270 research outputs found
On Efficiency and Validity of Previous Homeplug MAC Performance Analysis
The Medium Access Control protocol of Power Line Communication networks
(defined in Homeplug and IEEE 1901 standards) has received relatively modest
attention from the research community. As a consequence, there is only one
analytic model that complies with the standardised MAC procedures and considers
unsaturated conditions. We identify two important limitations of the existing
analytic model: high computational expense and predicted results just prior to
the predicted saturation point do not correspond to long-term network
performance. In this work, we present a simplification of the previously
defined analytic model of Homeplug MAC able to substantially reduce its
complexity and demonstrate that the previous performance results just before
predicted saturation correspond to a transitory phase. We determine that the
causes of previous misprediction are common analytical assumptions and the
potential occurrence of a transitory phase, that we show to be of extremely
long duration under certain circumstances. We also provide techniques, both
analytical and experimental, to correctly predict long-term behaviour and
analyse the effect of specific Homeplug/IEEE 1901 features on the magnitude of
misprediction errors
MAC design for WiFi infrastructure networks: a game-theoretic approach
In WiFi networks, mobile nodes compete for accessing a shared channel by
means of a random access protocol called Distributed Coordination Function
(DCF). Although this protocol is in principle fair, since all the stations have
the same probability to transmit on the channel, it has been shown that unfair
behaviors may emerge in actual networking scenarios because of non-standard
configurations of the nodes. Due to the proliferation of open source drivers
and programmable cards, enabling an easy customization of the channel access
policies, we propose a game-theoretic analysis of random access schemes.
Assuming that each node is rational and implements a best response strategy, we
show that efficient equilibria conditions can be reached when stations are
interested in both uploading and downloading traffic. More interesting, these
equilibria are reached when all the stations play the same strategy, thus
guaranteeing a fair resource sharing. When stations are interested in upload
traffic only, we also propose a mechanism design, based on an artificial
dropping of layer-2 acknowledgments, to force desired equilibria. Finally, we
propose and evaluate some simple DCF extensions for practically implementing
our theoretical findings.Comment: under review on IEEE Transaction on wireless communication
Adaptive EDCF: Enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks
This paper describes an adaptive service differentiation scheme for QoS enhancement in IEEE 802.11 wireless ad-hoc networks. Our approach, called adaptive enhanced distributed coordination function (AEDCF), is derived from the new EDCF introduced in the upcoming IEEE 802.11e standard. Our scheme aims to share the transmission channel efficiently. Relative priorities are provisioned by adjusting the size of the contention window (CW) of each traffic class taking into account both applications requirements and network conditions. We evaluate through simulations the performance of AEDCF and compare it with the EDCF scheme proposed in the 802.11e. Results show that AEDCF outperforms the basic EDCF, especially at high traffic load conditions. Indeed, our scheme increases the medium utilization ratio and reduces for more than 50% the collision rate. While achieving delay differentiation, the overall goodput obtained is up to 25% higher than EDCF. Moreover, the complexity of AEDCF remains similar to the EDCF scheme, enabling the design of cheap implementations
Class-Based Weighted Window for TCP Fairness in WLANs
The explosive growth of the Internet has extended to the wireless domain. The number of Internet users and mobile devices with wireless Internet access is continuously increasing. However, the network resource is essentially limited, and fair service is a key issue in bandwidth allocation. In this research, the focus is on the issue of fairness among wireless stations having different number and direction of flows for different required bandwidth to ensure that fair channel is fairly shared between wireless stations in the same class of bandwidth. It is shown that the current WLANs allocate bandwidth unfairly. It is also identified that the cause of this problem of unfairness is the TCP cumulative ACK mechanism combined with the packet dropping mechanism of AP queue and the irregular space for each wireless station in AP queue. The proposed method allocate converged bandwidth by introducing a Class-Based Weighted Window method which adjusts the TCP window size based on the current conditions of the network and according to the networkâs requirements. This method works in wireless stations without requiring any modification in MAC. It can guarantee fair service in terms of throughput among wireless users whether they require the same or different bandwidth.Wireless LAN, TCP, Fairness
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