Mobile Ad Hoc Networks (MANETs)

Mobile Ad Hoc Networks (MANETs) Introduction What is Mobile Ad Hoc Network? With rapid development of wireless technology, the Mobile Ad Hoc Network (MANET) has emerged as a new type of wireless network. MANET is a collection of wireless mobile nodes (e.g. laptops) that dynamically function as a network without the use of any existing infrastructure and centralized administration. It is an autonomous system where each node operates not only as an end system but also as a router to forward packets for other nodes. Since the nodes in MANET move around, the wireless links break and re-establish frequently. Furthermore, most of mobile nodes are resource limited in computing capability and battery power and therefore traditional computing content routing protocols are not suitable for MANET. Several ad hoc routing protocols have been proposed for each node acting as router and maintaining routing information. There are many other applications of MANET. For examples, MANET can be used to provide emergency Services when the network is impaired due to the damaging of existing infrastructure [8]. Computer scientists have predicted a world of ubiquitous computing in which computers will be all around us, constantly performing mundane tasks to make our lives a little easier. These ubiquitous computers connect in mobile ad hoc mode and change the environment or react to the change of the environment where they are suited. MANET is also found useful in the so-called sensor dust network to coordinate the activities and reports of a large collection of tiny sensor devices which could offer detailed information about terrain or environmental dangerous conditions. Problem Statement and Motivation Most current ad hoc routing protocols assume that the wireless network is benign and every node in the network strictly follows the routing behavior and is willing to forward packets for other nodes. Most of these protocols cope well with the dynamically changing topology. However, they do not address the problems when misbehavior nodes present in the network.A commonly observed misbehavior is packet dropping. In a practical MANET, most devices have very limited computing and battery power while packet forwarding consumes a lot of such resources. Thus some of the mobile devices would not like to forward the packets for the benefit of others and they drop packets not destined to them. On the other hand, they still make use of other nodes to forward packets that they originate. These misbehaved nodes are very difficult to identify because we cannot tell that whether the packets are dropped intentionally by the misbehaved nodes or dropped due to the node having moved out of transmission range or other link error. Packet drop significantly decreases the network performance.Traditional security mechanisms are generally not suitable for MANET because: The network lacks central infrastructure to apply traditional security mechanism such as access control, authentication and trusted third party. Limited bandwidth, battery lifetime, and computation power prohibits the deployment of complex routing protocols or encryption algorithms. New security models or mechanisms suitable for MANET must be found. Network topologies and memberships are constantly changing. Thus new intrusion detection system and entity recognition mechanisms that are suitable for mobile ad hoc networks must be designed to avoid or mitigate the behavior to the networks. Trust management systems have been recently introduced as a security mechanism in MANET. In a trust management system, a communicating entity collects evidence regarding competence, honesty or security of other network participants with the purpose of making assessment or decisions regarding their trust relationships. Here trust Objective and Sub-tasks means the confidence of an entity on another entity based on the expectation that the other entity will perform a particular action important to the trustor, irrespective of the ability to monitor or control that other entity . For example, a trust-based routing protocol can collect the evidence of nodes misbehaving, form trust values of the nodes and select safest routes based on the trust metrics.Reputations systems are often seen as a derivation of trust management system. In the reputation system, an entity forms its trust on another entity based not only on the selfobserved evidence but also on the second hand information from third parties. One of the influential reputation systems is the DSR protocol. In the trust management system, reputation system and other trust-based systems, route selection is based on the sending nodes prior experience with other nodes in the network. Its opinions about how other entities are honest are constantly changing. Thus, we call the trust manag ement systems and their derivations as dynamic feedback mechanisms. The dynamic feedback mechanisms are usually applied on the current ad hoc routing protocols to rate the trust about other nodes in the network and make routing decisions based on the trust matrix, which is formed according to the evidence collected from previous interactions. By incorporating the dynamic feedback mechanism in the routing protocol, misbehaved nodes are identified and avoided to forward packets. In this way,misbehavior can be mitigated. Objective and Sub-tasks The primary objective of this thesis is to Investigate the state of the art of dynamic feedback mechanisms and protocols analyze, implement and evaluate DSR protocols to see how it improves the network performance and what are the side effects of introducing the mechanism to the mobile ad hoc network. Following tasks must be done to achieve the primary objective. Study the preliminary knowledge that is required to carry out the main tasks. For example, to understand DSR protocol one must have some knowledge of Bayesian analysis; to do performance analysis one must learn the methodologies of conducting performance analysis and processing simulation data. Investigate security issues of mobile ad hoc network and current dynamic feedback mechanisms or protocols that are used to solve or mitigate the issues. Investigate and learn how to use the network simulation tool. There are several popular network simulation tools available and we need to choose the one that best suits our needs. The selected network simulator should be studied so that we can use it as platform to implement protocol and conduct simulations. Analyze and implement the DSR protocol based on Dynamic Source Routing protocol (DSR); evaluate the network performance. Structure of the Report Since we have almost gone through the chapter one, we only briefly present the content of the subsequent chapters in this section. Preliminary Information State of the Art Analysis Design Implementation and Tests Performance Analysis Conclusion and Future Work Preliminary information we have introduced the MANET. This chapter presents other preliminary information and concepts that will be used in other parts of the thesis. Firstly four general modes of routing operations are introduced and compared. The DSR protocol, which is used as underlying routing protocol in the thesis, is explained in detail. Secondly Bayesian estimation and Beta function are explained to pave the way for the analysis of the reputation model of DSR in the chapter 4. Thirdly some techniques regarding simulation and performance analysis are presented. Finally, several popular network simulation tools are discussed and compared. Mobile Ad Hoc Network Routing Protocols Nowadays there are various routing protocols proposed for the MANET. The most popular ones are DSDV (Destination-Sequenced Distance Vector), TORA (Temporally- Ordered Routing Algorithm), DSR (Dynamic Source Routing) and AODV (Ad-hoc On Demand Distance Vector). These routing protocols can be categorized in different routing operation modes. Mode of Routing Operations These two modes concern whether or not nodes in an ad hoc network should keep track of routes to all possible destinations, or instead keep track of only those destinations of immediate interest Proactive protocols store route information even before it is needed. This kind of protocols has advantage that communications with arbitrary destination experience minimal delay. However it also suffers from the disadvantage that additional control traffic is needed to continually update stale route information. This could significantly increase routing overhead especially for the MANET where the links are often broken. Reactive protocols, on the contrary, acquire routing information only when it is actually needed. However, the latency of the communication increases tremendously especially when a node communicates to another at the first time. Source routing vs. Hop-by-hop routing These two modes concern whether the source node decides the route for a packet to be forwarded to the destination or the intermediate nodes are allowed to decide the next hop until the packet arrives at the destination. In the source routing protocols, the source node decides the route and puts the route information in the packet header. All the intermediate nodes forward the packet along the route faithfully. This kind of protocols has advantage that the intermediate nodes are not required to maintain the routing information. But it suffers from the disadvantage that the packet size grows because of source routing information carried in each packet. In the hop-by-hop routing protocols, it is sufficient for the source to know only how to get to the next hop and intermediate nodes find their own next-hops until the destination. In contrast to source routing protocols, hop-by-hop routing protocols do not increase packet size but they requires all the intermediate nodes to maintain rout ing information. Table 2-1 Categories of routing protocols has compared the performance of these four routing protocols . The results show that DSR has best throughput performance (above 95%) at all mobility rates and movement speeds. Thus we will use DSR as basic routing protocol in this thesis. The Dynamic Source Routing Protocol (DSR) John et al. proposed the dynamic source routing protocol (DSR) [1] which is a routing protocol for use in multi-hop wireless ad hoc networks of mobile nodes. DSR is an ondemand protocol, in which route are only discovered when data need to be transmitted to a node where no route has yet been discovered. The advantage of this on-demand routing protocol is that there are not any periodic routing advertisement and reducing the routing overhead. DSR is also a source routing protocol, allowing multiple routes to any destination and allows each sender to select and control the routes used in routing the packets. DSR is composed of the two main mechanisms: Route Discovery and Route Maintenance which are explained below. Route Discovery Route Discovery aims at finding routes from a source node to destination. Figure 2-1 illustrates the procedure of Route Discovery. When a source node S wants to send a data packet to some destination node D, it first searches its route cache to find whether there is a route to D. If there is no route to D, then S will initiate a Route Discovery and send out Route Request message which is propagated to all the nodes within its transmission range. At the mean time, it saves the data packet in its send buffer. The Route Request message contains the addresses of source node and destination node, a unique route request identifier and a route record which records all the intermediate nodes that this route request packet has traveled through. S appends itself to the beginning of the route record when it initiates the message. When a node receives the Route Request message, it compares the destination address in the message with its own address to judge whether itself is the destination node. If it is not, it will append its own address in the route record and propagate the message to other nodes. If the node is the destination node, it will send a Route Reply message to the source node and the message contains the source route record which is accumulated when the Route Request message is forwarded along its way to the destination. When the destination sends the Route Reply, if it uses MAC protocols such as IEEE 802.11 that require a bidirectional link, it just reverse the source route record and use it as route to send Route Reply to the source node. Otherwise it should find the route by searching its route cache or sending out a Route Request which piggybacks the Route Reply for the source node. When the source node receives the Route Reply message, it puts the returned route into its route cache. From t hen on all the packets destined to the same destination will use this route until it is broken. Route Maintenance Since the ad hoc network is dynamic and the topology of the network changes frequently, the existing routes maintained by nodes in their route cache are often broken. After forwarding a packet, a node must attempt to confirm the reachability of the next-hop node. If the node does not receive any confirmation from the next hop during a certain period of time, it will retransmit the packet. If after a maximum number of retransmission it still does not receive any confirmation, it will think the link to the next hop is broken and will send a Route Error message to the source node. DSR proposes three acknowledge mechanisms to confirm that data can flow over the link from that node to the next hop: Link-layer acknowledgement which is provided by MAC layer protocol such as IEEE 802.11. Passive acknowledgement in which a node hears the next-hop node forwarding the packet and thus confirms the reachability of the link. Network-layer acknowledgement in which a node sends an explicit acknowledgement request to its next-hop node. Passive Acknowledgement Passive Acknowledgement (PACK) is important in DSR protocol because it is used to detect whether the next hop forwards the packet or drops it. We explain it in detail in this section. Passive acknowledgement is used with the assumption that: Network links operates bi- directionally. The network interface is in the promiscuous mode. When a node taps a new packet in promiscuous mode after it originates or forwards a packet, it consider it as an acknowledgement of the first packet if both of following check success. The Source Address, Destination Address, Protocol, Identification, and Fragment Offset fields in the IP header of the two packets MUST match. If either packet contains a DSR Source Route header, both packets MUST contain one, and the value in the Segments Left field in the DSR Source Route header of the new packet MUST be less than that in the first packet. If no matched packet is found during PACK timeout, the node will consider the link between the next hop and itself is broken and will send Route Error message to the source node. Additional features DSR has additional features such as replying to route requests using cached routes, caching overheard routing information, packet salvaging and flow state extension and etc. We will introduce them in section 4.1 and discuss how they will impact the performance of network, how they will interact with DSR and whether they will be enabled in our simulation. Performance Analysis Techniques This section introduces the performance analysis techniques and methodologies that will be used in the performance evaluation. Factors and Primary Factors There are many parameters that will influence the simulation results and need to be carefully chosen in the simulations. Some parameters are chosen based on experience values or the conditions of the network we want to simulate. Others need to be tuned to optimize the network performance. We distinguish the two kinds of parameters as follows: Factors are the variables that affect the simulation result and have several alternatives. Normally they are decided based on experience. Primary factors are the factors whose effects need to be quantified. This kind of factors usually needs to be adjusted through simulation. Data Measurement The key step of the network performance analysis is to interpret the simulation result and summarize the characteristic of the network. To avoid the inaccurate simulation results due to an extreme scenario, we usually run simulations on several different scenarios. The data set of these simulations are called sample. A single number must be presented to give the key characteristic of the sample and this single number is called an average of the data. There are three alternatives to summarize a sample Mean is obtained by taking the sum of all observations and dividing this sum by the number of observations in the sample. Median is obtained by sorting the observations in an increasing order and taking the observation that is in the middle of series. If the number of the observations is even, the mean of the middle two values is used as a median. Mode is obtained by plotting a histogram and specifying the midpoint of the bucket where the histogram peaks. Confidence Interval for the Mean In our performance evaluation, the main objective is to compare the simulation results of DSR and Standard DSR to see whether there is any performance improvement. However, most simulation results are random in some degree due to the particularity of the node movement scenarios and we cannot tell whether the two systems are different. One way to minimize the random effect is to repeat the simulations with different scenarios as many times as possible and get a large sample space. Unfortunately, due to the time limitation we cannot conduct many simulations. points out that using confidence interval we can tell whether the two systems are different with smaller sample space. The confidence interval for the mean can be calculated using If the confidence intervals of the simulation results of the two systems have no overlap, then we can claim the two systems are different and one system is superior or inferior to the other. GloMoSims source and binary code can be downloaded only by academic institutions for research purposes. Commercial users must use QualNet, the commercial version of GloMoSim. OPNET Modeler OPNET Modeler is commercial network simulation environment for network modeling and simulation. It allows the users to design and study communication networks, devices, protocols, and applications with flexibility and scalability [30]. It simulates the network graphically and its graphical editors mirror the structure of actual networks and network components. The users can design the network model visually.The modeler uses object-oriented modeling approach. The nodes and protocols are modeled as classes with inheritance and specialization. The development language is C. Comparison When choosing a network simulator, we normally consider the accuracy of the simulator. Unfortunately there is no conclusion on which of the above three simulator is the most accurate one. David Cavin et al. has conducted experiments to compare the accuracy of the simulators and it finds out that the results are barely comparable [31]. Furthermore, it warns that no standalone simulations can fit all the needs of the wireless developers. It is more realistic to consider a hybrid approach in which only the lowest layers (MAC and physical layers) and the mobility model are simulated and all the upper layers (from transport to application layers) are executed on a dedicated hosts (e.g. cluster of machines). Although there is no definite conclusion about the accuracy of the three network simulators, we have to choose one of them as our simulation environment. We compare the simulators using some metrics and the results are summarized After comparing the three simulators, we decide to choose ns2 as network simulator in our thesis because Ns2 is open source free software. It can be easily downloaded and installed. The author of the thesis has used ns2 in another network related course and gotten familiar with the simulation. Ns2 uses TCL and C++ as development languages for which the author has some programming experience. The author of the DSR protocol has conducted simulation on GloMoSim and gotten performance results. We want to do the simulation on a different simulation to form comparison. State of the Art In this chapter we will introduce the start of the art security solutions in MANET with emphasis on dynamic feedback mechanisms. Firstly, we will present the general security issues/requirements of MANET to pave the way for the future investigation. Then we will discuss the state of the art security mechanisms for MANET such as payment system,trust management system, reputation system, etc. Finally, we will summarize all the security solutions we discussed in this chapter. Security Issues in Mobile Ad Hoc Network Due to lack of central infrastructural and wireless links susceptible to attacks, security in ad hoc network has inherent weakness. In section 1.2 we have discussed the reasons why mobile ad hoc network imposes security challenges that cannot be solved by traditional security mechanisms. In this section, we present the general security properties required by ad hoc network. Following are general security properties regarding ad hoc network Confidentiality: The confdiantiality property is to protect certain information from unauthorized disclosure. The information includes not only the application data that send over the routing protocol, but also the routing information itself as well as network topology and geographical location. Integrity: The integrity ensures that the transmitted message and other system asset are modified only by authorized parties. In the routing level, it requires all nodes in the network following correct routing procedure. The main challenge of ensuring integrity is that without central infrastructure and powerful computing capabilities, it is difficult to apply existing cryptography and key management systems. Availability: The availability property requires that the services or devices are exempt from denial of service, which is normally done by interruption, network or server overload. Typical examples or denial of service attack are radio jamming, in which a misbehaved node transmit radio to interference other nodes communications, and battery exhaustion, in which a misbehaved node interact with a node for no other purpose than to consume its battery energy. Authentication: The authentication property requires that the communication entitys identification is recognized and proved before communication starts. Access control: This property requires restricting resources, services or data to special identities according to their access rights or group membership. Non-repudiation: This property ensures that when data are sent from sender to receiver, the sender cannot deny that he has sent the data and the receiver cannot deny that he has received the data. Mobile nodes may conduct different misbehavior for different purposes. Po-Wah Yau classifies the misbehaved nodes into following categories. Failed nodes are simply those unable to perform an operation; this could be because power failure and environmental events. Badly failed nodes exhibit features of failed nodes but they can also send false routing messages which are a threat to the integrity of the network. Selfish nodes are typified by their unwillingness to cooperate as the protocol requires whenever there is a personal cost involved. Packet dropping is the main attack by selfish nodes. Malicious nodes aim to deliberately disrupt the correct operation of the routing protocol, denying network service if possible. These four types of misbehaved nodes actually can be categorized in two aspects: whether their misbehaviors are intentional or unintentional, and the severity of the results. Payment Systems Payment systems provide economic incentives for the cooperation in MANET. They consider that each node in MANET is its own authority and tries to maximize the benefits it gets from the network. Thus each node tends to be selfish, dropping packets not destined to them but make use of other nodes to forward their own packets. The purpose of payment systems is to encourage the cooperation within the MANET by economic incentives. There are several variations of payment systems proposed. Nuglets Nuglets is a virtual currency mechanism for charging (rewarding) server usage (provision). Nodes that use a service must pay for it (in nuglets) to nodes that provide the service. A typical service is packet forwarding which is provided by intermediate nodes to the source and the destination of the packet. Therefore either the source or the destination should pay for it. There are two models for charging for the packet forwarding service: the Packet Purse Model (PPM) and the Packet Trade Model (PTM). In the Packet Purse Model, the sender pays for the packet. It loads the packet with a number of nuglets when sending the packet. Each intermediate forwarding node acquires some nuglets from the packet that covers its forwarding costs. If a packet does not have enough nuglets to be forwarded, then it is discarded. If there are nuglets left in the packet once it reaches destination, the nuglets are lost. In the Packet Trade Model, the destination pays for the packet. Each intermediate node buys the packet from previous one for some nuglets and sells it to the next one for more nuglets until the destination buys it. Either of the two models has advantages and disadvantages. While the Packet Purse Model deters nodes from sending useless data and avoids the network overloading, the Packet Trade Model can lead to an overload of the network and the destination receives packets it does not want. On the other hand, in the Packet Purse Model it is difficult to estimate the number of nuglets th at are required to reach a given destination. But thePacket Purse Model does not need to consider this problem. To take advantages of the two models and avoid the disadvantages, a hybrid model is suggested. In this model, the sender loads the packet with some nuglets before sending it.The packet is handled according to the Packet Purse Model until it runs out of nuglets. Then it is handled according to the Packet Trade Model until the destination buys it. Counter To address the problems encountered by the nuglets approach such as difficulty in estimating pre-load nuglets and possible network overload, another payment approach based on credit counter is suggested. In this approach, the current state of each node is described by two variables b and c, where b is the remaining battery power and cstands for the value of its nuglet counter. More precisely, b is the number of packets that the node can send using its remaining energy and c is the number of packets a node canoriginate. A node can originate a number of packets N only when the condition c=N holds. When a node forwards a packet, nuglet counter c is increased by one and b is reduced by one. Thus in order to originate packets, each node must earn credits by forwarding packets. The counter solution requires tamper resistant hardware security module. Spirit S. Zhong et al. proposed Sprite [19], a credit-based system for MANET. As opposed to Nuglets or Counter they do not require tamper-proof hardware to prevent the fabrication of payment units. Instead, they introduce a central Credit Clearance Service (CCS). The basic scheme of the system is as follows. When a node receives a message the node keeps a receipt of the message and reports to the CCS when the node has a fast connection to Credit Clearance Service (CCS). The CCS then determines the charge and credits to each node involved in the transmission of a message, depending on the reported receipts of a message. In this scheme, the sender charges money. A node that has forwarded a message is compensated, but the credit that a node receives depends on whether or not its forwarding action is successful. Forwarding is considered successful if and only if the next node on the path reports a valid receipt to the CCS. Discussion on the Payment Systems The payment systems we describe in above sections either assumes a tamper resistant hardware module is available to ensure that the behavior of the node is not modified or requires a central authority server to determine the charge and credit to each node involved in the transmission of a message. Tamper resistant hardware may not be appropriate for most mobile devices because it demands advanced hardware solution and increases the cost of the devices. Lacking of central authority server is right the inherent property of MANET that causes security challenges so it is also not appropriate. Furthermore, all the approaches described above suffer from locality problems [20] that nodes in different locations of the network will have different chances for earning virtualcurrency, which may not be fair for all nodes. Usually nodes at the periphery of the network will have less chance to be rewarded. Reputation System Reputation systems have emerged as a way to reduce the risk entailed in interactions among total strangers in electronic marketplace. Centralized reputation systems have been adopted by many on-line electronic auctions such as eBay to collect and store reputation ratings from feedback providers in a centralized reputation database. Decentralized reputation systems used by MANET, on the other hand, do not use centralized reputation database. Instead, in these reputation systems, each node keeps the ratings about other node and updating the ratings by direct observation of the behaviorsof neighboring nodes or second hand information from other trusted nodes. Identifies three goals for reputation systems: To provide information to distinguish between a trust-worthy principal and an untrustworthy principals. To encourage principals to act in a trustworthy manner To discourage untrustworthy principals from participating in the service the reputation mechanism is present to protect. Most of the reputation systems in MANET are based on trust management system. Trust is such a subjective and dynamic concept that different entities can hold different opinions on it even while facing the same situation. Trust management system can work without reputation system. For example, a mobile node can form opinion about other nodes by direct experience with the nodes.We can unify reputation system and trust management system to dynamic feedback mechanisms. Former one is a global reputation system and mobile nodes share their own experiences of interaction with other nodes. The later one is a local reputation system in which mobile nodes rating the trustability of other nodes based on its own observation. DSR DSR is a reputation system aiming at coping with misbehavior in MANET. The idea is to detect the misbehaved nodes and isolate them fromcommunication by not using them for routing and forwarding and by not allowing the misbehaved nodes to use itself to forward packets. DSR stands for Cooperation Of Nodes: Fairness In Dynamic Ad-hoc Network. It usually works as an extension to on demand routing Mobile Ad Hoc Networks (MANETs) Mobile Ad Hoc Networks (MANETs) Introduction What is Mobile Ad Hoc Network? With rapid development of wireless technology, the Mobile Ad Hoc Network (MANET) has emerged as a new type of wireless network. MANET is a collection of wireless mobile nodes (e.g. laptops) that dynamically function as a network without the use of any existing infrastructure and centralized administration. It is an autonomous system where each node operates not only as an end system but also as a router to forward packets for other nodes. Since the nodes in MANET move around, the wireless links break and re-establish frequently. Furthermore, most of mobile nodes are resource limited in computing capability and battery power and therefore traditional computing content routing protocols are not suitable for MANET. Several ad hoc routing protocols have been proposed for each node acting as router and maintaining routing information. There are many other applications of MANET. For examples, MANET can be used to provide emergency Services when the network is impaired due to the damaging of existing infrastructure [8]. Computer scientists have predicted a world of ubiquitous computing in which computers will be all around us, constantly performing mundane tasks to make our lives a little easier. These ubiquitous computers connect in mobile ad hoc mode and change the environment or react to the change of the environment where they are suited. MANET is also found useful in the so-called sensor dust network to coordinate the activities and reports of a large collection of tiny sensor devices which could offer detailed information about terrain or environmental dangerous conditions. Problem Statement and Motivation Most current ad hoc routing protocols assume that the wireless network is benign and every node in the network strictly follows the routing behavior and is willing to forward packets for other nodes. Most of these protocols cope well with the dynamically changing topology. However, they do not address the problems when misbehavior nodes present in the network.A commonly observed misbehavior is packet dropping. In a practical MANET, most devices have very limited computing and battery power while packet forwarding consumes a lot of such resources. Thus some of the mobile devices would not like to forward the packets for the benefit of others and they drop packets not destined to them. On the other hand, they still make use of other nodes to forward packets that they originate. These misbehaved nodes are very difficult to identify because we cannot tell that whether the packets are dropped intentionally by the misbehaved nodes or dropped due to the node having moved out of transmission range or other link error. Packet drop significantly decreases the network performance.Traditional security mechanisms are generally not suitable for MANET because: The network lacks central infrastructure to apply traditional security mechanism such as access control, authentication and trusted third party. Limited bandwidth, battery lifetime, and computation power prohibits the deployment of complex routing protocols or encryption algorithms. New security models or mechanisms suitable for MANET must be found. Network topologies and memberships are constantly changing. Thus new intrusion detection system and entity recognition mechanisms that are suitable for mobile ad hoc networks must be designed to avoid or mitigate the behavior to the networks. Trust management systems have been recently introduced as a security mechanism in MANET. In a trust management system, a communicating entity collects evidence regarding competence, honesty or security of other network participants with the purpose of making assessment or decisions regarding their trust relationships. Here trust Objective and Sub-tasks means the confidence of an entity on another entity based on the expectation that the other entity will perform a particular action important to the trustor, irrespective of the ability to monitor or control that other entity . For example, a trust-based routing protocol can collect the evidence of nodes misbehaving, form trust values of the nodes and select safest routes based on the trust metrics.Reputations systems are often seen as a derivation of trust management system. In the reputation system, an entity forms its trust on another entity based not only on the selfobserved evidence but also on the second hand information from third parties. One of the influential reputation systems is the DSR protocol. In the trust management system, reputation system and other trust-based systems, route selection is based on the sending nodes prior experience with other nodes in the network. Its opinions about how other entities are honest are constantly changing. Thus, we call the trust manag ement systems and their derivations as dynamic feedback mechanisms. The dynamic feedback mechanisms are usually applied on the current ad hoc routing protocols to rate the trust about other nodes in the network and make routing decisions based on the trust matrix, which is formed according to the evidence collected from previous interactions. By incorporating the dynamic feedback mechanism in the routing protocol, misbehaved nodes are identified and avoided to forward packets. In this way,misbehavior can be mitigated. Objective and Sub-tasks The primary objective of this thesis is to Investigate the state of the art of dynamic feedback mechanisms and protocols analyze, implement and evaluate DSR protocols to see how it improves the network performance and what are the side effects of introducing the mechanism to the mobile ad hoc network. Following tasks must be done to achieve the primary objective. Study the preliminary knowledge that is required to carry out the main tasks. For example, to understand DSR protocol one must have some knowledge of Bayesian analysis; to do performance analysis one must learn the methodologies of conducting performance analysis and processing simulation data. Investigate security issues of mobile ad hoc network and current dynamic feedback mechanisms or protocols that are used to solve or mitigate the issues. Investigate and learn how to use the network simulation tool. There are several popular network simulation tools available and we need to choose the one that best suits our needs. The selected network simulator should be studied so that we can use it as platform to implement protocol and conduct simulations. Analyze and implement the DSR protocol based on Dynamic Source Routing protocol (DSR); evaluate the network performance. Structure of the Report Since we have almost gone through the chapter one, we only briefly present the content of the subsequent chapters in this section. Preliminary Information State of the Art Analysis Design Implementation and Tests Performance Analysis Conclusion and Future Work Preliminary information we have introduced the MANET. This chapter presents other preliminary information and concepts that will be used in other parts of the thesis. Firstly four general modes of routing operations are introduced and compared. The DSR protocol, which is used as underlying routing protocol in the thesis, is explained in detail. Secondly Bayesian estimation and Beta function are explained to pave the way for the analysis of the reputation model of DSR in the chapter 4. Thirdly some techniques regarding simulation and performance analysis are presented. Finally, several popular network simulation tools are discussed and compared. Mobile Ad Hoc Network Routing Protocols Nowadays there are various routing protocols proposed for the MANET. The most popular ones are DSDV (Destination-Sequenced Distance Vector), TORA (Temporally- Ordered Routing Algorithm), DSR (Dynamic Source Routing) and AODV (Ad-hoc On Demand Distance Vector). These routing protocols can be categorized in different routing operation modes. Mode of Routing Operations These two modes concern whether or not nodes in an ad hoc network should keep track of routes to all possible destinations, or instead keep track of only those destinations of immediate interest Proactive protocols store route information even before it is needed. This kind of protocols has advantage that communications with arbitrary destination experience minimal delay. However it also suffers from the disadvantage that additional control traffic is needed to continually update stale route information. This could significantly increase routing overhead especially for the MANET where the links are often broken. Reactive protocols, on the contrary, acquire routing information only when it is actually needed. However, the latency of the communication increases tremendously especially when a node communicates to another at the first time. Source routing vs. Hop-by-hop routing These two modes concern whether the source node decides the route for a packet to be forwarded to the destination or the intermediate nodes are allowed to decide the next hop until the packet arrives at the destination. In the source routing protocols, the source node decides the route and puts the route information in the packet header. All the intermediate nodes forward the packet along the route faithfully. This kind of protocols has advantage that the intermediate nodes are not required to maintain the routing information. But it suffers from the disadvantage that the packet size grows because of source routing information carried in each packet. In the hop-by-hop routing protocols, it is sufficient for the source to know only how to get to the next hop and intermediate nodes find their own next-hops until the destination. In contrast to source routing protocols, hop-by-hop routing protocols do not increase packet size but they requires all the intermediate nodes to maintain rout ing information. Table 2-1 Categories of routing protocols has compared the performance of these four routing protocols . The results show that DSR has best throughput performance (above 95%) at all mobility rates and movement speeds. Thus we will use DSR as basic routing protocol in this thesis. The Dynamic Source Routing Protocol (DSR) John et al. proposed the dynamic source routing protocol (DSR) [1] which is a routing protocol for use in multi-hop wireless ad hoc networks of mobile nodes. DSR is an ondemand protocol, in which route are only discovered when data need to be transmitted to a node where no route has yet been discovered. The advantage of this on-demand routing protocol is that there are not any periodic routing advertisement and reducing the routing overhead. DSR is also a source routing protocol, allowing multiple routes to any destination and allows each sender to select and control the routes used in routing the packets. DSR is composed of the two main mechanisms: Route Discovery and Route Maintenance which are explained below. Route Discovery Route Discovery aims at finding routes from a source node to destination. Figure 2-1 illustrates the procedure of Route Discovery. When a source node S wants to send a data packet to some destination node D, it first searches its route cache to find whether there is a route to D. If there is no route to D, then S will initiate a Route Discovery and send out Route Request message which is propagated to all the nodes within its transmission range. At the mean time, it saves the data packet in its send buffer. The Route Request message contains the addresses of source node and destination node, a unique route request identifier and a route record which records all the intermediate nodes that this route request packet has traveled through. S appends itself to the beginning of the route record when it initiates the message. When a node receives the Route Request message, it compares the destination address in the message with its own address to judge whether itself is the destination node. If it is not, it will append its own address in the route record and propagate the message to other nodes. If the node is the destination node, it will send a Route Reply message to the source node and the message contains the source route record which is accumulated when the Route Request message is forwarded along its way to the destination. When the destination sends the Route Reply, if it uses MAC protocols such as IEEE 802.11 that require a bidirectional link, it just reverse the source route record and use it as route to send Route Reply to the source node. Otherwise it should find the route by searching its route cache or sending out a Route Request which piggybacks the Route Reply for the source node. When the source node receives the Route Reply message, it puts the returned route into its route cache. From t hen on all the packets destined to the same destination will use this route until it is broken. Route Maintenance Since the ad hoc network is dynamic and the topology of the network changes frequently, the existing routes maintained by nodes in their route cache are often broken. After forwarding a packet, a node must attempt to confirm the reachability of the next-hop node. If the node does not receive any confirmation from the next hop during a certain period of time, it will retransmit the packet. If after a maximum number of retransmission it still does not receive any confirmation, it will think the link to the next hop is broken and will send a Route Error message to the source node. DSR proposes three acknowledge mechanisms to confirm that data can flow over the link from that node to the next hop: Link-layer acknowledgement which is provided by MAC layer protocol such as IEEE 802.11. Passive acknowledgement in which a node hears the next-hop node forwarding the packet and thus confirms the reachability of the link. Network-layer acknowledgement in which a node sends an explicit acknowledgement request to its next-hop node. Passive Acknowledgement Passive Acknowledgement (PACK) is important in DSR protocol because it is used to detect whether the next hop forwards the packet or drops it. We explain it in detail in this section. Passive acknowledgement is used with the assumption that: Network links operates bi- directionally. The network interface is in the promiscuous mode. When a node taps a new packet in promiscuous mode after it originates or forwards a packet, it consider it as an acknowledgement of the first packet if both of following check success. The Source Address, Destination Address, Protocol, Identification, and Fragment Offset fields in the IP header of the two packets MUST match. If either packet contains a DSR Source Route header, both packets MUST contain one, and the value in the Segments Left field in the DSR Source Route header of the new packet MUST be less than that in the first packet. If no matched packet is found during PACK timeout, the node will consider the link between the next hop and itself is broken and will send Route Error message to the source node. Additional features DSR has additional features such as replying to route requests using cached routes, caching overheard routing information, packet salvaging and flow state extension and etc. We will introduce them in section 4.1 and discuss how they will impact the performance of network, how they will interact with DSR and whether they will be enabled in our simulation. Performance Analysis Techniques This section introduces the performance analysis techniques and methodologies that will be used in the performance evaluation. Factors and Primary Factors There are many parameters that will influence the simulation results and need to be carefully chosen in the simulations. Some parameters are chosen based on experience values or the conditions of the network we want to simulate. Others need to be tuned to optimize the network performance. We distinguish the two kinds of parameters as follows: Factors are the variables that affect the simulation result and have several alternatives. Normally they are decided based on experience. Primary factors are the factors whose effects need to be quantified. This kind of factors usually needs to be adjusted through simulation. Data Measurement The key step of the network performance analysis is to interpret the simulation result and summarize the characteristic of the network. To avoid the inaccurate simulation results due to an extreme scenario, we usually run simulations on several different scenarios. The data set of these simulations are called sample. A single number must be presented to give the key characteristic of the sample and this single number is called an average of the data. There are three alternatives to summarize a sample Mean is obtained by taking the sum of all observations and dividing this sum by the number of observations in the sample. Median is obtained by sorting the observations in an increasing order and taking the observation that is in the middle of series. If the number of the observations is even, the mean of the middle two values is used as a median. Mode is obtained by plotting a histogram and specifying the midpoint of the bucket where the histogram peaks. Confidence Interval for the Mean In our performance evaluation, the main objective is to compare the simulation results of DSR and Standard DSR to see whether there is any performance improvement. However, most simulation results are random in some degree due to the particularity of the node movement scenarios and we cannot tell whether the two systems are different. One way to minimize the random effect is to repeat the simulations with different scenarios as many times as possible and get a large sample space. Unfortunately, due to the time limitation we cannot conduct many simulations. points out that using confidence interval we can tell whether the two systems are different with smaller sample space. The confidence interval for the mean can be calculated using If the confidence intervals of the simulation results of the two systems have no overlap, then we can claim the two systems are different and one system is superior or inferior to the other. GloMoSims source and binary code can be downloaded only by academic institutions for research purposes. Commercial users must use QualNet, the commercial version of GloMoSim. OPNET Modeler OPNET Modeler is commercial network simulation environment for network modeling and simulation. It allows the users to design and study communication networks, devices, protocols, and applications with flexibility and scalability [30]. It simulates the network graphically and its graphical editors mirror the structure of actual networks and network components. The users can design the network model visually.The modeler uses object-oriented modeling approach. The nodes and protocols are modeled as classes with inheritance and specialization. The development language is C. Comparison When choosing a network simulator, we normally consider the accuracy of the simulator. Unfortunately there is no conclusion on which of the above three simulator is the most accurate one. David Cavin et al. has conducted experiments to compare the accuracy of the simulators and it finds out that the results are barely comparable [31]. Furthermore, it warns that no standalone simulations can fit all the needs of the wireless developers. It is more realistic to consider a hybrid approach in which only the lowest layers (MAC and physical layers) and the mobility model are simulated and all the upper layers (from transport to application layers) are executed on a dedicated hosts (e.g. cluster of machines). Although there is no definite conclusion about the accuracy of the three network simulators, we have to choose one of them as our simulation environment. We compare the simulators using some metrics and the results are summarized After comparing the three simulators, we decide to choose ns2 as network simulator in our thesis because Ns2 is open source free software. It can be easily downloaded and installed. The author of the thesis has used ns2 in another network related course and gotten familiar with the simulation. Ns2 uses TCL and C++ as development languages for which the author has some programming experience. The author of the DSR protocol has conducted simulation on GloMoSim and gotten performance results. We want to do the simulation on a different simulation to form comparison. State of the Art In this chapter we will introduce the start of the art security solutions in MANET with emphasis on dynamic feedback mechanisms. Firstly, we will present the general security issues/requirements of MANET to pave the way for the future investigation. Then we will discuss the state of the art security mechanisms for MANET such as payment system,trust management system, reputation system, etc. Finally, we will summarize all the security solutions we discussed in this chapter. Security Issues in Mobile Ad Hoc Network Due to lack of central infrastructural and wireless links susceptible to attacks, security in ad hoc network has inherent weakness. In section 1.2 we have discussed the reasons why mobile ad hoc network imposes security challenges that cannot be solved by traditional security mechanisms. In this section, we present the general security properties required by ad hoc network. Following are general security properties regarding ad hoc network Confidentiality: The confdiantiality property is to protect certain information from unauthorized disclosure. The information includes not only the application data that send over the routing protocol, but also the routing information itself as well as network topology and geographical location. Integrity: The integrity ensures that the transmitted message and other system asset are modified only by authorized parties. In the routing level, it requires all nodes in the network following correct routing procedure. The main challenge of ensuring integrity is that without central infrastructure and powerful computing capabilities, it is difficult to apply existing cryptography and key management systems. Availability: The availability property requires that the services or devices are exempt from denial of service, which is normally done by interruption, network or server overload. Typical examples or denial of service attack are radio jamming, in which a misbehaved node transmit radio to interference other nodes communications, and battery exhaustion, in which a misbehaved node interact with a node for no other purpose than to consume its battery energy. Authentication: The authentication property requires that the communication entitys identification is recognized and proved before communication starts. Access control: This property requires restricting resources, services or data to special identities according to their access rights or group membership. Non-repudiation: This property ensures that when data are sent from sender to receiver, the sender cannot deny that he has sent the data and the receiver cannot deny that he has received the data. Mobile nodes may conduct different misbehavior for different purposes. Po-Wah Yau classifies the misbehaved nodes into following categories. Failed nodes are simply those unable to perform an operation; this could be because power failure and environmental events. Badly failed nodes exhibit features of failed nodes but they can also send false routing messages which are a threat to the integrity of the network. Selfish nodes are typified by their unwillingness to cooperate as the protocol requires whenever there is a personal cost involved. Packet dropping is the main attack by selfish nodes. Malicious nodes aim to deliberately disrupt the correct operation of the routing protocol, denying network service if possible. These four types of misbehaved nodes actually can be categorized in two aspects: whether their misbehaviors are intentional or unintentional, and the severity of the results. Payment Systems Payment systems provide economic incentives for the cooperation in MANET. They consider that each node in MANET is its own authority and tries to maximize the benefits it gets from the network. Thus each node tends to be selfish, dropping packets not destined to them but make use of other nodes to forward their own packets. The purpose of payment systems is to encourage the cooperation within the MANET by economic incentives. There are several variations of payment systems proposed. Nuglets Nuglets is a virtual currency mechanism for charging (rewarding) server usage (provision). Nodes that use a service must pay for it (in nuglets) to nodes that provide the service. A typical service is packet forwarding which is provided by intermediate nodes to the source and the destination of the packet. Therefore either the source or the destination should pay for it. There are two models for charging for the packet forwarding service: the Packet Purse Model (PPM) and the Packet Trade Model (PTM). In the Packet Purse Model, the sender pays for the packet. It loads the packet with a number of nuglets when sending the packet. Each intermediate forwarding node acquires some nuglets from the packet that covers its forwarding costs. If a packet does not have enough nuglets to be forwarded, then it is discarded. If there are nuglets left in the packet once it reaches destination, the nuglets are lost. In the Packet Trade Model, the destination pays for the packet. Each intermediate node buys the packet from previous one for some nuglets and sells it to the next one for more nuglets until the destination buys it. Either of the two models has advantages and disadvantages. While the Packet Purse Model deters nodes from sending useless data and avoids the network overloading, the Packet Trade Model can lead to an overload of the network and the destination receives packets it does not want. On the other hand, in the Packet Purse Model it is difficult to estimate the number of nuglets th at are required to reach a given destination. But thePacket Purse Model does not need to consider this problem. To take advantages of the two models and avoid the disadvantages, a hybrid model is suggested. In this model, the sender loads the packet with some nuglets before sending it.The packet is handled according to the Packet Purse Model until it runs out of nuglets. Then it is handled according to the Packet Trade Model until the destination buys it. Counter To address the problems encountered by the nuglets approach such as difficulty in estimating pre-load nuglets and possible network overload, another payment approach based on credit counter is suggested. In this approach, the current state of each node is described by two variables b and c, where b is the remaining battery power and cstands for the value of its nuglet counter. More precisely, b is the number of packets that the node can send using its remaining energy and c is the number of packets a node canoriginate. A node can originate a number of packets N only when the condition c=N holds. When a node forwards a packet, nuglet counter c is increased by one and b is reduced by one. Thus in order to originate packets, each node must earn credits by forwarding packets. The counter solution requires tamper resistant hardware security module. Spirit S. Zhong et al. proposed Sprite [19], a credit-based system for MANET. As opposed to Nuglets or Counter they do not require tamper-proof hardware to prevent the fabrication of payment units. Instead, they introduce a central Credit Clearance Service (CCS). The basic scheme of the system is as follows. When a node receives a message the node keeps a receipt of the message and reports to the CCS when the node has a fast connection to Credit Clearance Service (CCS). The CCS then determines the charge and credits to each node involved in the transmission of a message, depending on the reported receipts of a message. In this scheme, the sender charges money. A node that has forwarded a message is compensated, but the credit that a node receives depends on whether or not its forwarding action is successful. Forwarding is considered successful if and only if the next node on the path reports a valid receipt to the CCS. Discussion on the Payment Systems The payment systems we describe in above sections either assumes a tamper resistant hardware module is available to ensure that the behavior of the node is not modified or requires a central authority server to determine the charge and credit to each node involved in the transmission of a message. Tamper resistant hardware may not be appropriate for most mobile devices because it demands advanced hardware solution and increases the cost of the devices. Lacking of central authority server is right the inherent property of MANET that causes security challenges so it is also not appropriate. Furthermore, all the approaches described above suffer from locality problems [20] that nodes in different locations of the network will have different chances for earning virtualcurrency, which may not be fair for all nodes. Usually nodes at the periphery of the network will have less chance to be rewarded. Reputation System Reputation systems have emerged as a way to reduce the risk entailed in interactions among total strangers in electronic marketplace. Centralized reputation systems have been adopted by many on-line electronic auctions such as eBay to collect and store reputation ratings from feedback providers in a centralized reputation database. Decentralized reputation systems used by MANET, on the other hand, do not use centralized reputation database. Instead, in these reputation systems, each node keeps the ratings about other node and updating the ratings by direct observation of the behaviorsof neighboring nodes or second hand information from other trusted nodes. Identifies three goals for reputation systems: To provide information to distinguish between a trust-worthy principal and an untrustworthy principals. To encourage principals to act in a trustworthy manner To discourage untrustworthy principals from participating in the service the reputation mechanism is present to protect. Most of the reputation systems in MANET are based on trust management system. Trust is such a subjective and dynamic concept that different entities can hold different opinions on it even while facing the same situation. Trust management system can work without reputation system. For example, a mobile node can form opinion about other nodes by direct experience with the nodes.We can unify reputation system and trust management system to dynamic feedback mechanisms. Former one is a global reputation system and mobile nodes share their own experiences of interaction with other nodes. The later one is a local reputation system in which mobile nodes rating the trustability of other nodes based on its own observation. DSR DSR is a reputation system aiming at coping with misbehavior in MANET. The idea is to detect the misbehaved nodes and isolate them fromcommunication by not using them for routing and forwarding and by not allowing the misbehaved nodes to use itself to forward packets. DSR stands for Cooperation Of Nodes: Fairness In Dynamic Ad-hoc Network. It usually works as an extension to on demand routing

Nora Helmer in Ibsens A Doll House Essay -- A Doll’s House Essays

In 1879, Henrik Ibsen published the play A Dolls House. However, to much of his displeasure the portrayal of the third act was considered erroneous to critics and audiences of that time frame. This controversy centered on the play’s conclusion in Nora's decision to leave her marriage and abandon her children. Critics labeled this decision appalling and unrealistic, since at that time in history no true woman would ever make such a choice. This uproar forced Ibsen to write a second ending where Nora instead decides that the children need her more than she needs her freedom. Thus, leaving critics and audiences contently satisfied. Since then, though times have changed and ideas and beliefs of the past have been altered, maybe the critics had it right about Nora’s departure. Perhaps Ibsen’s original ending is better left unsaid. Therefore, other than the alternative ending that Ibsen produced, how might the character of Nora deal with the situation at hand differently, based on what can be determined about her from the text? For starters, how about confronting the title of the story? Just who is the Doll? Many may claim that the doll is automatically Nora, for the reasons that she has been molded by her father and then toyed around with by her husband. To those individuals, Nora may seem like she is the victim, the poor little girl who can not comprehend who she is, the sweet â€Å"sky-lark† who had to leave her family for the findings of her true inner being†¦Or on a different note, Nora is the master and the controller of all that is functioning in the Helmer household. Although her husband, Torvald, may refer to her as a sky-lark, squirrel, or singing bird, it can be viewed in the text that Nora does not object to these remarks but r... ...a man who loves her and abandoning her children. Point in taking: Nora served no sense of accomplishment and only declared her egotism in a single selfish act. In the end, Nora’s greatest strength became her greatest weakness and it lead to her vindicated defeat. If only Nora used her powerful gift of control to step up to society instead of blocking it out, would she been able to save herself, her family, and her characters reputation as a feminine heroine, instead of a controversial role. But perhaps the controversy over Nora’s character is what we cherish so deeply because it is beyond our understanding. The idea that she is someone who is eternally captivating but can never fully be defined completely. Works Cited Kennedy, X.J. and Gioia, Dana. Backpack Literature: An Introduction to Fiction, Poetry, and Drama. New York: Pearson Longman, 2006. 778-843. Nora Helmer in Ibsen's A Doll House Essay -- A Doll’s House Essays In 1879, Henrik Ibsen published the play A Dolls House. However, to much of his displeasure the portrayal of the third act was considered erroneous to critics and audiences of that time frame. This controversy centered on the play’s conclusion in Nora's decision to leave her marriage and abandon her children. Critics labeled this decision appalling and unrealistic, since at that time in history no true woman would ever make such a choice. This uproar forced Ibsen to write a second ending where Nora instead decides that the children need her more than she needs her freedom. Thus, leaving critics and audiences contently satisfied. Since then, though times have changed and ideas and beliefs of the past have been altered, maybe the critics had it right about Nora’s departure. Perhaps Ibsen’s original ending is better left unsaid. Therefore, other than the alternative ending that Ibsen produced, how might the character of Nora deal with the situation at hand differently, based on what can be determined about her from the text? For starters, how about confronting the title of the story? Just who is the Doll? Many may claim that the doll is automatically Nora, for the reasons that she has been molded by her father and then toyed around with by her husband. To those individuals, Nora may seem like she is the victim, the poor little girl who can not comprehend who she is, the sweet â€Å"sky-lark† who had to leave her family for the findings of her true inner being†¦Or on a different note, Nora is the master and the controller of all that is functioning in the Helmer household. Although her husband, Torvald, may refer to her as a sky-lark, squirrel, or singing bird, it can be viewed in the text that Nora does not object to these remarks but r... ...a man who loves her and abandoning her children. Point in taking: Nora served no sense of accomplishment and only declared her egotism in a single selfish act. In the end, Nora’s greatest strength became her greatest weakness and it lead to her vindicated defeat. If only Nora used her powerful gift of control to step up to society instead of blocking it out, would she been able to save herself, her family, and her characters reputation as a feminine heroine, instead of a controversial role. But perhaps the controversy over Nora’s character is what we cherish so deeply because it is beyond our understanding. The idea that she is someone who is eternally captivating but can never fully be defined completely. Works Cited Kennedy, X.J. and Gioia, Dana. Backpack Literature: An Introduction to Fiction, Poetry, and Drama. New York: Pearson Longman, 2006. 778-843.

A Pragmatic Approach for Comparative Analysis of Linear and Rotary Generators :: Essays Papers

A Pragmatic Approach for Comparative Analysis of Linear and Rotary Generators ABSTRACT This paper identifies the need for consolidating analysis techniques for the purpose of designing linear electrical generation systems. Additionally, it identifies a need for concise system development tools that help designers make practical comparisons between linear and rotary machines. INTRODUCTION The basic principles for converting mechanical energy to electrical energy have been known for over a century. It would seem that after this much time, advancements in electrical generation should have reached their limits; however, up to the late 1980’s and early 90’s the use of linear generators for the generation of electricity has not been seriously considered [1] [4]. Linear generators and motors are classified as linear motion electromagnetic systems (LMESs) [1]. LMESs that are used as electric generators function by directly utilizing the translational (back and forth or up and down) thrust from mechanical systems to generate electricity as opposed to the more conventional generation approach of rotational mechanical energy conversion. For an engineer to determine the feasibility of using a linear electric generator in a system’s design many comparisons between rotary and linear machines must be made. Several points to consider when making this comparison include: practicality of using linear power generation for that particular system, cost to build and design, total system efficiency, role of modern day power electronics, type of driving force (linear or rotational) applied to the generator system, system power factor, force density and force ripple on the drive components, cost to maintain, and the system’s reliability. The relative weights of these considerations will vary from one system to the next. The motivation behind this question was the decision on whether to use a linear or rotary generator on a buoy driven, ocean wave electrical generator project [6]. During this decision process, many opinions and assumptions between these competing systems were made, but finding hard data that compa red the two methods was not readily available. Taking the time to thoroughly evaluate the electrical and mechanical technical aspects of this choice (rotary vs. linear) conflicted with the tight scheduling requirements of the project. This situation forced the team to make a best approximation based on limited experience instead of a deliberate and thoroughly evaluated approach. WHY LINEAR GENERATORS ARE USED Electrical energy generation is being expanded by creative innovation, and linear generators are a large part of this trend.

Mainstream Media hegemony and new media environment Essay

(Ex- Deputy Controller, Head of current Affair National Broadcasting Service Radio Pakistan, Bureau chief mediacon international, member CMA,, Community Media Association, UK), published author ezine and upublish.com) Pakistan’s mainstream media outlets have perhaps misunderstand the meaning of free flow of information under the freedom of press law. Perhaps they are not aware of the consequences which are being faced by top notch mainstream media across the so-called civilized word. In Pakistan many media groups reporting without realizing its impact on our socio-economic environment and deep rooted cultural impact. We have seen in past that misreporting by print and electronic mainstream media regarding shia-sunni conflicts created anger and anxiety amongst different sects led to horrible sectarian violence. Beside, reporting regarding terrorist attacks and rape case are arrogantly presented. Lack of trusted networks for reporting or contribution the most sensitive issue in fair manners and due to less reliance on what traditional media portray in daily business of dissemination of audio video contents, the literate society has started believing on what new media presents in various forms. Equipped with the power of abundant sources of news and information ((via broadband, G3, G4 and web3) about any country or region the new media is rapidly making its footing worldwide. Mainstream media are the most important source, but not the only one. With the development of communication technologies, people now have access to a huge amount of information that was unthinkable 20 years ago. People can watch live proceeding of parliament, or read a transcript of it within hours. One can see press releases from newsmakers published on hundreds of websites, providing submission and distribution services on internet. New-style electronic formats, such as Internet discussion groups and chat rooms, create new public spaces and provide unprecedented opportunities for cultural and political discourse. Ecology of news and the style of passing on information have been changed dramatically. Geographical separation is not a big problem due to network linkage. Using FTP format you can transfer files anywhere in the word it was not possible for main stream media 2 decades ago. Second important characteristics its digital platform which has  enormous space to store audio, video, and Text. In new media environment distance makes little difference in the time, cost or speed of getting information. : Society has changed into families. People can get lot more quality and creditable information using news aggregators. In fact less gated social media have changed the ecology of News, thinking, behaviour and socio-economic environment Social media technologies take on many different forms including magazines, Internet forums, weblogs, social blogs, micro blogging, wikis, social networks, podcasts, photographs or pictures, video, rating and social bookmarking. The wall of fortress journalism is demolishing but Pakistan print and electronic mainstream media is not ready to adopt the new changes being taken place every passing day in communication technologies. People of Pakistan are swiftly moving toward social media aggregators than ever. This new tool provides reader/ viewers to obtain all required news and analysis on one simple point. The reason for this shift is that mainstream media is violating by keeping the important news with them and deliberately hiding facts from public eyes. Sensationalism in news and to be first in breaking news is considered as pride without knowing its impact on nation al security and integrity. Pakistani media regulators and broadcasters perhaps not aware what the west is doing through media. They must watch reports of PRESS TV.COM AND RT.COM. The West is swiftly and successfully achieving its targets one by one by to destabilize the situation in Syria, recently in Gaza. Author and investigative journalist Webster Tarpley has pointed in an interview at Russian Television (RT.COM) first English language TV that US Intelligence has announced the partition of Pakistan. Another report revealed in foreign media that US Special Forces have conducted secret raids inside Pakistan’s border regions. The operations were conducted between 2003 and 2008, but only one was ever made public. The mainstream media of Pakistan kept quite on these issues. In many cases Taliban refused to take responsibility for some explosions in public places in Pakistan than who is behind these brutal acts. Our investigative reporters are not well equipped to search the truth and report. Our media is highlighting issue base politic and projecting their allocated parties. Critical issues of society which should be the prime priority at present stage are not being suitably covered by any media outlet. Strong reaction in recent past has been seen in UK and USA where  people registered their protest and strongly criticize the biased, planned and narrow coverage of world affairs by the established media giants like Fox News, the BBC and NBS. Media regulators are seems to be helpless and may be part of this wrongdoing. Situation in Pakistan is changing rapidly and people have lost trust on the directed coverage of Pakistan’s media. Pakistan electronic media are being run by the print media journalists with no experience of working in electronic media and producing substandard and distorted facts. Broadcasters are making billions in profits while using the public airwaves. In return, they are not producing programmes that fulfill community needs. Because of above cited problems and the attitude of media groups of Pakistan people have started march against mainstream media using social media as a viable, quick and authentic source. This shift seems to be picking up the pace in near future. ***

Hamlet Siloquies

Hamlet gives us seven soliloquies, all centered on the most important existential themes: the emptiness of existence, suicide, death, suffering, action, a fear of death which puts off the most momentous decisions, the fear of the beyond, the degradation of the flesh, the triumph of vice over virtue, the pride and hypocrisy of human beings, and the difficulty of acting under the weight of a thought ‘which makes cowards of us all'.He offers us also, in the last act, some remarks made in conversation with Horatio in the cemetery which it is suitable to place in the same context as the soliloquies because the themes of life and death in general and his attitude when confronted by his own death have been with him constantly. Hamlet's soliloquy's reveal much about his character. However, they mainly seem to reveal that he is virtuous, though quite indecisive. These characteristics are explored through his various ways of insulting himself for not acting on his beliefs, and his consta nt need to reassure himself that his deeds are correct.Four of his seven soliloquies deserve our special attention: ‘O that this too sullied flesh would melt', ‘O what a rogue and peasant slave am I! ‘, ‘To be, or not to be, that is the question', and ‘How all occasions do inform against me'. In Act 1 Scene 2, Hamlet is suicidally depressed by his father’s death and mother’s remarriage. He is disillusioned with life, love and women. Whether ‘sullied’ or ‘solid’ flesh, the reference is to man’s fallen state.This is the fault of woman, because of Eve’s sin, and because the misogynistic medieval church had decreed that the father supplied the spirit and the mother the physical element of their offspring. Both words apply equally well, linking with the theme of corruption or the imagery of heaviness, but ‘solid’ is more subtle and fits better with the sustained metaphor of ‘meltingâ₠¬â„¢, ‘dew’ and ‘moist’, and the overarching framework of the four hierarchical elemental levels in the play: fire, air, water and earth. Melancholy was associated with a congealing of the blood, which also supports the ‘solid’ reading.In all likelihood it is a deliberate pun on both words by the dramatist and Hamlet. Other imagery concerns a barren earth, weed-infested and gone to seed, making the soliloquy an elegy for a world and father lost. Hamlet condemns his mother for lack of delay, and is concerned about her having fallen ‘to incestuous sheets’. His attitude to his dead father, his mother and his new father are all made clear to the audience here, but we may suspect that he has a habit of exaggeration and strong passion, confirmed by his use of three names of mythological characters.His reference to the sixth commandment — thou shalt not kill — and application of it to suicide as well as murder introduces the first of many Christian precepts in the play and shows Hamlet to be concerned about his spiritual state and the afterlife. Many of the play’s images and themes are introduced here, in some cases with their paired opposites: Hyperion versus satyr; heart versus tongue; heaven versus earth; ‘things rank and gross in nature’; memory; reason. In Act 1 Scene 5, having heard the Ghost’s testimony, Hamlet becomes distressed and impassioned.He is horrified by the behavior of Claudius and Gertrude and is convinced he must avenge his father’s murder. This speech is duplicative, contains much tautology, and is fragmented and confused. To reveal his state of shock he uses rhetorical questions, short phrases, dashes and exclamations, and jumps from subject to subject. God is invoked three times. The dichotomy between head and heart is mentioned again. In Act 2 Scene 2, Hamlet’s mood shifts from self-loathing to a determination to subdue passion and follow reason, applying this to the testing of the Ghost and his uncle with the play.The first part of the speech mirrors the style of the First Player describing Pyrrhus, with its short phrasing, incomplete lines, melodramatic diction and irregular metre. This is a highly rhetorical speech up to line 585, full of lists, insults and repetitions of vocabulary, especially the word ‘villain’; this suggests he is channelling his rage and unpacking his heart with words in this long soliloquy, railing impotently against himself as well as Claudius.He then settles into the gentler and more regular rhythm of thought rather than emotion. The irony being conveyed is that cues for passion do not necessarily produce it in reality in the same way that they do in fiction, and that paradoxically, deep and traumatic feeling can take the form of an apparent lack of, or even inappropriate, manifestation. Act 3 Scene 1 was originally the third soliloquy and came before the entry of the Players. Some directors therefore place this most famous of soliloquies at II. 2. 71, but this has the effect of making Hamlet appear to be meditating on what he has just been reading rather than on life in general whereas the Act III scene 1 placing puts the speech at the centre of the play, where Hamlet has suffered further betrayals and has more reason to entertain suicidal thoughts. The speech uses the general ‘we’ and ‘us’, and makes no reference to Hamlet’s personal situation or dilemma. Although traditionally played as a soliloquy, technically it is not, as Ophelia appears to be overtly present (and in some productions Hamlet addresses the speech directly to her) and Claudius and Polonius are within earshot.At the time this was a standard ‘question’ (this being a term used in academic disputation, the way the word ‘motion’ is now used in debating): whether it is better to liveunhappily or not at all. As always, Hamlet moves f rom the particular to the general, and he asks why humans put up with their burdens and pains when they have a means of escape with a ‘bare bodkin’. Hamlet also questions whether it is better to act or not to act, to be a passive stoic like Horatio or to meet events head on, even if by taking up arms this will lead to one’s own death, since they are not to be overcome.There is disagreement by critics (see Rossiter, p. 175) as to whether to ‘take up arms against a sea of troubles’ ends one’s opponent or oneself, but it would seem to mean the latter in the context. Although humans can choose whether to die or not, they have no control over ‘what dreams may come’, and this thought deters him from embracing death at this stage. Although death is ‘devoutly to be wished’ because of its promise of peace, it is to be feared because of its mystery, and reason will always counsel us to stick with what we know.Strangely, the Gho st does not seem to count in Hamlet’s mind as a ‘traveller’ who ‘returns’. Given that Hamlet has already concluded that he cannot commit suicide because ‘the Everlasting had†¦ fixed/His canon ’gainst self-slaughter’, there is no reason to think he has changed his mind about such a fundamental moral and philosophical imperative. C. S. Lewis claims that Hamlet does not suffer from a fear of dying, but from a fear of being dead, of the unknown and unknowable.However, Hamlet later comes to see that this is a false dichotomy, since one can collude with fate rather than try futilely to resist it, and then have nothing to fear. The ‘conscience’ which makes us all cowards probably means conscience in the modern sense, as it does in ‘catch the conscience of the King’. However, its other meaning of ‘thought’ is equally appropriate, and the double meaning encapsulates the human condition: to be cap able of reason means inevitably to recognize one’s guilt, and both thought and guilt make us fear punishment in the next life.With the exception of Claudius, intermittently and not overridingly, and Gertrude after being schooled by Hamlet, no other character in the play shows evidence of having a conscience in the sense of being able to judge oneself and be self-critical. This has a slower pace than the previous soliloquies, a higher frequency of adjectives, metaphors, rhythmical repetitions, and regular iambics. Hamlet’s melancholy and doubt show through in the use of hendiadys, the stress on disease, burdens, pain and weapons, and the generally jaundiced world view.The ‘rub’ referred to in line 65 is an allusion to an obstacle in a game of bowls which deflects the bowl from its intended path, and is yet another indirection metaphor. Act 3 Scene 2, Hamlet feels ready to proceed against the guilty Claudius. He is using the stereotypical avenger language an d tone in what the Arden edition calls ‘the traditional night-piece apt to prelude a deed of blood’. He is aping the previous speaker’s mode as so often, trying to motivate himself to become a stage villain, by identifying with Lucianus, the nephew to the king.This is the least convincing of his soliloquies because of the crudity of the cliched utterance, and one suspects it is a leftover from an earlier version of the revenge play. The emphasis at the end, however, is on avoiding violence and showing concern for his own and his mother’s souls; his great fear is of being ‘unnatural’, behaving as a monster like Claudius. He is, however, impressionable to theatrical performance, as we saw from his reaction to the Pyrrhus/Hecuba speeches earlier, and this carries him through to the slaying of Polonius before it wears off and, if we can believe it, ‘’A weeps for what is done’.This soliloquy creates tension for the audience, who are unsure of how his first private meeting with his mother will turn out and how they will speak to each other. He mentions his ‘heart’ and ‘soul’ again. Act 3 Scene 3, Hamlet decides not to kill Claudius while he is praying, claiming that this would send him to heaven, which would not be a fitting punishment for a man who killed his father unprepared for death and sent him to purgatory. For Hamlet revenge must involve justice.It begins with a hypothetical ‘might’, as if he has already decided to take no action, confirmed by the single categorical word ‘No’ in line 87, the most decisive utterance in the play. The usual diction is present: ‘heaven’, ‘hell’, ‘black’, ‘villain’, ‘sickly’, ‘soul’, ‘heavy’, ‘thought’, ‘act’. Act 4 Scene 4, Hamlet questions why he has delayed, and the nature of man and honor. He resolves again to do the bloody deed. Once again, he is not really alone; he has told Rosencrantz and Guildenstern to move away but they are still on stage, following their orders to watch him.Despite exhortation and exclamation at the end, this speech excites Hamlet’s blood for no longer than the previous soliloquies. Though it seems to deprecate passive forbearance and endorse the nobility of action — by definition one cannot be great if one merely refrains — the negative diction of ‘puffed’, ‘eggshell’, ‘straw’, ‘fantasy’ and ‘trick’ work against the meaning so that it seems ridiculous of Fortinbras to be losing so much to gain so little, and neither Hamlet nor the audience can be persuaded of the alleged honour to be gained.Fortinbras — who is not really a ‘delicate and tender prince’ but a ruthless and militaristic one, leader of a ‘list of lawless resolutes‘ — s eems positively irresponsible in his willingness to sacrifice 20,000 men for a tiny patch of ground and a personal reputation. Critics dispute whether Hamlet is condemning himself and admiring Fortinbras, having accepted that the way to achieve greatness is to fight and win, like his father, or whether he has now realized how ridiculous the quest for honor is, and that one should wait for it to come rather than seek it out.As the Arden editors point out, there is double-think going on, whereby ‘Hamlet insists on admiring Fortinbras while at the same time acknowledging the absurdity of his actions’ (p. 371). As so often when Hamlet is debating with himself and playing his own devil’s advocate, the opposite meaning seems to defeat the conscious argument he is trying to present. Lines 53 to 56 are grammatically obscure and add to the confusion. What is clear is Hamlet’s frustration with himself at the beginning of the soliloquy, which the 26 monosyllables com prising lines 43–46 powerfully convey.

Moral philosophy

In the film entitled ‘Liar Liar’ scripted by Paul Guay and Stephen Mazur, there several charaters who feature. These include such people as Fletcher Reede’s acting as Jimmy Carey, Justin cooper acting as Max, Maura Tierney as Reed’s estranged wife, and Jenniffer Tilly among others (www.totalfilm.com ). The movie is about smooth-talking attorney and habitual liar, manipulating his way to the helm of his job a local law company through winning great challenging cases. In the course of the film we find his son celebrating his fifth birthday. The son is seen at one time trying to encourage his father to lies.  Ã‚   This is because it is portrayed that this main character has lived and earned his career through lies. It is not clear whether that he will be able to win a case involving a character by the name Samantha Cole whose cases is on infidelity. The main character is also faced with the challenge of stopping his ex-wife taking his son to live with her in Boston. Through the application of lies Carrey survives in his career without the web of lies on which his career depends. In the movie Liar Liar, though clouded in comic laughter, there are several incidences whereby some acts are portrayed as immoral. The main character in this film in his endeavors to push his career up, he did some things which proved to be immoral. He pursued his cases based on a web of lies which worked wonders for. Though to him this was a success the acts were in themselves immoral. Based on Kant’s moral philosophy which states that an action is immoral not by virtue of its consequences but by the actual intentions of the actions. Kant further argued that moral requirements are based on a standard of rationality which he describes as â€Å"Categorical Imperative† (CI). In this case immorality will entail a violation of the categorical imperative and is therefore not rational (http://www.uchile.cl/bioetica/doc/honesty.htm). To be straight to the point, it is clear that we are commanded to exercise our wills in a particular manner and not to do some actions or others. It is therefore categorical in the course of applying to us unreservedly, or merely because we possesses rational wills. This is true because without indication to any ends that we might or might not have (http://www.uchile.cl/bioetica/doc/honesty.htm). Like his predecessors, Kant argues that moral requirements are based on standards of rationality which are either desire-based instrumental principles of rationality or based on pother rational intuitions. According to the film the main character acts against his duty of being honest to his clients and the public. This is against his duty to which he is called to. According to Kant, this is the only moral motive. In order to act morally people should to what is right guided by a sense of duty (www.answerbag.co.uk/q_view/398707). To conclude the movie gives us a picture of how people behave during their day to day life. During such times they go about doing things which to them are perceived as moral yet in actual sense do not constitute morality. The philosopher in this case i.e. Kant gives the true picture of what is moral and not moral. Works cited Truth and true professional, available at:   http://www.uchile.cl/bioetica/doc/honesty.htm, assessed on April 6, 2008 Kant: the moral order, available at: http://www.uchile.cl/bioetica/doc/honesty.htm, assessed on April 6, 2008 What is the basis of your moral philosophy?, available at: www.answerbag.co.uk/q_view/398707 – 65k – assessed on April 6, 2008 Liar Liar – film review, available at: www.totalfilm.com, assessed on April 6, 2008 Moral Philosophy I think that moral philosophy of Jeremy Bentham is the best suited for business and decision-making. Bentham’s philosophy is based on three principles of the greatest happiness, universal egoism and artificial identification of one’s interests. His philosophy is also referred to as utilitarianism. For example, Bentham argues: â€Å"By the principle of utility is meant that principle which approves or disapproves of every action whatsoever, according to the tendency which it appears to have to augment or diminish the happiness of the party whose interest is in question: or, what is the same thing in other words, to promote or to oppose that happiness†. I think that in our tough and often hostile business environment it is better to be universal egoism because in such a way you remain strong and steadfast defending your positions at the market place. The principle of greatest happiness can be interpreted in the way that company’s success makes leadership happy. Actually, Bentham philosophy is rational and logical, therefore, it is the best suited for our rational world. Bentham emphasizes the usefulness of things and actions meaning that everything should have its own place and purpose because it will lead to general happiness. Bentham approach is naturalistic as he promotes universal hedonism. He assumes that the primary motivators are pleasure and pain. The same is in business – when pain is felt, leadership and team do their best to cure the pain. Bentham also argues that humans are always seeking for the greatest happiness because their interests are interrelated with interests of other humans. Bentham’s moral philosophy held the advantage as the principle of utility is very popular. Compared to other principles, the principle of utility is very velar and enables decisions to be made where there is a need to solve the conflict of legitimate interests. Bentham’s philosophy is a fundamental commitment to human equality. Bentham’s principle of utility suggests that â€Å"one man is worth just the same as another man†. References Jeremy Bentham. The Internet Encyclopedia of Philosophy. Retrieved November 19, 2007, from http://www.utm.edu/research/iep/b/bentham.htm#H4                      Moral Philosophy In my opinion, David Hume’s moral philosophy is the best suited for business and decision-making process because it proclaims the principles justice, charity, benevolence, and patience. Moreover, Hume argues that ethics should play important role in decision-making process as it gives thinkers an opportunity to make such a decision won’t oppose anybody’s suggestions or preferences. He says that moral agent is motivated by character traits which nature is either virtuous or vicious. If a person is willing to donate money or things for charity, his actions are motivated by virtuous traits. In business decision-making, he notes, such traits should be natural and instinctive, and only in such person will make really ethical decisions. Hume’s moral philosophy is distinct and exact. (Fieser 2006) For example, Hume clearly divides qualities into virtuous and vice. The natural virtues are meekness, generosity, charity and benevolence, whereas artificial or vice virtues are chastity, greediness, dishonesty, and keeping promises. It seems that Hume places qualities needed for a well-ordered states as artificial. I think that in such a way he wants to show that business and decision-making should natural and instinctive. Agents are provided with psychological roles, though in certain situation a person may refer to more than entrusted role. (Fieser 2006) David Hume concludes that there are four categories of qualities necessary for moral business running and decision-making: 1.  Ã‚  Ã‚  Ã‚  Ã‚   Qualities useful for others: charity, fidelity, meekness, and benevolence; 2.  Ã‚  Ã‚  Ã‚  Ã‚   Qualities useful for oneself: patience and perseverance; 3.  Ã‚  Ã‚  Ã‚  Ã‚   Qualities agreeable to others: cleanliness, eloquence, and wit; 4.  Ã‚  Ã‚  Ã‚  Ã‚   Qualities agreeable to oneself: pride, humor, and self-esteem. Actually, David Hume discusses all the qualities which are considered the core of adequate business running. It is necessary to mention that to make really ethical decision means to use trained sensitivity to ethical issues. (Fieser 2006) References Fieser, Jame. (2006). Hume’s Moral Theory. Retrieved November 14, 2007, from http://www.iep.utm.edu/h/humemora.htm               

HUM112 Essay Example | Topics and Well Written Essays - 250 words

HUM112 - Essay Example What he is basically doing here is to avoid prior philosophical prejudices and embark on his journey with something fresh. It is the accumulation of his thought process that he summarizes the direction he takes as ‘I am thinking, therefore I exist’. He cannot doubt this knowledge which makes it easy for him to vouch for this fact. So the direction of his thoughts is built on ‘clear and distinct perception’; headed in a direction towards things that are purely impossible to doubt. This is when I was sure that the ending would be very different from the way that the reading had begun. And I was correct in the way the surprise ending was Descartes ends up confirming that God formulates the truth of apparent and distinct perceptions. 2) Since you were expecting a different ending, evaluate how successful the author was in convincing you to accept the validity of the â€Å"surprise ending† that was not clearly suggested at the beginning. Well while I appre ciate the interesting conclusion that the reading takes there are certain points that lead me to think that the evidence and argument that Descartes has put up to validate God are neither original nor very satisfying.