Andrzej R. Pach

A simple but accurate throughput model for IEEE 802.11 EDCA in saturation and non-saturation conditions

This paper presents a novel mathematical model of the IEEE 802.11 Enhanced Distributed Channel Access (EDCA) function. The main advantage of the model is that it combines accurate probability of counting down backoff slots with proper handling of frames. Furthermore, it allows for traffic differentiation with the use of traffic priority-dependent access parameters, i.e., AIFSN, and CW. Additionally, a new method of modelling AIFS differentiation between traffic classes is proposed. Finally, the model is kept reasonably simple and constructed in such a way that taking into account the four-way-handshake mechanism is uncomplicated. The proposed model is compared with simulations as well as numerical results obtained for two other models presented in the literature. The comparison gives satisfactory results regardless of the offered load, number of nodes, or network configuration.

An analysis of the backoff mechanism used in IEEE 802.11 networks

This paper presents a simulation analysis of the backoff mechanism presented in the IEEE 802.11 standard. The obtained simulations allow us to determine the effective throughput and the mean packet delay versus offered load for different values of the contention window parameter and the number of contending stations. The choice of the CWmin and CWmax parameters was analyzed. In particular, the choice of CWmin value in dependence of the number of transmitting stations was presented. The simulation results show that the proper choice of the CW parameters has a substantial influence on the network performance.

Management of security in quantum cryptography

The interest in quantum-based security methods has been growing rapidly in recent years. New implementations of quantum key distribution and new network services supported by this solution are being introduced. The reason behind the growing popularity of quantum cryptography is its unrivaled security level: all eavesdroppers can be revealed through the application of the laws of physics. First of all, the rules of quantum mechanics ensure that any measurement modifies the state of the transmitted quantum bit. This modification can be discovered by the sender and the receiver. This makes passive eavesdropping impossible. Using protocols such as BB84, network users are able to send a string of bits coded by the polarized photons. After that, they can establish secure cryptographic keys through an unsecure channel using different key distillation methods. Major ongoing challenges include the control and management of security in systems using quantum cryptography, as well as tailoring security to specific end users requirements and services.

An IEEE 802.11 EDCA model with support for analysing networks with misbehaving nodes

We present a novel model of IEEE 802.11 EDCA with support for analysing networks with misbehaving nodes. In particular, we consider backoff misbehaviour. Firstly, we verify the model by extensive simulation analysis and by comparing it to three other IEEE 802.11 models. The results show that our model behaves satisfactorily and outperforms other widely acknowledged models. Secondly, a comparison with simulation results in several scenarios with misbehaving nodes proves that our model performs correctly for these scenarios. The proposed model can, therefore, be considered as an original contribution to the area of EDCA models and backoff misbehaviour.

Impact of Contention Window Cheating on Single-Hop IEEE 802.11e MANETs

This paper presents a work in progress which deals with the important and unresolved problem of node misbehavior. A realistic approach is used to determine the impact of contention window manipulation on IEEE 802.11e ad-hoc networks. It is explained why such networks are more prone to misbehavior. Novel results pertaining to the 802.11e standard are presented. Simulation analysis is done for several scenarios with a distinction made for uplink and downlink traffic. It is shown that a misbehaving node can jeopardize network performance, therefore, countermeasures to this problem need to be developed.

BusySiMOn - A New Protocol for IEEE 802.11 EDCA-Based Ad-Hoc Networks with Hidden Nodes

This article presents a new MAC layer protocol for IEEE 802.11 EDCA-based ad-hoc networks with hidden nodes. The key idea of the proposed solution is based on an intelligent two-step reservation procedure which is combined with the advantages of EDCA service differentiation. The new protocol achieves significant performance improvement for high priority traffic (e.g., Voice) in terms of fairness, throughput and average frame delay. It is also compatible with the IEEE 802.11 standard. The obtained results emphasize the advantages of the new protocol over the currently used four-way handshake mechanism.

A Performance Analysis of IEEE 802.11 Networks in the Presence of Hidden Stations

IEEE 802.11 is a wireless network standard that was completed in 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.

Improving QoS and security in wireless ad hoc networks by mitigating the impact of selfish behaviors: a game‐theoretic approach

Selfish users are known to be a severe security threat for wireless ad hoc networks. In particular, they can exploit mechanisms designed to assure quality of service (QoS) in the network. In this paper, the problem of backoff misbehavior in IEEE 802.11 enhanced distributed channel access (EDCA) networks is studied using a game-theoretic approach. First, it is shown how this selfish behavior can disrupt traffic differentiation. Then, a solution is proposed, which encourages standard-compliant behavior and thus proper QoS provisioning. This solution is based on punishing selfish nodes by degrading their throughput proportionally to the degree of misbehavior. A practical application of the solution is proposed, which is verified through simulations. Results show that the suggested mechanism considerably improves QoS provisioning in IEEE 802.11 EDCA ad hoc networks in the presence of selfish nodes. Furthermore, it is shown that the mechanism is adaptive, does not have a negative impact on the throughput of well-behaving nodes, and provides legacy node support. Copyright

An analysis of the influence of the threshold parameter on the IEEE 802.11 network performance

This paper presents a simulation analysis of the influence of the RTS-threshold parameter on the IEEE 802.11 network performance. The throughput and the mean frame delay as functions of the offered load for different RTS-threshold values and number of stations transmitting frames of a random size are studied. The optimal value of the RTS-threshold as a function of the number of contending stations is determined. This allows us to design an IEEE 802.11 network in such a way that can substantially improve its performance.

Analysis of IEEE 802.11e Line Topology Scenarios in the Presence of Hidden Nodes

In this paper an innovative simulation study of five IEEE 802.11e network configurations is presented. The conducted analysis is crucial for understanding how a theoretically simple and, most of all, popular line topology network can be degraded by the presence of hidden and exposed nodes. The discussion of the obtained results helps to understand how and why the behavior of IEEE 802.11e based line topologies changes when the number of nodes increases. Furthermore, the usefulness of the four-way handshake mechanism is argued. Finally, the need for a better MAC protocol is stressed and a number of novel conclusions about the IEEE 802.11e nature is provided.