Link-layer fairness models that have been proposed for wireline and packet cellular networks cannot be generalized for shared channel wireless networks because of the unique characteristics of the wireless channel, such as location-dependent contention, inherent conflict between optimizing channel utilization and achieving fairness, and the absence of any centralized control. In this paper, we propose a general analytical framework that captures the unique characteristics of shared wireless channels and allows the modeling of a large class of systemwide fairness models via the specification of per-flow utility functions. We show that system-wide fairness can be achieved without explicit global coordination so long as each node executes a contention resolution algorithm that is designed to optimize its local utility function. We present a general mechanism for translating a given fairness model in our framework into a corresponding contention resolution algorithm. Using this translation...

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This paper studies TCP performance in a stationary multihop wireless network using IEEE 802.11 for channel access control. We first show that given a specific network topology and flow patterns, there exists an optimal window size W # at which TCP achieves the highest throughput via maximum spatial reuse of the shared wireless channel. However, TCP grows its window size much larger than W # , leading to throughput reduction. We then explain the TCP throughput decrease using our observations and analysis of the packet loss in an overloaded multihop wireless network. We find out that the network overload is typically first signified by packet drops due to wireless link-layer contention, rather than buffer overflow-induced losses observed in the wired Internet. As the offered load increases, the probability of packet drops due to link contention also increases, and eventually saturates. Unfortunately, the link-layer drop probability is insufficient to keep the TCP window size around W # . We model and analyze the link contention behavior, based on which we propose Link RED that fine-tunes the link-layer packet dropping probability to stabilize the TCP window size around W # . We further devise Adaptive Pacing to better coordinate channel access along the packet forwarding path. Our simulations demonstrate 5% to 30% improvement of TCP throughput using the proposed two techniques.

This paper investigates differentiated services in wireless packet networks using a fully distributed approach that supports service differentiation, radio monitoring, and admission control. While our proposal is generally applicable to distributed wireless access schemes, we design, implement, and evaluate our framework within the context of existing wireless technology. Service differentiation is based on the IEEE 802.11 Distributed Coordination Function (DCF) originally designed to support best-effort data services. We analyze the delay experienced by a mobile host implementing the IEEE 802.11 DCF and derive a closed-form formula.We then extend the DCF to provide service differentiation for delay-sensitive and best-effort traffic based on the results from the analysis. Two distributed estimation algorithms are proposed. These algorithms are evaluated using simulation, analysis, and experimentation. A Virtual MAC (VMAC) algorithm passively monitors the radio channel and estimates locally achievable service levels. The VMAC estimates key MAC level statistics related to service quality such as delay, delay variation, packet collision, and packet loss. We show the efficiency of the VMAC algorithm through simulation and consider significantly overlapping cells and highly bursty traffic mixes. In addition, we implement and evaluate the VMAC in an experimental differentiated services wireless testbed. A Virtual Source (VS) algorithm utilizes the VMAC to estimate application -level service quality. The VS allows application parameters to be tuned in response to dynamic channel conditions based on "virtual delay curves." We demonstrate through simulation that when these distributed virtual algorithms are applied to the admission control of the radio channel then a globally st...

We study the interaction between communication protocols, network topology and packet traffic in wireless static radio networks. A particular interest is to empirically characterize the effect of interaction between the routing layer and the MAC layer on overall system performance. Three well known MAC protocols: 802.11, CSMA, and MACA are considered. Similarly three recently proposed routing protocols: AODV, DSR and LAR scheme 1 are considered. The performance of the protocols is measured with regard to three important parameters: (i) number of packets received (ii) average latency of each packet and (iii) long term fairness.

This paper studies TCP performance over static, ad hoc networks that use IEEE 802.11 protocol as the access method. Our study reveals some interesting results. First, there exists an optimal value for TCP congestion window size, at which the TCP throughput is maximized. However, TCP does not operate around this optimal point, and typically grows its window much larger; this leads to decreased throughput and increased packet loss. To better understand this behavior, we further study the characteristics of TCP packet loss. Our results show that, network overload is mainly signified by wireless link contention. As long as the buffer size at each node is reasonable (larger than 10 packets), buffer overflow-induced packet loss is rare and packet drops due to link-layer contention dominate. Link-layer drops offer the first sign for network overload. We further observe that multihop wireless links collectively demonstrate Random Early Detection (RED) like graceful drop behavior, but the current TCP protocol does not adapt well to this built-in grace drop characteristic. We further propose two techniques of link RED and adaptive spacing at the link layer, and simulations show that they can improve TCP throughput by 5% to 30%.

1997. Unfortunately, the medium access protocol described in the standard meets some problems that arise from the presence of so-called hidden stations. This situation can cause degradation of the network performance. The paper describes a simulation analysis of influence of hidden stations on the IEEE 802.11 network efficiency in four different hidden terminals scenarios. The throughput and the mean packet delay as a function of the offered load has been studied. The presented results allow us to determine the usefulness of RTS/CTS mechanism usage in the presence of hidden stations. 1.

This paper investigates differentiated services in wireless packet networks using a fully distributed approach that supports service differentiation, radio monitoring and admission control. Service differentiation is based on the IEEE 802.11 Distributed Coordination Function (DCF) originally designed to support best-effort data services. We extend the Distributed Coordination Function to provide service differentiation for delay sensitive and best-effort traffic. Two distributed estimation algorithms are proposed and analyzed. A Virtual MAC (VMAC) algorithm passively monitors the radio channel and estimates locally achievable service levels. The Virtual MAC estimates key MAC level statistics related to service quality such as delay, delay variation, packet collision and packet loss. We show the efficiency of the Virtual MAC algorithm and consider significantly overlapping cells and highly bursty traffic mixes. A Virtual Source (VS) algorithm utilizes the Virtual MAC to estimate application level service quality. The Virtual Source allows application parameters to be tuned in response to dynamic channel conditions based on "virtual delay curves". We demonstrate through simulation that when these distributed virtual algorithms are applied to the admission control of the radio channel then a globally stable state can be maintained without the need for complex centralized radio resource management. Finally, we discuss a distributed service level management scheme that builds on the proposed algorithms to offer continuous service with handoff. I.

This paper investigates differentiated services in wireless packet networks using a fully distributed approach that supports service differentiation, radio monitoring and admission control. Service differentiation is based on the IEEE 802.11 Distributed Coordination Function (DCF) originally designed to support best-effort data services. We extend the Distributed Coordination Function to provide service differentiation for delay sensitive and best-effort traffic. Two distributed estimation algorithms are proposed and analyzed. A Virtual MAC (VMAC) algorithm passively monitors the radio channel and estimates locally achievable service levels. The Virtual MAC estimates key MAC level statistics related to service quality such as delay, delay variation, packet collision and packet loss.

Karpagam college of engineering,