examined, and an availability-aware network design method is presented for the same. The efficiency of FIPP p-cycles is compared with that of span-protecting p-cycles when the network design limits unavailability, and results reveal that the FIPP p-cycles are less efficient with 8-13% higher redundancy than span-protecting p-cycles when the service unavailability is limited.

We address two issues of contemporary interest in the area of enhancing the performance of ad hoc networks, where the IEEE 802.11 distributed coordination function (DCF) is the adopted medium-access control (MAC). We investigate the effects that transmission power control and tuning carrier sensing (CS) threshold have on network throughput, and we study the interplay between them. To accomplish this, we develop a realistic analytical model that characterizes the transmission activities that are governed by the IEEE 802.11 DCF in a single-channel power-aware multihop wireless network. We observe that selecting a smaller CS threshold will severely impact the spatial reuse, whereas a larger CS threshold will yield excessive interference among concurrent transmissions. Accordingly, we discovered that performing power control has either a minor or negligible effect in both situations, respectively. Furthermore, when the CS threshold is selected appropriately, power control shows its effectiveness in reducing collisions and, hence, improving system performance. Finally, using our model, we demonstrate the potential adverse impacts of request-to-send/clear-to-send (RTS/CTS) control packets on the network capacity and compare its performance with the two-way basic access method. Index Terms--IEEE 802.11, modeling, physical carrier sensing (PCS), power control, throughput.

Wireless access protocols currently deployed in mobile ad hoc networks use distributed contention resolution mechanisms for sharing the wireless channel. In such an environment, selfish hosts that fail to adhere to the medium access control (MAC) protocol may obtain an unfair share of the channel bandwidth at the expense of performance degradation of well-behaved hosts. We present a novel access method, called predictable random backoff (PRB), that is capable of mitigating the misbehavior of selfish hosts, particularly hosts that deliberately do not respect the random deferment of the transmission of their packets. PRB is based on minor modifications of the IEEE 802.11 binary exponential backoff (BEB) and forces each node to generate a predictable backoff interval. The key idea is to adjust, in a predictable manner, the lower bound of the contention window to enhance the per-station fairness in selfish environments. Hosts that do not follow the operation of PRB are therefore easily detected and isolated. We present an accurate analytical model to compute the system throughput using a 3-D Markov chain. We evaluate the performance of PRB under the normal case and in the presence of selfish hosts. Our results show that PRB and BEB similarly perform in the former case. Selfish hosts, however, achieve substantially higher throughput than well-behaved hosts under BEB. PRB, on the other hand, can effectively enhance IEEE 802.11 BEB by mitigating the impacts of these MAC selfish misbehaviors and guarantee a fair share of the wireless channel for well-behaved hosts. Index Terms--Ad hoc networks, IEEE 802.11, medium access control (MAC), performance evaluation, selfish misbehavior.

Medium access control (MAC) protocols simulta. neously integrating transmission power (TP) control with directional antennas have the potential to enhance both energy savings and capacity throughput in wireless multihop Mobile Ad hoc NETworks (MANETs). In this paper, we present a model to calculate future interference in networks with directional antennas, and based on this model, we derive some relations that should exist between the required TP of RTS, CTS, DATA, and ACK frames for successful data packet delivery in MANETs based on the directional version of the IEEE 802.11 distributed coordination function. From these relations, we propose a distributed power control scheme. Furthermore, we show, via simulations, that the true potentials from the proposed control scheme cannot be shown due to the imperfection of the derived model. Based on these observations, we introduce another class of power control algorithm that instead deploys a prediction filter (Kalman or extended Kalman) to estimate future interference. Simulation experiments for different topologies are used to verify the significant throughput and energy gains that can be obtained by the proposed power control schemes. Index Terms--Directional antenna, interference, Kalman filter, Mobile Ad hoc NETwork (MANET), power control.

The emerging IEEE 802.11e standard is expected to provide service differentiation and resource allocation for realtime traffic. To support the transmission of voice and multimedia data with performance guarantees, it is crucial to design efficient algorithms for admission control and resource allocation (particularly under heavy load), and several methods have been proposed to date. However, most of these proposed methods may not be efficient, because they assign channel access parameters (CAPs) according to the access category into which a flow is mapped rather than the absolute quality-of-service (QoS) requirements of the flow. Using simulations, we highlight the shortcomings of current admission control methods, and accordingly, we propose a flow-based service differentiation mechanism. We introduce the proper 'per-flow' selection of CAPs based on the QoS requirements of traffic flows. Furthermore, the new flow-based admission can control and adjust CAPs with the channel condition variations. We validate our reasoning through extensive simulations and a thorough comparison with other schemes. Index Terms--Admission control, IEEE 802.11e, wireless networks.