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Attacking and Securing Beacon-Enabled 802.15.4 NetworksJUNG, SANG SHIN 04 May 2011 (has links)
The IEEE 802.15.4 has attracted time-critical applications in wireless sensor networks (WSNs) because of its beacon-enabled mode and guaranteed timeslots (GTSs). However, the GTS scheme’s security still leave the 802.15.4 MAC vulnerable to attacks. Further, the existing techniques in the literature for securing 802.15.4 either focus on non beacon-enabled 802.15.4 or cannot defend against insider attacks for beacon-enabled 802.15.4. In this thesis, we illustrate this by demonstrating attacks on the availability and integrity of the beacon-enabled 802.15.4. To proof the attacks, we implement the attacks using Tmote Sky motes for a malicious node along with regular nodes. We show that the malicious node can freely exploit the beacon frames to compromise the integrity and availability of the network. For the defense, we present beacon-enabled MiniSec (BCN-MiniSec) and analyze its cost.
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The Efficacy of Source Rate Control in Achieving Fairness in Wireless Mesh NetworksLi, Lily Lei January 2007 (has links)
The use of 802.11-based wireless mesh networks (WMNs) as an alternative network backbone technology is growing rapidly. The primary advantages of this approach are
ease of deployment and lower cost. However, such networks typically exhibit poor fairness
properties, often starving nodes if they are too many hops distant from the gateway.
Researchers have shown a growing interest in this problem in recent years. Many solutions
proposed amount to some level of source rate control, either by policing directly
at the source, or via TCP congestion control reacting to a gateway-enforced rate limit.
However, there has been limited study on the effectiveness of source rate control.
In this thesis we first demonstrate that source rate control can only partially solve the fairness issue in 802.11-based WMNs, with some routers experiencing an undesirable
degree of unfairness, which we call structural unfairness. We then identify the four necessary factors that cause structural unfairness. If we can eliminate or reduce any one of these conditions, we can eliminate or ameliorate the unfairness problem. We first investigate two techniques to improve 802.11 MAC scheduling: fixing the contention window
and packet spacing at every router node, both means achievable with commodity 802.11
hardware. We show that the combination of these mechanisms provides a significant
gain in fairness. We also perform case studies using another three techniques, channel re-assignment, routing changes, and careful router placement, to remove or reduce other necessary conditions. We demonstrate that these techniques, whenever applicable, can eliminate the unfairness problem entirely at times, or at least improve the situation.
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An Efficient QoS MAC for IEEE 802.11p Over Cognitive Multichannel Vehicular NetworksEl Ajaltouni, Hikmat 22 February 2012 (has links)
One of the most challenging issues facing vehicular networks lies in the design of an
efficient MAC protocol due to mobile nature of nodes, delay constraints for safety applications and interference. In this thesis, I propose an efficient Multichannel QoS Cognitive MAC (MQOG). MQOG assesses the quality of channel prior to transmission employing dynamic channel allocation and negotiation algorithms to achieve significant increase in channel reliability,
throughput and delay constraints while simultaneously addressing Quality of Service.
The uniqueness of MQOG lies in making use of the free unlicensed bands. To consider
fair effective sharing of resources I propose a Mobility Based Dynamic Transmit Opportunity
(MoByToP) while modifying the 802.11e TXOP (Transmit Opportunity). The proposed protocols were implemented in OMNET++ 4.1, and extensive experiments demonstrated a faster and more efficient reception of safety messages compared to existing VANet MAC Protocols. Finally, improvements in delay, packet delivery ratios and throughput were noticed.
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Energy-Efficient Battery-Aware MAC protocol for Wireless Sensor NetworksNasrallah, Yamen 19 March 2012 (has links)
Wireless sensor networks suffer from limited power resources. Therefore, managing the energy
constraints and exploring new ways to minimize the power consumption during the operation of
the nodes are critical issues. Conventional MAC protocols deal with this problem without
considering the internal properties of the sensor nodes’ batteries. However, recent studies about
battery modeling and behaviour showed that the pulsed discharge mechanism and the charge
recovery effect may have a significant impact on wireless communication in terms of power
saving. In this thesis we propose two battery-aware MAC protocols that take benefit of these
factors to save more energy and to prolong the lifetime of the nodes/network without affecting
the throughput. In both protocols we measure the remaining battery capacity of the node and use
that measurement in the back-off scheme. The first protocol gives the nodes with higher
remaining battery capacity more priority to access the medium, while the other one provides
more medium access priority to the nodes with lower remaining battery capacity. The objective
is to investigate, through simulations, which protocol reduces the power consumption of the
nodes, improve the lifetime of the network, and compare the results with the CSMA-CA
protocol.
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The Efficacy of Source Rate Control in Achieving Fairness in Wireless Mesh NetworksLi, Lily Lei January 2007 (has links)
The use of 802.11-based wireless mesh networks (WMNs) as an alternative network backbone technology is growing rapidly. The primary advantages of this approach are
ease of deployment and lower cost. However, such networks typically exhibit poor fairness
properties, often starving nodes if they are too many hops distant from the gateway.
Researchers have shown a growing interest in this problem in recent years. Many solutions
proposed amount to some level of source rate control, either by policing directly
at the source, or via TCP congestion control reacting to a gateway-enforced rate limit.
However, there has been limited study on the effectiveness of source rate control.
In this thesis we first demonstrate that source rate control can only partially solve the fairness issue in 802.11-based WMNs, with some routers experiencing an undesirable
degree of unfairness, which we call structural unfairness. We then identify the four necessary factors that cause structural unfairness. If we can eliminate or reduce any one of these conditions, we can eliminate or ameliorate the unfairness problem. We first investigate two techniques to improve 802.11 MAC scheduling: fixing the contention window
and packet spacing at every router node, both means achievable with commodity 802.11
hardware. We show that the combination of these mechanisms provides a significant
gain in fairness. We also perform case studies using another three techniques, channel re-assignment, routing changes, and careful router placement, to remove or reduce other necessary conditions. We demonstrate that these techniques, whenever applicable, can eliminate the unfairness problem entirely at times, or at least improve the situation.
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The Mobility Impact in IEEE 802.11p Infrastructureless Vehicular NetworksAlasmary, Waleed 15 April 2010 (has links)
Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. Due to high speed of nodes and their frequent disconnections, it is difficult to design a MAC scheme in VANETs that satisfies the quality-of-service requirements in all networking scenarios. In this thesis, we provide a comprehensive evaluation of the mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay, as well as the impact of mobility factors. The study also presents a relation between the mobility factors and the respective medium access behavior. Moreover, a new unfairness problem according to node relative speed is identified for both broadcast and unicast scenarios. To achieve better performance, we propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. Extensive simulation results show the significant impact of mobility on the IEEE 802.11p MAC performance, an identification of a new unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.
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Efficient GTS Allocation Schemes for IEEE 802.15.4Haque, Syed E 11 April 2012 (has links)
IEEE 802.15.4 is a standard defined for wireless sensor network applications with limited power and relaxed throughput needs. The devices transmit data during two periods: Contention Access Period (CAP) by accessing the channel using CSMA/CA and Contention Free Period (CFP), which consists of Guaranteed Time Slots (GTS) allocated to individual devices by the network coordinator. The GTS is used by devices for cyclic data transmission and the coordinator can allocate GTS to a maximum of only seven devices. In this work, we have proposed two algorithms for an efficient GTS allocation. The first algorithm is focused on improving the bandwidth utilization of devices, while the second algorithm uses traffic arrival information of devices to allow sharing of GTS slots between more than seven devices. The proposed schemes were tested through simulations and the results show that the new GTS allocation schemes perform better than the original IEEE 802.15.4 standard.
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Implementation of the IEEE 802.11a MAC layer in C language / Implementering av IEEE 802.11a MAC-lagret i programspråket CGuillen, Carlos Alonso January 2004 (has links)
Wireless communication is being developed in the last years day by day, there are several standards that talks about it. We are going to go through the IEEE standard 802.11 which talks about wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Looking this more carefully we will study MAC specifications and its environment. The work that ISY department at Institute of Technology of Linkoping University has proposed is to design a MAC sublayer implementation for WLANs using C language programming and testing it with the test environment called “test bench”. This test bench will simulate LLC sublayer and PHY layer, in this way, our MAC implementation will has to interact with it. Therefore we will simulate a wireless network where we are going to have a short number of stations and we are going to look at carefully the MAC sublayer response in an ad hoc network.
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Investigation of IEEE standard 802.16 Medium AccessRobles Rico, Pedro Francisco January 2006 (has links)
This paper is a study of IEEE Standard 802.16 Medium Access Control (MAC) Layer in Distributed Mesh Networks. IEEE Standard 802.16 is a Wireless Metropolitan Area Network (WMAN) technology that can connect different IEEE 802.11 (Wifi) host post with each other and to other parts of internet. It can provide network for a wireless router and at the same time this router can be installed in the office, house or university. WiMAX (Worldwide Interoperability for Microwave Access) is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. Products that pass the conformity tests for WiMAX are capable of forming wireless connections between them to permit the carrying of internet packet data. The idea of WiMAX is similar than Wi-Fi but it is not the same. It is a step much higher than Wi-Fi because it is focused to offer internet for a whole city. It has much higher capacity and longer distances. IEEE 802.16 defines a MAC Layer that supports multiple physical layer (PHY) Specifications and different topologies; Point to Multipoint (PMP) and Mesh Networks. In this first topology there exist a Base Station (BS) that have direct links with all the Subscriber Stations (SS). If any Subscriber Station requires transmitting to another SS, the message must convey the Base Station.
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Performance Analysis of Distributed MAC Protocols for Wireless NetworksLing, Xinhua 01 May 2007 (has links)
How to improve the radio resource utilization and provide better
quality-of-service (QoS) is an everlasting challenge to the
designers of wireless networks. As an indispensable element of
the solution to the above task, medium access control (MAC)
protocols coordinate the stations and resolve the channel access
contentions so that the scarce radio resources are shared fairly
and efficiently among the participating users. With a given
physical layer, a properly designed MAC protocol is the key to
desired system performance, and directly affects the perceived QoS
of end users.
Distributed random access protocols are widely used MAC protocols
in both infrastructure-based and infrastructureless wireless
networks. To understand the characteristics of these protocols,
there have been enormous efforts on their performance study by
means of analytical modeling in the literature. However, the
existing approaches are inflexible to adapt to different protocol
variants and traffic situations, due to either many unrealistic
assumptions or high complexity.
In this thesis, we propose a simple and scalable generic
performance analysis framework for a family of carrier sense
multiple access with collision avoidance (CSMA/CA) based
distributed MAC protocols, regardless of the detailed backoff and
channel access policies, with more realistic and fewer
assumptions. It provides a systematic approach to the performance
study and comparison of diverse MAC protocols in various
situations. Developed from the viewpoint of a tagged station, the
proposed framework focuses on modeling the backoff and channel
access behavior of an individual station. A set of fixed point
equations is obtained based on a novel three-level renewal process
concept, which leads to the fundamental MAC performance metric,
average frame service time. With this result, the important
network saturation throughput is then obtained straightforwardly.
The above distinctive approach makes the proposed analytical
framework unified for both saturated and unsaturated stations.
The proposed framework is successfully applied to study and
compare the performance of three representative distributed MAC
protocols: the legacy p-persistent CSMA/CA protocol, the IEEE
802.15.4 contention access period MAC protocol, and the IEEE
802.11 distributed coordination function, in a network with
homogeneous service. It is also extended naturally to study the
effects of three prevalent mechanisms for prioritized channel
access in a network with service differentiation. In particular,
the novel concepts of ``virtual backoff event'' and ``pre-backoff
waiting periods'' greatly simplify the analysis of the arbitration
interframe space mechanism, which is the most challenging one
among the three, as shown in the previous works reported in the
literature. The comparison with comprehensive simulations shows
that the proposed analytical framework provides accurate
performance predictions in a broad range of stations. The results
obtained provide many helpful insights into how to improve the
performance of current protocols and design better new ones.
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