Crime And The Impact On Modern Society

Crime And The Impact On Modern Society The threat and fear of crime are constant concerns that impact many people in modern society. The safety of schools and communities are usually indicated by crime rates, and are justifiably major factors in choosing where to reside. Research denotes that juveniles are involved in numerous crimes each year, as perpetrators who are subjected to legal intervention for status offenses such as running away, school truancy and curfew violations and as victims (Regoli, Hewitt, Delisi, 2007). Literature review reveals that there are official measures of juvenile crime which include those by police, the courts, and corrections agencies; and unofficial measures of juvenile crime such as self-report and victim surveys, that try to give a more complete description of the true extent of juvenile crime (Schmalleger, Bartollas, 2008). This paper will discuss several methodologies of official and unofficial measurements of juvenile delinquency and the identifiable problems with these types of data collections. Keywords: Uniform Crime Report, National Incident-Based Reporting System, self-reporting Criminologists for years have recognized that there are major problems in defining and measuring juvenile delinquency. The first is the legal definition that applies to youth who have been officially labeled in juvenile court. Legal definitions vary by time and place, making comparisons difficult because they are not uniform in all jurisdictions with respect to age of the prosecution; thus they tend to provide an unrealistic picture of the extent and nature of delinquency since they deal only with youth who are caught and processed (Regoli et al., 2007). Behavioral definitions in contrast to the legal definition can sometimes provide a more accurate picture of the extent and nature of delinquency and the characteristics of the offenders and victims. By using behavioral definitions, juveniles who violate statutes are seen as delinquent whether or not they are officially labeled (Regoli et al., 2007). The results have the appearance of delinquency being evenly distributed across social class and more frequent than official statistics would lead us to believe; thus showing a highly noted problem of relying on self-reporting processes and the difficulties in collecting accurate data (Regoli et al., 2007; Schmalleger, 2009). Measurement is not new to the juvenile justice system. Too often data collected by juvenile justice agencies have been unrelated to outcomes, and seldom allowed the public to assess performance in a meaningful way (Schmalleger, Bartollas, 2008). I suggest that this one of the reasons information does not completely help juvenile justice systems and organizations determine impact or cost-effectiveness of their interventions. Data is most useful when it provides input to juvenile justice professionals regarding public awareness and support, and can provide citizens and other government stakeholders with a sense of what the juvenile justice systems and agencies are really accomplishing or trying to accomplish. Official Measuring of Juvenile Delinquency Even with all the debates about the methodology of juvenile delinquency measurement, official crime statistics are considered the most accurate measures of crime and are often used in the news media and by justice agencies. This data is usually compiled by police, courts, and corrections agencies. The Uniform Crime Report (UCR) a program which began in 1929 and provides this type of data on the national and local levels, and track occurrences of eight specific crimes including the locations and frequencies of each (Lynch, Jarvis, 2008). This useful information is collected by the Federal Bureau of Investigation (FBI) from law enforcement agencies across the country, and presents descriptive statistical, historical profile of violent juvenile crime in America based on the percentage of all arrests (Lynch, Jarvis, 2008). Another official measure for data collection of juvenile crime is the National Incident-Based Reporting System (NIBRS). This system was developed in 1988 by the federal government to address some of the shortcomings of the UCR, and is generated from the records management systems of federal, state and local agencies (Regoli, et al., 2007). The NIBRS which collects information on every arrest and incident was intended to be a broader crime reporting system in comparison to the UCR program; and it gives much greater details on specific crimes because it differentiates between crimes that are attempted and crimes that are completed (Schmalleger, 2009). Proponents for official measurements have recently argued that these measures show validity for certain crimes; any problems tend to be stable over time allowing trends and patterns to surface; there is easy to access to the data and relatively inexpensive; they allow for city and regional trend comparisons; and they provides detailed information on reporting patterns, who is arrested, and homicides (Lynch, Jarvis, 2008). In contrast, opponents have raised the issues that the reports do not capture unreported crime because under or over reporting by law enforcement often referred to as the dark figure of crime; and as it relates to juvenile crimes the number of arrests is not equal to the actual number of youths who committed crime, and group arrests overestimate juvenile crime (Lynch, Jarvis, 2008). Un-Official Measuring of Juvenile Delinquency Even though most of the fundamental problems with official crime statistics had been identified before the end of the nineteenth century, including the major problem of the dark figure of unknown crime, it was not until the mid-twentieth century that systematic attempts to unravel some of the mysteries of official statistics were initiated (Regoli, et al., 2007). Turning to data sources outside of the official agencies of criminal justice, unofficial crime statistics were generated in order to explore the dark figure of crime not known to the police, and to create measures of crime that were independent of the official registrars of crime and crime control, which many felt would address more validity and reliability issues in the measurement of crime (Doerner, Lab, 2005). One un-official data collecting measure used for juvenile delinquency is self-reporting. These reports are confidential questionnaires administered to samples of youth who voluntarily report on their own involvement in delinquent activities, which sometimes provide a more complete picture of juvenile delinquency (Webb, Katz, Decker, 2006). They however are not error free. These measures use population samples that arguably are small, and it has been suggested by some criminologists that they are not representative of juvenile offenders as a whole (Webb et al., 2006). Recently, it has been proposed by some researchers that victim surveys recognize the inadequacies of official measures of crime, particularly the apparently substantial volume of crime and victimization that remains unknown to, and therefore un-acted upon by, criminal justice authorities (Doerner, Lab, 2005). The National Crime Victimization Survey (NCVS), a survey sponsored by the federal government and has been collecting data on personal and household victimization since 1973 (Doerner, Lab, 2005). It was designed with four primary objectives: to develop detailed information about the victims and consequences of crime; to estimate the number and types of crimes not reported to the police; to provide uniform measures of selected types of crimes; and to permit comparisons over time and types of areas (Doerner, Lab, 2005). In general, victimization surveys have the same problems and threats to validity and reliability as any other social-science survey. Ironically, there is a double dark figure of hidden crime that is not reported to interviewers in victimization surveys designed to uncover crimes not reported to the police (Doerner, Lab, 2005). Such incomplete reporting of victimization means that victimization surveys, like official data sources, also underestimate the true amount of crime, and this then suggests that the discrepancy between the crime rate estimates of the victim surveys and the UCR may be even larger than reports indicate. A noted strength of victim surveys is that most crimes included in the questionnaire are F.B.I. index crimes; but research also reveals that two index crimes (murder and arson) are not included in the survey, though many other important crimes are measured in the victimization surveys (Doerner, Lab, 2005). It is fair to argue that many times the results from thi s type of data collection show that the victimization statistics are somewhat limited in their representativeness and generalizing ability. Conclusion Debates have been heated over the last few decades on the proper way to measure delinquency. Research reveals that there are three major sources of data that have been used, self-reports of delinquent behavior, victimization surveys, and official accounts (e.g., arrests, court records) (Regoli et al., 2007). These sources of data results do not always agree, and studies have shown that certain methodologies such as survey-reports show weaker associations between social status (e.g., poverty, race, gender) and delinquency than official records (Regoli et al., 2007). Proponents for methodological measurements argue that these sources of data yield reasonably similar patterns when the object of inquiry is serious and persistent delinquency (Schmalleger, 2009). I suggest there is still a need for more methodologies to aid in the challenges of prevention and recidivism juvenile crime.

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

Dress Code Implementation Into the NBA Essay -- Papers

Dress Code Implementation Into the NBA The controversial issue as of late is whether or not a dress code should be implemented into the NBA. These athletes are being paid millions of dollars a year and serve as role models to children all over the world. For these reasons it is essential that a dress code be implemented into the NBA. Last year during the Olympics, at one of Belgrade’s finest restaurants, Allen Iverson, Carmelo Anthony, LeBron James and many other U.S. players attended a dinner in their honor. The guest list included many respectable people including the Serbian national team, who were all wearing matching sport coats. Iverson and some of his fellow NBA professionals arrived wearing an array of sweat suits, oversize jeans, shimmering diamond earrings and platinum chains, according to NBA officials at the dinner. Larry Brown, the Hall of Fame coach of the U.S. team, was shocked and humiliated. He told an NBA official that he thought about sending some of the worst dressed players back to the hotel (Washington Post). The story of this incident eventually made its way back to the office of David Stern, the commissioner of the NBA. There was already a rising concern about how some of the players were dressing and how the overall appeal of the game was being destroyed. The NBA had tried to fuse its product with the hip hop culture, trying to connect with a new generation of fans and their street fashion. This plan of attack was very unsuccessful (Washington Post). Looking at the statistics, not only were they unsuccessful, ... ... from. Like I said before, the NBA is a business, and the main objective of a business is to make money. They have to realize that the big money in sports comes from corporate dollars: Sponsorships, Commercials, and Luxury Suites. The NBA can afford to risk alienating a few kids or slow sales of throwback jerseys, because portraying their players as professionals earns $350,000 more corporate dollars from another sold commercial spot. And this is the money that they want (Not Exactly Rocket Science). In conclusion, the players of the NBA have the abilities of a professional, are paid like professionals, and are powerful role models among the youth of society. With great power comes great responsibility, and these players must be men and own up to their responsibilities of dressing like professionals.

Struggles for Release Essay -- Comparative, Kate Chopin, Nathaniel Haw

The two American short stories, â€Å"The Story of an Hour† by Kate Chopin and â€Å"Young Goodman Brown† by Nathaniel Hawthorne both portrays a similar theme. The two protagonists in both short stories suffer mental or emotional torture and was trap in a literary cage. In addition, both characters in the stories meet death in the end, and that death symbolizes their freedom from the world and society that was grasping on to them. A main topic of American short stories that constantly shows up since the earlier years, and is presented throughout history is the emphasis on society and how it creates emotional and mental tortures in an individual, and imparts them with a different perspective of the world. The society that people live in has an enormous effect on them, and the way they live their lives. The protagonist in â€Å"The Story of an Hour† by Kate Chopin, Louise Mallard, suffers from the society she lives in because of its expectations of marriage. After her husband’s supposed death, ironically, Louise feels relief and joy, for she has found a way to escape society’s restraints, â€Å"A kind intention or a cruel intention made the act seem no less a crime as she looked upon it in that brief moment of illumination† (Chopin 316). The society in which Mrs. Mallard belongs to forces her to lose her freedom, a freedom she yearned for in the years she was trapped in the marriage. By being confined in a marriage and losing her freedom, Mrs. Mallard reacts in an untypical way when she’s notified of her husband’s supposed death. When Louise is told by her sister, Josephine, that her husband is gone, she cries for a second but ironically rejoices and looks forward to the years ahead and hopes that she will live a long life, â€Å"She breathed a quick ... ...in character who were trapped in the cage, finally gets released and escapes through death. Both Louise Mallard and Goodman Brown suffer from emotional or mental torture that is exerted by their society and their expectations. Also, both main characters in Chopin’s and Hawthorne’s writing was similar in that they both seek for a better life than what the society they live in offer them. Louise Mallard yearned for freedom when her society limits independence for women through the expectations of conjoining in marriage. At the same time, Goodman Brown seeks for a society where mankind has no evil wills and all are innocent, but society is inherently sinful since the time of Adam and Eve. The protagonists suffer in their time and era, but in the end they both free their souls from the clutch of society and liberate themselves from their emotional and mental tortures.

Artificial Contraception :: essays research papers fc

There are many forms of artificial contraception. I am going to discuss some of those forms and the Church’s opinion. Condoms, or rubbers, are shaped like a balloon and are made of a special kind of rubber. Condoms prevent sperm from reaching the cervix. They are placed over the male’s erect penis before intercourse. They are 80-90% effective. No prescription is needed to use them. They protect against STD’s. They are more protective in preventing AIDS, then preventing pregnancy. They are not fully effective because they can break, have defects, be slippery, or it can be too old. Spermicides such as: creams, foams, vaginal supporsitones, and vaginal film form a chemical barrier that kills or makes the sperm inactive, which makes it impossible to become pregnant. They are 80% effective. It is available without a prescription and provides some STD protection. Effectiveness is increased if used with condoms. Vasectomies are common for men. The tube that carries the sperm is cut and tied which prevents sperm from being ejaculated. It is 99% effective This procedure is permanent and is done through a small incision near the testicles. It does not affect sexual arousal. A cervical cap is a soft rubber dome that forms a barrier to prevent sperm from reaching the cervix. The spermicidal gel kills the sperm. It is 85% effective. It may give some protection against chlamydia and gonorrhea. The diaphragm does the same thing as a cervical cap and is 85% effective. It is a flat rubber-like disk which has to be fitted from a doctor. It is placed inside the woman’s vagina before having intercourse. It is often used with cream or jelly that is placed around the edge of the diaphragm. There is a very high failure rate because sometimes they are not fitted or inserted correctly. They create fewer health risks for women. It may reduce the risk of cervical cancer and provides some STD protection. There are also injections for men and women. In men, a dr ug is injected into the sperm duct to disable the sperm for a period of time. Depo-Provera injections that contain the hormone, progesterone is injected and it prevents the release of an egg from the ovary. It is 99% effective. It is long lasting and highly effective. It also protects against uterine cancer. But it does not protect against STD’s. Female condoms are 75-85% effective but 95% effective if used correctly.

Chapter 10 summary of Guns, Germs, and Steel Essay

In the Fertile Crescent, plants and animals spread quickly into Europe and North Africa. Innovations such as written language and wheels spread similarity quickly as well. People used domesticated crops rather than those that grew naturally. This shows that people easily adapted the Fertile Crescent’s food production. Chapter 10: Eurasia has covered the largest East to West area of any continent. Diamond believes that this is yet another r advantage for Eurasia. Eurasia had â€Å"amber fields of grain and spacious skies†. With the New world not having these advantages, it slowed diffusion. In the Fertile Crescent, plants and animals spread quickly into Europe and North Africa. Innovations such as written language and wheels spread similarity quickly as well. People used domesticated crops rather than those that grew naturally. This shows that people easily adapted the Fertile Crescent’s food production. Chapter 10: Eurasia has covered the largest East to West area of any continent. Diamond believes that this is yet another r advantage for Eurasia. Eurasia had â€Å"amber fields of grain and spacious skies†. With the New world not having these advantages, it slowed diffusion. In the Fertile Crescent, plants and animals spread quickly into Europe and North Africa. Innovations such as written language and wheels spread similarity quickly as well. People used domesticated crops rather than those that grew naturally. This shows that people easily adapted the Fertile Crescent’s food production. Chapter 10: Eurasia has covered the largest East to West area of any continent. Diamond believes that this is yet another r advantage for Eurasia. Eurasia had â€Å"amber fields of grain and spacious skies†. With the New world not having these advantages, it slowed diffusion. In the Fertile Crescent, plants and animals spread quickly into Europe and North Africa. Innovations such as written language and wheels spread similarity quickly as well. People used domesticated crops rather than those that grew naturally. This shows that people easily adapted the Fertile Crescent’s food production.

Ed Philosophy Essay

Philosophy of education can refer to either the academic field of applied philosophy or to one of any educational philosophies that promote a specific type or vision of education, and/or which examine the definition, goals and meaning of education. As an academic field, philosophy of education is â€Å"the philosophical study of education and its problems†¦ its central subject matter is education, and its methods are those of philosophy†. [1] â€Å"The philosophy of education may be either the philosophy of the process of education or the philosophy of the discipline of education. That is, it may be part of the discipline in the sense of being concerned with the aims, forms, methods, or results of the process of educating or being educated; or it may be metadisciplinary in the sense of being concerned with the concepts, aims, and methods of the discipline. â€Å"[2] As such, it is both part of the field of education and a field of applied philosophy, drawing from fields of metaphysics, epistemology, axiology and the philosophical approaches (speculative, prescriptive, and/or analytic) to address questions in and about pedagogy, education policy, and curriculum, as well as the process of learning, to name a few. [3] For example, it might study what constitutes upbringing and education, the values and norms revealed through upbringing and educational practices, the limits and legitimization of education as an academic discipline, and the relation between educational theory and practice. Instead of being taught in philosophy departments, philosophy of education is usually housed in departments or colleges of education, similar to how philosophy of law is generally taught in law schools. [1] The multiple ways of conceiving education coupled with the multiple fields and approaches of philosophy make philosophy of education not only a very diverse field but also one that is not easily defined. Although there is overlap, philosophy of education should not be conflated with educational theory, which is not defined specifically by the application of philosophy to questions in education. Philosophy of education also should not be confused with philosophy education, the practice of teaching and learning the subject of philosophy. Philosophy of education can also be understood not as an academic discipline but as a normative educational theory that unifies pedagogy, curriculum, learning theory, and the purpose of education and is grounded in specific metaphysical, epistemological, and axiological assumptions. These theories are also called educational philosophies. For example, a teacher might be said to follow a perennialist educational philosophy or to follow a perennialist philosophy of education. Contents * 1 Philosophy of Education * 1. 1 Idealism * 1. 1. 1 Plato * 1. 1. 2 Immanuel Kant * 1. 1. 3 Georg Wilhelm Friedrich Hegel * 1. 2 Realism * 1. 2. 1 Aristotle * 1. 2. 2 Avicenna * 1. 2. 3 Ibn Tufail * 1. 2. 4 John Locke * 1. 2. 5 Jean-Jacques Rousseau * 1. 2. 6 Mortimer Jerome Adler * 1. 2. 7 Harry S. Broudy * 1. 3 Scholasticism * 1. 3. 1 Thomas Aquinas * 1. 3. 2 John Milton * 1. 4 Pragmatism * 1. 4. 1 John Dewey * 1. 4. 2 William James * 1. 4. 3 William Heard Kilpatrick * 1. 4. 4 Nel Noddings * 1. 4. 5 Richard Rorty * 1. 5 Analytic Philosophy * 1. 5. 1 Richard Stanley Peters * 1. 5. 2 Paul H. Hirst * 1. 6 Existentialism * 1. 6. 1 Karl Jaspers * 1. 6. 2 Martin Buber * 1. 6. 3 Maxine Greene * 1. 7 Critical Theory * 1. 7. 1 Paulo Freire * 1. 8 Postmodernism * 1. 8. 1 Martin Heidegger * 1. 8. 2 Hans-Georg Gadamer * 1. 8. 3 Jean-Francois Lyotard * 1. 8. 4 Michel Foucault * 2 Normative Educational Philosophies * 2. 1 Perennialism * 2. 1. 1 Allan Bloom * 2. 2 Progressivism * 2. 2. 1 Jean Piaget * 2. 2. 2 Jerome Bruner * 2. 3 Essentialism * 2. 3. 1 William Chandler Bagley * 2. 4 Social Reconstructionism and Critical Pedagogy * 2. 4. 1 George Counts * 2. 4. 2 Maria Montessori * 2. 5 Waldorf * 2. 5. 1 Rudolf Steiner * 2. 6 Democratic Education * 2. 6. 1 A. S. Neill * 2. 7 Classical Education * 2. 7. 1 Charlotte Mason * 2. 8 Unschooling * 2. 8. 1 John Holt * 2. 8. 2 Contemplative education * 3 Professional organizations and associations * 4 References * 5 Further reading * 6 External links| Philosophy of Education Idealism Plato Inscribed herma of Plato. (Berlin, Altes Museum). Main article: Plato Date: 424/423 BC – 348/347 BC Plato’s educational philosophy was grounded in his vision of the ideal Republic, wherein the individual was best served by being subordinated to a just society. He advocated removing children from their mothers’ care and raising them as wards of the state, with great care being taken to differentiate children suitable to the various castes, the highest receiving the most education, so that they could act as guardians of the city and care for the less able. Education would be holistic, including facts, skills, physical discipline, and music and art, which he considered the highest form of endeavor. Plato believed that talent was distributed non-genetically and thus must be found in children born in any social class. He builds on this by insisting that those suitably gifted are to be trained by the state so that they may be qualified to assume the role of a ruling class. What this establishes is essentially a system of selective public education premised on the assumption that an educated minority of the population are, by virtue of their education (and inborn educability), sufficient for healthy governance. Plato’s writings contain some of the following ideas: Elementary education would be confined to the guardian class till the age of 18, followed by two years of compulsory military training and then by higher education for those who qualified. While elementary education made the soul responsive to the environment, higher education helped the soul to search for truth which illuminated it. Both boys and girls receive the same kind of education. Elementary education consisted of music and gymnastics, designed to train and blend gentle and fierce qualities in the individual and create a harmonious person. At the age of 20, a selection was made. The best one would take an advanced course in mathematics, geometry, astronomy and harmonics. The first course in the scheme of higher education would last for ten years. It would be for those who had a flair for science. At the age of 30 there would be another selection; those who qualified would study dialectics and metaphysics, logic and philosophy for the next five years. They would study the idea of good and first principles of being. After accepting junior positions in the army for 15 years, a man would have completed his theoretical and practical education by the age of 50. Immanuel Kant Main article: Immanuel Kant Date: 1724–1804 Immanuel Kant believed that education differs from training in that the latter involves thinking whereas the former does not. In addition to educating reason, of central importance to him was the development of character and teaching of moral maxims. Kant was a proponent of public education and of learning by doing. [4] Georg Wilhelm Friedrich Hegel Main article: Georg Wilhelm Friedrich Hegel Date: 1770–1831 Realism Aristotle Bust of Aristotle. Roman copy after a Greek bronze original by Lysippos from 330 B. C. Main article: Aristotle Date: 384 BC – 322 BC Only fragments of Aristotle’s treatise On Education are still in existence. We thus know of his philosophy of education primarily through brief passages in other works. Aristotle considered human nature, habit and reason to be equally important forces to be cultivated in education. [1] Thus, for example, he considered repetition to be a key tool to develop good habits. The teacher was to lead the student systematically; this differs, for example, from Socrates’ emphasis on questioning his listeners to bring out their own ideas (though the comparison is perhaps incongruous since Socrates was dealing with adults). Aristotle placed great emphasis on balancing the theoretical and practical aspects of subjects taught. Subjects he explicitly mentions as being important included reading, writing and mathematics; music; physical education; literature and history; and a wide range of sciences. He also mentioned the importance of play. One of education’s primary missions for Aristotle, perhaps its most important, was to produce good and virtuous citizens for the polis. All who have meditated on the art of governing mankind have been convinced that the fate of empires depends on the education of youth. [2] Avicenna Main article: Avicenna Date: 980 AD – 1037 AD In the medieval Islamic world, an elementary school was known as a maktab, which dates back to at least the 10th century. Like madrasahs (which referred to higher education), a maktab was often attached to a mosque. In the 11th century, Ibn Sina (known as Avicenna in the West), wrote a chapter dealing with the maktab entitled â€Å"The Role of the Teacher in the Training and Upbringing of Children†, as a guide to teachers working at maktab schools. He wrote that children can learn better if taught in classes instead of individual tuition from private tutors, and he gave a number of reasons for why this is the case, citing the value of competition and emulation among pupils as well as the usefulness of group discussions and debates. Ibn Sina described the curriculum of a maktab school in some detail, describing the curricula for two stages of education in a maktab school. [5] Ibn Sina wrote that children should be sent to a maktab school from the age of 6 and be taught primary education until they reach the age of 14. During which time, he wrote that they should be taught the Qur’an, Islamic metaphysics, language, literature, Islamic ethics, and manual skills (which could refer to a variety of practical skills). [5] Ibn Sina refers to the secondary education stage of maktab schooling as the period of specialization, when pupils should begin to acquire manual skills, regardless of their social status. He writes that children after the age of 14 should be given a choice to choose and specialize in subjects they have an interest in, whether it was reading, manual skills, literature, preaching, medicine, geometry, trade and commerce, craftsmanship, or any other subject or profession they would be interested in pursuing for a future career. He wrote that this was a transitional stage and that there needs to be flexibility regarding the age in which pupils graduate, as the student’s emotional development and chosen subjects need to be taken into account. [6] The empiricist theory of ‘tabula rasa’ was also developed by Ibn Sina. He argued that the â€Å"human intellect at birth is rather like a tabula rasa, a pure potentiality that is actualized through education and comes to know† and that knowledge is attained through â€Å"empirical familiarity with objects in this world from which one abstracts universal concepts† which is developed through a â€Å"syllogistic method of reasoning; observations lead to prepositional statements, which when compounded lead to further abstract concepts. † He further argued that the intellect itself â€Å"possesses levels of development from the material intellect (al-‘aql al-hayulani), that potentiality that can acquire knowledge to the active intellect (al-‘aql al-fa‘il), the state of the human intellect in conjunction with the perfect source of knowledge. â€Å"[7]