Static vs. Dynamic XML queries Essay Example | Topics and Well Written Essays - 250 words - 1

Static vs. Dynamic XML queries - Essay Example It enables data transfer from virtual or real documents in the wide world web to or from databases providing an interaction that is much needed. A static XML query is concerned with the retrieval of information and updating the node contents. It does not involve any other changes to the structure of the document (OLTEANU 2004). A dynamic XML query not only retrieves information and updates the content of the document in question; it also inserts new nodes while at the same time deleting the existing nodes often resulting in a change in the document structure. There has been a surge in the need for XML updates thanks to the growing preference for XML as a data exchange format. A labeling scheme supporting solely static XML queries is not enough for XML to become a general standard for data representation and exchange; a labeling scheme that effectively supports dynamic XML trees is also necessary (BEHRENDS 2007). However, dynamic queries are problematic and difficult to handle because they are require the updating of the labels of many nodes simultaneously with the updating of the original XML document to preserve the efficiency of the labeling scheme. GROPPE, J. (2008). Speeding up XML querying satisfiability test & containment test of XPath queries in the presence of XML schema definitions. LuÃÅ'ˆbeck, University, Diss.,

Existentialism in Demian and Crime and Punishment Essay Example for Free

Existentialism in Demian and Crime and Punishment Essay Existentialism is fairly common in literature, despite being a relatively new school of thought, and both Demian and Crime and Punishment show existentialist traits. This gives each book not just a philosophy, but also a certain feeling and mindset. Existentialism starts that with the idea that existence precedes essence, or purpose. We come into this world without a purpose, and we simply exist. Our task is to find a purpose. The world around us is an alien chaos, a circus that we stumble through, trying to find a meaning for our life. In Demian, it is clear that Sinclair does not know his purpose. His struggle is to find out what it is. Jean-Paul Sartre says, Life has no meaning a priori? its up to you to give it a meaning. Hesse declares that [e]ach man had only one genuine vocation? to find the way to himself?. His task was to discover his own destiny (Hesse, 132). It is clear, then, that we come into the world with nothing, no purpose at all. The only genuine task we have is to figure out what we are going to do here. According to Existentialism, no one can find it for you, and, similarly, no doctrine or philosophy can find it for you. Sinclair learns these same lessons. Demian pulls Sinclair away from mainstream religion early in the story, saying that the division of good and evil has no real meaning. Later, Pistorius tries to teach Sinclair about myriad past religions, but Sinclair rejects him, feeling that he should try to come up with something original instead. Throughout the story, Sinclair engages in different mentor-pupil relationships (like his relationships with Demian and Pistorius) but eventually he shrugs those off, taking his friends wisdom with him and facing the world alone. That is what everyone must do, eventually? face the world alone. And alone is exactly how we feel, as we stumble through this circus of a world. Sinclair spends most of his time not just feeling but also being by himself, adrift. When he leaves his family and his sisters, it does not affect him much, if at all, he is so isolated. He connects only with a precious few people, and never for very long. He somehow distances himself from his peers. Even when he was partying and drinking a lot, he found a way to separate himself from them. In that case, it was the role of sex in his life. Demian is a story about one mans journey. The reader never really learns the story of any other character, not even Demian himself, who remains something of an enigma to the very end. This puts the story in an existentialist mindset. Sinclair is drifting through a swirling, gray mass of humanity. Alone is also how we must act. Jean-Paul Sartre says, It is only in our decisions that we are important, and, We must act out passions before we can feel it. This pretty closely mirrors the sentiment presented when Pistorius says, [Y]ou cant consider prohibited anything that the soul desires (Hesse, 116). It is only when we make our own decisions and act for ourselves that what we do has meaning. Hesse puts the existentialist framework to work for him by using it to highlight the need for independence and spiritual self-reliance. Dostoyevsky, on the other hand, uses the mindset to facilitate Raskolnikovs downward mental spiral, highlight his aloofness, and pull the story along. The world of St. Petersburg is, without a doubt, a strange and hostile place for Raskolnikov. He stumbles along and things constantly happen around him. He repeatedly wakes up with people in his room. He sees things in the street, such as the drunken rape victim early in the story, or a prone Marmeladov, that cause him to lose his cool. More and more, he finds himself doing crazy things without regard for logic or even common sense. People in this world confound him. He has no idea what they are up to, and he is constantly paranoid that people are plotting against him. His guilty, delirious inner world combines with the crazy, chaotic outer world to make Raskolnikov into a raging, feverish, maniac. He is not just any raging, feverish, maniac, though. He is an aloof raging, feverish, maniac. He considers himself better than those around him, and his superior mentality drives his antisocial behavior. His antisocial behavior, in turn, gives the character and story a feeling of being alone. Not only is the world crazy, but also Raskolnikov is separated from it and everyone in it, at least until the very end of the book. He is isolated, so much so that at times he can feel it clearly with every fiber of his being that he could never again address these people (Dostoyevsky, 122). Finally, Dostoyevsky uses this chaotic world to drive his story along. Things are constantly happening by coincidence, and Dostoyevsky moves the plot forwards at a dizzying pace, forcing Raskolnikov to act. It is fantastic that Raskolnikov should happen upon Marmeladov soon after he is injured, and that Raskolnikov should overhear people discussing the very same murder that is on his mind, and that someone should eavesdrop on him and hear his confession. The frenzied plot makes it much easier for both Raskolnikov and the reader to slip into a mania, which is surely Dostoyevskys aim. The philosophy of existentialism, too, plays a part in Crime and Punishment. Sartre says that the only true goal of our lives is that which we set for ourselves. Raskolnikov, through the main portion of the story, has no clear goal. He wavers between wanting to turn himself in and trying to avoid suspicion. Sartre says, Man can will nothing unless he has first understood that [he has] no other aim than the one he sets himself, and it is clear that Raskolnikovs will is pretty much useless. He can effect no real change in either himself or in his surroundings until he finally picks a goal and follows through with it. His personal development is completely halted during his entire spell of indecision. Only in the epilogue do we see him begin to change, begin to forsake his philosophy of the superman, find happiness, and fall in love. The philosophy of existentialism was around long before anyone gave a name to it, as is evidenced by Dostoyevskys St. Petersburg, the perfect example of an existentialist world. Both Dostoyevsky and Hesse use existentialist ideas help them express their points. Andrew Holbrook, 2006.

Integration of WLANS, PAN, LAN and GSM in Hmanets

Integration of WLANS, PAN, LAN and GSM in Hmanets INTERWORKING ISSUES IN INTEGRATION OF WLANS, PAN, LAN AND GSM IN HMANETS KEY TO SYMBOLS OR ABBREVIATIONS AP Access Points AMASS Architecture for Mobile Ad-hoc Systems and Services AODV Ad Hoc on Demand Distance Vector Routing BS Base Station BNEP Bluetooth Network Encapsulation Protocol CDMA Code-Division Multiple Access CGSR Cluster-head Gateway Switch Routing CSMA/CA Carrier Sense Multiple Access with Collision Avoidance CTS Clear to Send DBTMA Dual Tone Multiple Access DSDV Destination Sequenced Distance Vector Routing DSR Dynamic Source Routing GEO-TORA Geographical Temporally Ordered Routing Algorithm GPRS General Packet Radio Service GPS Global Positioning System GRDL Grid Resource Description Language GSM Global System for Mobile Communication HF High Frequency HMANET Heterogeneous Mobile Ad Hoc Network HOLSR Hierarchical Optimized Link State Routing IP Internet Protocol LBR Location Based Routing LLC Logical Link Control MAC Medium Access Control MACA Multi Hop Collision Avoidance MACAW Medium Access Protocol for Wireless LAN MAN Metropolitan Area Network MANET Mobile Ad Hoc Network MPR Multipoint Relays NAT Network Address Translation NFS Network File System OLSR Optimized Link State Routing OSI Open Systems Interconnection PDA Personal Digital Assistant QoS Quality of Service RREP Route Reply RREQ Route Request RERR Route Error SCTP Stream Control Transmission Protocol SDR Software-Defined Radio TBRPF Topology Broadcast Based on Reverse Path Forwarding TC Topology Control TCP Transmission Control Protocol TDMA Time Division Multiple Access TORA Temporally Ordered Routing Algorithm VHF Very High Frequency WAN Wide Area Network WLAN Wireless Local Area Networks WPAN Wireless Personal Area Network WSDL Web Services Description Language WSN Wireless Sensor Network ZRP Zone Routing Protocol Chapter 1 1 INTRODUCTION Recent developments in wireless communications have taken possible applications from simple voice services in early cellular networks to newer integrated data applications. IEEE 802.11 family i.e. Wireless Local Area Networks (WLANs) have become popular for allowing low cost data transmissions [1]. The most common and approachable places, such as airports, hotels, shopping places, university campuses and homes have been provided with WLAN Access Points (AP) which provide hotspot connectivity . The future advances in modern radios like Software-Defined Radio (SDR) and cognitive radio technologies will surely facilitate the need of multi-mode, multi-interface and multi-band communication devices. This heterogeneous networking paradigm will certainly enable a user to enjoy better service quality, ease of use and mobility, while keeping in view the application needs and types of available access networks e.g. cellular network, WLAN, wireless personal area network (WPAN) etc. 1.1 Mobile Ad hoc Networks The Mobile Ad hoc Network (MANET) is a network formed by mobile wireless hosts without (necessarily) using a pre-existing infrastructure and the routes between these hosts may potentially contain multiple communication hops [2]. The autonomous nature of participating mobile nodes enables MANETs to have dynamic and frequently changing network topology. The nodes are self-organizing and behave as routers. The ease and speed of deployment and decreased dependence on infrastructure have made ad hoc networks popular within very short span of time. MANET variations include Personal area networking (e.g. cell phone, laptop, ear phone), Military environments (e.g. soldiers, tanks, aircraft), Civilian environments (e.g. cab network, meeting rooms, sports stadiums), and foremost Emergency operations (e.g. search-and-rescue, policing and fire fighting). MANETs rapid deployment, ease of use and subsequent properties make them a hot choice for many important applications. 1.1.1 Resource Sharing One of the intended aspects of MANETs is that it will facilitate the sharing of resources. These include both technical and information resources. Technical resources like bandwidth, Quality of Service (QoS), computational power, storage capacity and information resources include any kind of data from databases. Resource sharing among mobile devices require the devices to agree on communication protocols without the existence of any dedicated servers. 1.1.2 Coordination System Mechanisms that enable the sharing of resources between different mobile devices, i.e. different coordination system is necessary for sharing dissimilar resources. Examples of such mechanisms are Samba, Network File System (NFS) for sharing disk space and the distributed dot net client for sharing processor cycles. 1.1.3 Trust Establishment Before nodes start sharing any resource, they demand a certain amount of trust between them or systems with which they share resources. The level of trust depends on the kind of information or resources that is to be shared. For instance, sharing processor cycles require less trust than the sharing of personal information. Similarly, sharing of profit-making or highly sensitive information can require another level of trust establishment. There are systems currently in operation that can provide a certain amount of trust like the public key infrastructure that makes use of certificates. 1.1.4 Node Discovery Before any node starts communicating with other node, that node must be discovered. When a node enters the network, it has to be capable of communicating to the other nodes about its capabilities e.g. it is a Personal Digital Assistant (PDA) and it has a camera, Global Positioning System (GPS) capabilities and Global System for Mobile Communication (GSM) capabilities etc. When a node is detected, other users can send a query to the new device to find out what it has to offer. Commercial service providers can advertise the resources they have to offer through Internet Protocol (IP) multicasts. There is a myriad of standards that include resource description protocols like Standards Grid Resource Description Language (GRDL), the Web Services Description Language (WSDL) for telling all offer devices a way to describe and publish their specific resources and needs. There are also various different systems currently available that can gather these resource descriptions and structure them for other devices to use. 1.1.5 Resource description For any device to be able to use any resource, a way to identify and describe the resource has to be agreed upon by all available devices. If, for instance, storage capacity is to be shared, it first has to be clear what the capacity of each device is, and, what the storage need is. Although there are techniques to describe certain resources but not one technique that is able to provide this service for all resources. The available techniques combined, however, cover most of what is needed. 1.2 MANET Classifications Mobile Ad hoc Networks are usually categorized as Homogeneous MANETs and Heterogeneous MANETs. 1.2.1 Homogeneous MANETs When MANETs operate in fully Symmetric Environment whereby all nodes posses identical capabilities in terms of battery, processing powers, responsibilities and hardware and software capabilities, thus having no diversity, the network is Homogenous MANET. 1.2.2 Heterogeneous MANETs In certain environments, mobile nodes may have asymmetric capabilities in terms of transmission ranges, Medium Access Control (MAC), battery life, processing powers, speed of movement and software variations etc. Mobility rate may also differ in ad hoc networks due to varying traffic characteristics, transmission ranges, reliability requirements and communication needs. Similarly, addressing and traffic flows like host-based addressing, content-based addressing or capability-based addressing patterns may be defined in certain scenarios; for example, people sitting at an airport lounge, metro taxi cabs, sportsmen playing and military movements etc Homogenous MANETs do not allow for the heterogeneity in the network, which is seriously required in many scenarios, for instance, in a military battlefield network, where soldiers usually carry light portable wireless devices and more powerful equipment like High Frequency (HF) or Very High Frequency (VHF) is installed on vehicles. So, heterogeneous mobile nodes may co-exist in a single ad hoc network making it a Heterogeneous MANET. 1.3 Criterion for Heterogeneous MANETs The integration of different communication networks like cellular networks, WLANs, and MANETs is not straightforward due to various communication scenarios, different interface capabilities and dynamic mobility patterns of mobile nodes. This exhibits many possible application scenarios where devices may unexpectedly interact, create and receive random data streams (video and music etc), or request different network services. The drawback is that each network type typically uses its own protocol stack especially in the case of medium access. In fact, frequency allocation becomes more complicated since different wireless technologies like IEEE 802.11 a and IEEE 802.15.4 may possibly operate in the same frequency band, which makes coexistence mechanisms increasingly important. A heterogeneous MANET paradigm needs to be capable of providing subsequent characteristics. 1.3.1 Transparency The network should be capable of providing seamless end-to-end communication among mobile nodes i.e. the MANET user must not be informed about the route followed or network interfaces traversed by a communication session [3]. 1.3.2 Mobility Integration among dissimilar communication networks must facilitate mobile nodes via some mobility management framework that can manage flow of information through different medium access techniques [4]. 1.3.3 Addressing Most of the IP based networks consider each communication interface as an independent network device running under its own protocol stack [5]. However, this mechanism makes it difficult to remember destinations by IP addresses. So, there must be some mechanism similar to domain name service to recognize mobile nodes with more logical and easy to remember names. 1.3.4 Configuration Various configuration options like network ID, willingness for cooperative communications, desired mobility level and intended services shall be provided to mobile users for their convenience [6]. 1.3.5 End to End security Integration between various networks and data transfer over multiple wireless hops can even expose data to malicious nodes. Security mechanisms must take care of end-to-end data security as well as route security [7]. 1.3.6 Transmission Power and interference of Nodes MANET routing protocols must take care of issues arising due to various communication ranges like communication gray zones [4] and issues arising because of various communication technologies like Bluetooth and WLAN working in same frequency band [1]. 1.3.7 Utilization of Resources In heterogeneous networking paradigm, there may arise situations where some or most of the mobile nodes are installed with different kind of resources. For example, there may be some nodes installed with location monitoring devices like GPS. Now it is the responsibility of routing protocol to benefit from such capabilities in order to facilitate location aided routing and similar services [8]. 1.4 Problem Statement Current research efforts in mobile ad hoc networks are mainly converging towards inclusion of dissimilar communication technologies like IEEE 802.11 [9] and IEEE 802.15.4 [10] to a single mobile ad hoc network. Integrations of different networks like Wide Area Networks WANs (1G, 2G, 2.5G, 3G) and Metropolitan Area Networks MANs (IEEE 802.16) wherein users can access the system through a fixed base station (BS) or AP connected to a wired infrastructure in single hop fashion are also extending towards multihop communication environment using the new and revolutionary paradigm of a mobile ad hoc networks (MANETs), in which nodes constituting MANET serve as routers. Comprehensive research efforts have been done to address the issues related to infrastructure-less multihop communications among nodes installed with dissimilar communication capabilities [3, 11, 12, 13]. However, an investigation needs to be made in order to analyze and address the issues arising from such integrations. Such problems relate to both end users convenience (For example, remembering each destination with its IP address is a cumbersome job specially when every destination may carry multiple IP addresses and any communication interface may optionally be connected or disconnected) as well as networks performance; for example, routing to the best possible interface when there are multiple interfaces installed at destination. Likewise, optimized neighborhood sensing and position based routing can help to improve heterogeneous ad hoc networks performance and scalability. 1.5 Objectives The objective of this thesis is to study the integration of different technologies like WPAN, WLAN and GSM having different capabilities and protocol stacks to mobile ad hoc networks. Performance improvement issues relating to network configuration, human understandable naming mechanism and sophisticated location aided routing mechanisms will also be discussed and evaluated on an actual ad hoc network testbed. 1.6 Thesis Organization Chapter 2 describes the different design and technological challenges arising from integration of multiple communication interfaces. Chapter 3 includes an overview of famous heterogeneous routing protocols architectures, interworking issues encountered, the limitation and solution suggested. Chapter 4 specifically discusses the adopted solution. Chapter 5 presents the details about solution implementation, protocol evaluation testbed, proposed test cases for evaluation of the proposed mechanisms and results obtained, whereas; chapter 6 concludes the research work. Chapter 2 2 LITERATURE REVIEW 2.1 Introduction The literature available on heterogeneous MANETs has suggested different combination of access technologies but no comprehensive solution comprising of maximum access technologies has been suggested yet. Some of the suggested techniques will be discussed in succeeding paragraphs. 2.2 Service Architecture for Heterogeneous IP Networks It was presented by Joe C. Chan and Doan B. [14]. This proposal is presented to resolve two main issues i.e. universal connectivity and MANET location management in heterogeneous networks. The new architecture suggested for Mobile Ad-hoc Systems and Services (AMASS) introduces a new abstraction layer called Mobile P2P overlay in order to cater for the problems such as transparency, dynamic routing, unique addressing, association, and application independence. Mobile users can associate local resources from neighboring devices, build wireless on-demand systems which is independent of location, hardware devices, networking technology and infrastructure availability. Five key design considerations considered were Mobile Peer-to-Peer Overlay, Internet Interworking, Intelligent Overlay Routing, Infrastructure-free Positioning and Application Layer Mobility. Three enhanced mobility models offered in this approach are Personal Mobility (using different IP devices while keeping the same addr ess), Session Mobility (keeping the same session while changing IP devices) and Service Mobility (keeping personal services while moving between networks). The architecture is built on a peer-to-peer communication model to integrate MANETs seamlessly into heterogeneous IP networks. Mobile Peer-to-Peer System(P2P) is a distributed Middleware addresses the demand of direct communication needs by creating spontaneous community. Whenever the Mobile P2P system has global connectivity, it works with its peer system and other applications systems by generic P2P signaling. It consists of Ad-hoc Network layer and Mobile P2P Overlay. The former layer includes wireless hardware and MANET routing software offering homogeneous connectivity among nodes with same wireless interfaces. These nodes act as a router forwarding traffic toward its destination. The later layer includes the following core services: (i) Membership Services offers single sign-on, naming, profile and identity features; (ii) Discovery Services for peer/resource discovery and caching; (iii) Communication Services for Internet interworking, intelligent routing, session control, pres ence and service delivery; (iv) Location Services for infrastructure-free positioning, and user mobility management functions; (v) Adaptation Services for application and network services adaptation. Members of the Mobile P2P system should first sign-in a â€Å"common group† with their exclusive name and password. Some stationary nodes may also join to offer its resources such as Internet connection, printer, video conferencing. Whenever these client devices are within range of each other, they would work together as a team leading to a wireless adhoc service community where local resources could be shared by individual at its will. These members will then be available by intimating their capabilities and location information to the central location server. Information regarding physical location is also essential to offer spatial locality relationships and enable mobile content customization. The results which were achieved through this process can be summarized as first, it maximizes the synergies of MANETs and P2P for building wireless on-demand systems and services. MANETs provide dynamic physical connectivity while P2P offers dynamic associations of entities (users, devices, and services) for direct resources sharing. Second, its Mobile P2P overlay unites mobility, user-centric connectivity, and services for universal communications. This allow dynamic service adaptations pertinent to user location, application requirements, and network environments. Third, it presents a flexible network structure stimulating fixed and wireless networks convergence. The result is an â€Å"Integrated Mobile Internet† which makes our future environment lot better. 2.3 Transparent Heterogeneous Mobile Ad hoc Networks The idea was suggested by Patrick Stuedi and Gustavo Alonso[3]. The paper discussed that performance issues in a personal area network (PAN) or wireless sensor network (WSN) may have less priority than an office network. In contrast, battery life and low cost is vital to PANs and WSN while most probably it is not an issue in an office network. Consider a scenario where in a certain university campus the students carry variety of personal devices like mobile phones, PDA or laptops equipped with different communication technologies tailored to their capabilities. The mobile phones or PDA will be using Bluetooth whereas laptops have 802.11 as well as a Bluetooth interface built in technology. Ubiquitously combining all these devices into one mobile ad hoc network could invite new applications and services such as location based services or VoIP. So there may be an occasion where a personal device of one particular PAN might communicate with a personal device of another PAN in a multi-ho p fashion with the underlying MAC scheme changing per hop. In this scenario two issues needs to be solved i.e. broadcast emulation and handover. Broadcast emulation is not directly supported in Bluetooth (nor on nodes comprising both Bluetooth and 802.11). Handover is an issue because, in the case of heterogeneous MANETs, a handover might include a change in how the medium is accessed. A handover can be caused by node mobility, a change in user preferences (where due to energy constraints the user chooses to use Bluetooth instead of 802.11), or performance reasons. [15] Any device or node supporting multi interface though having different protocol stack will be specific to the interface at lower level. This characteristic will deteriorate the ability of a device to switch from one network to the other. The objective of such network is to provide an end-to-end communication abstraction that hides heterogeneity. The different possible design differs from each other with regard to application transparency, performance and mobility. There is another issue of handover which includes route changes as well as MAC switching. In principle, there are three possible scenarios 2.3.1 Horizontal Handover The horizontal handover between the participating nodes take place when the route changes and underlying MAC technology remains the same. 2.3.2 Vertical Handover The route does not change but the given neighbor is now reached through a new physical interface. 2.3.3 Diagonal Handover The diagonal handover takes when the MAC technology and route between the participating nodes change simultaneously. To address all these issues an IP based heterogeneous mobile ad hoc test bed using Bluetooth and IEEE 802.11 that implements a virtual interface approach as the end-to-end abstraction is presented. 2.4 Stream Control Transmission Protocol Another approach presented by R. Stewart, Q. Xie, and K. Morneault is [16] Stream Control Transmission Protocol, a transport protocol defined by the IETF providing similar services to TCP. It ensures reliable, in-sequence delivery of messages. While TCP is byte-oriented, SCTP deals with framed messages. A major involvement of SCTP is its multi-homing support. One (or both) endpoints of a connection can consist of more than one IP addresses, enabling transparent fail-over between hosts or network cards. Each interface could be separately cond and maintained (AODV-UU [17] e.g., supports multiple interfaces). This solution seems to be quite valuable in terms of performance since SCTP optimizes the transmission over multiple links. In fact, if one particular node can be reached through several interfaces, SCTP switches transmission from one interface to another after a predefined number of missing acknowledgements. Unfortunately, the solution lacks transparency. Applications running traditional unix sockets would have to be changed to use SCTP sockets instead. Another problem arises with the connection oriented nature of Bluetooth. In Bluetooth, interfaces appear and disappear dynamically depending on whether the connection to the specific node is currently up or down. Therefore, this is something that both the ad hoc routing protocol as well as SCTP would have to cope with. 2.5 Global connectivity for IPv6 Mobile Ad Hoc Networks R. Wakikawa, J. T. Malinen, C. E. Perkins, A. Nilsson, and A. J. Tuominen, in 2003 through IETF Internet Draft, 2003 presented Global connectivity for IPv6 Mobile Ad Hoc Networks, suggested one of the solutions for connecting heterogeneous MANETs. Before this work, the issue was solved by the traditional Internet model. But by adopting the approach presented by them the non structured MANETs were made to operate in structured environment, and inevitably limit the extent of flexibility and freedom that an evolving Mobile Internet can offer. Current mobile positioning and network mobility solutions are mainly infrastructure-driven which is contradictory to infrastructure-less MANETs. Without a flexible and user-centric network structure, existing solutions are generally insufficient to handle the dynamic and on-demand requirements of MANETs. 2.6 Conclusion Heterogeneous MANET service architectures and routing protocols have been talked about and it is established that lots of enhancements need to be introduced to the heterogeneous ad hoc networks. First of all, different issues like IP addresses to hostname mapping and seamless communication need to be addressed. Secondly, ad hoc networks must seamlessly utilize all underlying interfaces. Finally, research efforts need to converge towards real-world network deployment as very few MANET service architectures have been evaluated on actual network testbeds. Chapter 3 3 INTEGRATION CHALLENGES 3.1 Introduction The invention of mobile devices like laptops, personal digital assistant (PDA), smart phones and other handheld gadgets having dissimilar communication interfaces smooth the progress of data transmissions without any predetermined infrastructure and centralized administration. [18]. Such data transmissions can only be made on top of infrastructure-less networks composed of fully autonomous mobile nodes. But, these infrastructure-less networks do possess many complexities like dynamic and ever changing topology, heterogeneity in nodes, energy constraints, bandwidth constraints, limited security and scalability. However, there user-friendliness and rapid deployment make them an imperative part of 4th Generation (4G) architecture allowing the mobile users to communicate anytime, anywhere and with the help of any device. 3.2 Technological Challenges The specialized nature of MANETs enforces many challenges for protocol design by incorporating changes in all layers of protocol stack [2]. For instance, all the changes in link characteristics must be dealt with physical layer. MAC Layer should ensure fair channel access and avoidance of packet collision. Calculation of best possible routes among mobile autonomous nodes must be done by the network layer. Transport layer must modify its flow control mechanism to tolerate Packet loss and transmission delays arising because of wireless channel. The continuous making or breaking of connection due to nodes mobility be handled by application layer. These issues at each layer need to be handled effectively in order to smooth the transition from traditional network to advanced MANETs. 3.2.1 The Physical Layer In heterogeneous MANETs there can be a node which may be able to access multiple networks simultaneously. If a node on one hand, is connected to a cellular network, and on the other hand it exists within the coverage area of an 802.11b AP, the network or the node should be able to switch between them. Moreover, in heterogeneous environment, different wireless technologies may operate in the same frequency band and it is significant that they coexist without degrading each others performance. Therefore, techniques to reduce interference between nodes are important. For example, a node communicating with other nodes via multihop path may have lesser interference than a node communicating directly with AP. This is due to the attachment of increased number of nodes to the AP. Another way of reducing interference is Power control techniques applied in code-division multiple access (CDMA)-based cellular networks and MANET [15]. The research issues range from designing considerations to power control techniques include efficient design of nodes that can efficiently switch between different technologies and ensure higher data rates, development of Interference attenuation techniques between various wireless access technologies, modulation techniques and coding schemes that improve the performance of a given technology and frequency planning schemes for increasing the utilization of frequency spectrum 3.2.2 Link Layer The data link layer can be divided into Logical Link Control (LLC) and Medium Access Control (MAC) layers. When a node needs to communicate to another node having cellular interface, it uses a centralized MAC access like Time Division Multiple Access (TDMA) or CDMA with a data rate upto 2.4 Mb/s. On the other hand, when a node communicates in 802.11 environments, it uses distributed random access scheme like Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) upto a data rate of 11 Mb/s. So, this difference of data rate is going to be one of the interworking considerations. Due to dissimilar access technologies at intermediate hops, the performance of ad hoc networks deteriorates. The problems such as hidden and exposed terminals also limit the capacity of MANETs. The need of evolving mechanisms such as power control and power aware MAC protocols is mandatory to improve the performance of ad hoc networks. In a heterogeneous network, the cross-layer design may play a significant role in providing useful information to upper layers. Another important issue to be considered at the link/MAC level is Security. Although, end-to-end security is the responsibility in the application layer, some wireless access technologies provide a certain level of security at the lower layers. Although the link and MAC layers in a multi-interface node can operate autonomously, but their operations have to be optimized to provide definite service to the upper layers. Some of the open issues include design of efficient link and MAC layer protocols to support QoS in Heterogonous MANET, channel administration schemes that consider different categories of traffic, and allow call blocking and handoff failure probabilities and security at Link / MAC layer. 3.2.3 Network Layer The network layer needs to integrate all underlying communication interfaces; therefore, it is the most challenging task. The presence of nodes with multiple communication interfaces allow to have different physical and MAC layer technologies which need to be taken into account while dealing with an integrated routing process. But, the problem of MANETs such as frequent route changes due to mobility, higher communication overhead to learn and uphold valid routes, higher end-to-end delay and limited end-to-end capacity due to problems at the lower layers are main contributing factors in designing of routing process [19]. In order to reduce network control traffic, improve throughput and increase the range, the idea of integrating MANETs with infrastructure networks is evolved. Hence, mechanism to find gateways and correctly con IP addresses is required by such nodes in a MANET. The network layer has to find the best route between any source and destination pair. To define the best route, including number of hops, delay, throughput, signal strength, and so on several metrics can be used. Moreover, the network layer has to handle horizontal handoffs between the same technology and vertical handoffs between different technologies in a seamless manner. Several routing protocols have been presented for heterogeneous MANETs but the design of integrated and intelligent routing protocols is largely open for research with issues like development of routing capability in a heterogeneous environment that supports all communication possibilities between nodes forming MANET, scalability in multihop routing withou t significantly escalating the overhead and study of the impact of additional routing constraints (like co-channel interference, load balance, bandwidth), and requirements (services, speed, packet delay) needed by nodes and networks. 3.2.4 Transport Layer In connection oriented transport session, as in case of Transmission Control Protocol (TCP), packet loss is assumed to occur due to congestion in the network. This assumptions leads to the performance degradation of TCP and factors such as channel errors, jitter and handoffs are overlooked. Moreover, in heterogeneous environments, the transport protocol has to handle the high delays involved in vertical hands off (while switching from one interface to another), server migration, and bandwidth aggregation [16]. Sometimes, a node changes its IP address when it needs

Evaluating the Impact of Tourism in England Essay -- UK, Britain

Tourist Count During our visit to Ashridge Estate, we carried a tourist count on two honey pot locations known as Bridgewater Monument and Ivinghoe Beacon. 1 out of the 4 groups that visited Ashridge carried out the tourist count as we did not want to hassle the tourists. A member from the group stood at an area in both locations and took a count of the amount of teenagers, adults, OAP’s, family groups and children there were. The information was then tallied onto a table. From this, we will compare the results collected to previous years (2004-2005). The comparison will be useful as it will allow us to analyse the information to see whether there is a correlation between the number of tourism and the hypothesis. If the number of tourists has decreased, then good; less damage done to the wildlife and environment. However, if the number of tourists increased, it may also suggest that the negative impacts have likewise increased. Some of the negative impacts may be footpath erosion; more tourists use the footpath resulting in more damage, Littering; animals may eat the litter which could harm them and also the air/noise pollution created via tourist transportation; affects the air quality and environment of the local wildlife. As we took the tourist count, we categorized the tourists into age groups. The reason for this was to see which age group was more likely to have a negative impact in Ashridge. Children and teenagers for example tend to be more energetic in comparison to OAP’s, doing more active activities that could harm the local wildlife and environment e.g. football; sports. Whilst OAP’s are more passive and less energetic doing activities that are less likely to harm the wildlife and environment e.g. bird watching. So... ...to see whether they were affected by tourism. On the sketch we took detailed annotations to help us visualize the problems we saw such as footpath erosion, debris materials scattered, deep rutted soil and other negative impacts. From this we could see the difference in both footpaths ((un)managed) to see which one was more affected by tourism. The problem with the field sketches was that whilst we were drawing, it was really windy which subsequently distracted us, so there may have been some mistakes. Also, some of the pupils from the groups found it difficult to draw what they saw, so the sketches may also not have been accurate and reliable. We could improve our drawings by taking a camera to capture accurate photos that will give us reliable results. From the pictures we would be able to recall the features of the footpaths we saw in order to help our fieldwork.

Project Scope and Charter Essay

The first phase of any project is the initiation phase. This phase commences when some type of business issue or opportunity is identified bringing about a proposal project to solve or address the issue or opportunity. The main deliverable of this phase is the project charter, which contains a broad view of what the project is about, who is involved, why the project is being conducted and how & when the project will be carried out. (Hughes Lecture, 2013) Once the charter is approved the project can move into the planning phase, which is where the charter is used to identify the scope of the project. This paper will examine the relationship between project scope and charter and highlight the benefits of each. Project Charter The project charter is a short document that serves as an informal contract between the project team and the sponsor of the project. (Kloppenberg, 2012, pg 84) This document contains only enough detail to get the project approved so it can move into the planning phase. Project Management Professional, Ritchie Hughes describes the charter as a representation of the â€Å"view from 3000 meters†. The project charter is usually drawn up by the Project Manager and team, or, in instances where a Project Manager has not yet been assigned, the project sponsor will complete the charter. Hughes explains that the functions of the â€Å"why† section of the charter are to ensure: the correct individuals will be consulted (e.g. stakeholders and governance), projects that are linked or dependent on the project in question are identified, the organization has enough resources (internally or externally) to complete the project, a business case for the organization is conveyed and that all the information is provided to support the executive team. (Hughes Lecture, 2013) Approval of the charter grants authority to the project manager to go through with the project and utilize the allotted budget or resources for the project activity. As the charter approval is the â€Å"Go/No Go† decision for the project, a non-approval means termination of the project. (Hughes Lecture, 2013) Scope Approval of the project charter signifies the transition into the planning phase of the project. A critical part of the planning phase is identifying the scope of the project. Project scope is defined as â€Å"the work that must be performed to deliver a product, service, or result with the specified features and functions.† (Kloppenberg, 2012, pg. 142) Ritchie Hughes explained that scope can also mean â€Å"the sum of products, services and results to be provided as a project.† The benefits of scope are that the work to be performed is clarified, listed and any work not to be completed (outside the project’s scope) is identified. Scope is also a useful tool in managing expectations and avoiding assumptions among stakeholders and the project team. (Hughes Lecture, 2013) Scope Creep A common issue when managing a project’s scope is dealing with scope creep. Scope creep can be defined as â€Å"the extra deliverables that can creep into a project.† (Collegiate Projects, 2013, pg. 1) These â€Å"project improvements† can be very hard to avoid but may have a major effect on the project’s budget, timing or quality. Projects that may be susceptible to scope creep should have a scope change management plan that contains: a definition of scope change for the project, a process for submitting and reviewing scope changes, documentation needed for the change process and a tool to track change requests and their resolutions. (Collegiate Projects, 2013, pg. 2,3) An understanding by both parties (project team and sponsor) of scope creep and its effects on the project, and an organized management plan will help avoid scope creep that may negatively affect the project’s success. Conclusion In the early stages of project management, two very important aspects are the project charter and scope of the project. Not all projects need a charter but understanding and managing the scope of a project will help the project team effectively complete the project in time and budget without â€Å"Gold Plating†. References Kloppenborg, T. J. (2012). Contemporary project management: organize, plan, perform (2nd ed.). Mason, Ohio: South-Western Cengage Learning. (2013). Managing Scope Creep. Collegiate Project Services, 1, 1-3. Hughes, R. (Director) (2013, January 31). Project Initiation: Scope & Charters. Bus 427. Lecture conducted from Tom Rippon, Victoria.

Description of the Diskobolos

Description of the Diskobolos When sculpted in 450 B.C.E., the Diskobolos was originally crafted in bronze. The sculptor, Myron, used a technique called hollow-casting which was common for Greek sculptors of the Archaic period. The title of the sculpture, Diskobolos, means "disk thrower" in Greek. This sculpture has been reproduced thousands of times, including many marble copies made by the Romans, and plaster casts like the one in our library.The Diskobolos is a very detailed sculpture. The musculature of it shows the athletic ability of Greek athletes. The athlete is sculpted in the nude like many of the other Greek sculptures. The sculpture is attempting to capture the art of athletic ability, during strenuous tasks. The athlete is in the climax of his action. Yet in the action, the athlete is concentrating on his task. The lack of expression on his face and the glare of the eyes portray his concentration.Map of "The archaic period in Greece (750 BC – 4...He is leaning forward at the hip. His upper bod y is twisted showing the torque needed to propel the discus. The athlete's legs are bent at the knees. With all the action going on in his body, the athlete still maintains his center of gravity which is necessary for him to complete the throw. The muscles over the entire sculpture are well defined. His shoulders are clearly defined from the rest of his arms. His chest has well defined pectoral muscles as well as abdominal muscles.Athletic ability was very important to the Greek's. For the first time in history we have art portraying athletes in action. Today the entire world still celebrates the Greek Olympic Games. The gamers were created more than 2500 years ago by the Greeks. Today the winners of the games receive medals, but in ancient Greece the athletes received crowns of olives. The athletes were...