The ban on smoking in public places Essay Example | Topics and Well Written Essays - 1750 words

The ban on smoking in public places - Essay Example Even then researchers had concerns about the hazards of smoking as they pertained to second hand smoke and people who inhaled it(Comfort pp 14). Commonly referred to as passive smoke, those who were around smoke without actually smoking themselves soon proved to have several definitive health risks associated with being near the smoke and inhaling it through passive (second hand methods). â€Å"Medical concerns about the dangers of passive smoking--inhaling other peoples tobacco smoke--can be traced back to the 1920s, and there is also now a widespread consensus that such passive smoking can cause disease. Other peoples tobacco smoke, either from the burning tip of a cigarette or the smoke that is exhaled by the smoker, is classed as a known human carcinogen by the US Environmental Protection Agency(Comfort pp 14). â€Å" For the most part public place for the purpose of legislative ban incorporated any â€Å"enclosed or semi-enclosed area that members of the public have access to which provides a business or a service including workplaces, buildings and public transport(Comfort pp 14). â€Å" â€Å"Direct benefits revolve mainly about respiratory health, and regular exposure to smoke may trigger asthma in infants and young children. The indirect benefits to young peoples health associated with smoke-free policies is seen to relate to the general reinforcement of the messages that non-smoking is now increasingly the norm within the community and would thus help to promote non-smoking lifestyles in future adult generations(Comfort pp 14).†

Group Plan Essay Example | Topics and Well Written Essays - 3750 words

Group Plan - Essay Example 365). A more recent research conducted by Reynolds, Chen and Herbers (2009) indicates that mobility can not only impact students’ academic performance but can also increase the risk of dropping out. This study examined the consequences of student mobility for academic performance and dropout rates in 16 research studies conducted from 1990-2008. Result findings indicate that student mobility accounted for a 1/3 higher rate of both academic under achievement and drop-out rates (1). Rumberger (2002) advices that since nothing can be done about mobility the best response is to inform students and their families of the difficulties that are associated with â€Å"changing schools and how to mitigate them† (p.1). Specifically, Rumberger (2002) recommends that schools should be prepared in advance for the reception of highly mobile students in order to facilitate the transitioning process the moment they arrive. Moreover, schools should set up â€Å"ongoing activities and pro cedures to address the needs of the new student† (Rumberger 2002, p. 2). This group plan is therefore guided by Rumberger’s advice and the documented evidence of the propensity for academic underperformance of students in regular or frequent transition. ... It is difficult to predict the number of students that will be participating in each session, but it is expected to have at least five students and could be as much as twenty. At any rate, teacher representatives from each grade will be asked to participate in the group plan as a means of ensuring that incoming students and their parents/guardians can address any concerns about the curriculum and anything specific to their grade. These teachers are also expected to provide reassurance that they are there for the students and their parents/guardians and when and where they can be contacted. Academic dean, Arthur Baldridge will also be asked to participate in the sessions as frequently as possible. His role is merely to introduce himself and to make himself available to students and their parents/guardians. How Members will be selected Members will be selected by reference to the enrolment register. The enrolment register will inform of new and incoming students. Staff will be selected from among teachers and counsellors based on expertize and availability. The Academic Dean is very important because he administers and plans according to goals set for the student and the academic needs of the students. By participating in the group plan, the Academic Dean will focus special attention on the academic needs of transitioning students. Logistics: The sessions will be conducted once a week for one hour per session for six weeks. The sessions will be held in discussion form and since questionnaires will be distributed in the first and last sessions, it is best to hold the sessions in a classroom. Leadership Skills: As a leader of this

Food Inc Essay Example for Free

Food Inc Essay How is the text you have studied in class constructed to portray certain ideas? Documentaries are usually constructed to portray one point of view, whether it is a negative or positive point of view. Food Inc directed by Robert Kenner, presents a many ideas about how the fast food industry is affecting the ways in which Americans eat. They do this by showing one perspective instead of both. Food Inc doesn’t explore in to detail the positive aspects of fast food; they are just focusing on the negative. They construct the documentary using techniques such as expert opinions, Interviews and statistics to present certain ideas throughout the documentary. The main idea explored throughout the documentary was the animal cruelty caused by humans due to modifying the development of animals. They ways in which they present this ideas is mainly through footage of the animals suffering and the juxtaposition of the animals before they were modified and how the animals are now. The footage of the crowded cows helpless and unable to move creates a setting which portrays a negative feel and creatively making us feel sympathetic towards the animals. The shots of the chickens not being able to walk due to the genetic modifications of the animal, creates the idea of humans purposely provoking animal cruelty. They are changing the ways in which an animal develops for their own needs and generally to make more money. This is clearly shown through the juxtaposition of the â€Å"old† chicken and the â€Å"new† chicken. This Juxtaposition makes us question how it is possible to grow a chicken in half the time yet be double the size? It therefore makes the documentary more engaging as we are starting to question the farmers ourselves and therefore are dragged into believing what the documentary is trying to portray. Another idea explored in the documentary Food Inc is the constant conflict of the prices of healthy foods compared to the prices in fast food restaurants. The ways in which Robert Kenner has constructed the documentary to perceive the fast food outlets being cheaper is through an interview with the Gonzalez family. They are an average sized American family who eat fast food due to their financial status. Kenner used the juxtaposition of the price of a meal at McDonalds to buying a meal at the supermarkets. At McDonalds the Gonzalez family can buy a burger and drink each for 11$, they then show you the Gonzalez family inside a grocery store struggling to buy a lettuce for under 2$ which worked out to be the cost of their whole meal at McDonalds. This makes believe what Kenner is trying to portray and are drawn into believing that fast food is always cheaper than the groceries. However we are not given any cheap healthy displays in the supermarket, instead given with cheap unhealthy items such as 99 cent cokes. Kenner has purposely portrayed the unhealthy items in a negative way to create an opinion that we are being â€Å"forced† in to fast food rather than having the choice of fast food.

Implementation of New Computer Network

Implementation of New Computer Network Here we are going to implement an new computer network for this company that 25 employees have been working in. Suppose you want to build a computer network, one that has potential to grow to global proportions to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design t integrate these building blocks into an effective communication service? Suppose you want to build a computer network, one that has the potential togrow to global proportions and to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design to integrate these building blocks into an effective communication service? Answering this question is the overriding goal of — to describe the available building materials and then to show how they can be used to construct a network from the ground up. Before we can understand how to design a computer network, we should first agree on exactly what a computer network is. At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe computers. To some, the term implies the voice telephone network. To others, the only interesting network is the cable network used to disseminate video signals. The main thing these networks have in common is that they are specialized to handle one particular kind of data (keystrokes, voice, or video) and they typically connect to special-purpose devices (terminals, hand receivers, and television sets). What distinguishes a computer network from these other types of networks? Probably the most important characteristic of a computer network is its generality. Computer networks are built primarily from general-purpose programmable hardware, and they are not optimized for a particular application like making phone calls or delivering television signals. Instead, they are able to carry many different types of data, and they support a wide, and ever-growing, range of applications. This chapter looks at some typical applications of computer networks and discusses the requirements that a network designer who wishes to support such applications must be aware of. Once we understand the requirements, how do we proceed? Fortunately, we will not be building the first network. Others, most notably the community of researchers responsible for the Internet, have gone before us. We will use the wealth of experience generated from the Internet to guide our design. This experience is embodied in a network architecture that identifies the available hardware and software components and shows how they can be arranged to form a complete network system. To start us on the road toward understanding how to build a network, this chapter does four things. First, it explores the requirements that different applications and different communities of people (such as network users and network operators) place on the network. Second, it introduces the idea of a network architecture, which lays the foundation for the rest of the book. Third, it introduces some of the key elements in the implementation of computer networks. Finally, it identifies the key metrics that are used to evaluate the performance of computer networks. 1.1 APPLICATIONS Most people know the Internet through its applications: the World Wide Web, email, streaming audio and video, chat rooms, and music (file) sharing. The Web, for example, presents an intuitively simple interface. Users view pages full of textual and graphical objects, click on objects that they want to learn more about, and a corresponding new page appears. Most people are also aware that just under the covers, each selectable object on a page is bound to an identifier for the next page to be viewed. This identifier, called a Uniform Resource Locator (URL), is used to provide a way of identifying all the possible pages that can be viewed from your web browser. For example, http://www.cs.princeton.edu/~llp/index.html is the URL for a page providing information about one of this books authors: the string http indicates that the HyperText Transfer Protocol (HTTP) should be used to download the page, www.cs.princeton.edu is the name of the machine that serves the page, and /~llp/index.html uniquely identifies Larrys home page at this site. What most Web users are not aware of, however, is that by clicking on just one such URL, as many as 17 messages may be exchanged over the Internet, and this assumes the page itself is small enough to fit in a single message. This number includes up to six messages to translate the server name (www.cs.princeton.edu) into its Internet address (128.112.136.35), three messages to set up a Transmission Control Protocol (TCP) connection between your browser and this server, four messages for your browser to send the HTTP get request and the server to respond with the requested page (and for each side to acknowledge receipt of that message), and four messages to tear down the TCP connection. Of course, this does not include the millions of messages exchanged by Internet nodes throughout the day, just to let each other know that they exist and are ready to serve web pages, translate names to addresses, and forward messages toward their ultim ate destination. Another widespread application of the Internet is the delivery of streaming audio and video. While an entire video file could first be fetched from a remote machine and then played on the local machine, similar to the process of downloading and displaying a web page, this would entail waiting for the last second of the video file to be delivered before starting to look at it. Streaming video implies that the sender and the receiver are, respectively, the source and the sink for the video stream. That is, the source generates a video stream (perhaps using a video capture card), sends it across the Internet in messages, and the sink displays the stream as it arrives. There are a variety of different classes of video applications. One class of video application is video-on-demand, which reads a pre-existing movie from disk and transmits it over the network. Another kind of application is videoconferencing, which is in some ways the more challenging (and, for networking people, interesting) case because it has very tight timing constraints. Just as when using the telephone, the interactions among the participants must be timely. When a person at one end gestures, then that action must be displayed at the other end as quickly as possible. Too much delay makes the system unusable. Contrast this with video-on-demand where, if it takes several seconds from the time the user starts the video until the first image is displayed, the service is still deemed satisfactory. Also, interactive video usually implies that video is flowing in both directions, while a video-on-demand application is most likely sending video in only one direction. One pioneering example of a videoconferencing tool, developed in the early and mid-1990s, is vic. shows the control panel for a vic session. vic is actually one of a suite of conferencing tools designed at Lawrence Berkeley Laboratory and UC Berkeley. The others include a whiteboard application (wb) that allows users to send sketches and slides to each other, a visual audio tool called vat, and a session directory (sdr) that is used to create and advertise videoconferences. All these tools run on Unix—hence their lowercase names—and are freely available on the Internet. Many similar tools are available for other operating systems. It is interesting to note that while video over the Internet is still considered to be in its relative infancy at the time of this writing (2006), that the tools to support video over IP have existed for well over a decade. Although they are just two examples, downloading pages from the Web and participating in a videoconference demonstrate the diversity of applications that can be built on top of the Internet, and hint at the complexity of the Internets design. Starting from the beginning, and addressing one problem at time, the rest of this book explains how to build a network that supports such a wide range of applications. Chapter 9 concludes the book by revisiting these two specific applications, as well as several others that have become popular on todays Internet. 1.2 REQUIREMENTS We have just established an ambitious goal for ourselves: to understand how to build a computer network from the ground up. Our approach to accomplishing this goal will be to start from first principles, and then ask the kinds of questions we would naturally ask if building an actual network. At each step, we will use todays protocols to illustrate various design choices available to us, but we will not accept these existing artifacts as gospel. Instead, we will be asking (and answering) the question of why networks are designed the way they are. While it is tempting to settle for just understanding the way its done today, it is important to recognize the underlying concepts because networks are constantly changing as the technology evolves and new applications are invented. It is our experience that once you understand the fundamental ideas, any new protocol that you are confronted with will be relatively easy to digest. The first step is to identify the set of constraints and requirements that influence network design. Before getting started, however, it is important to understand that the expectations you have of a network depend on your perspective: An application programmer would list the services that his application needs, for example, a guarantee that each message the application sends will be delivered without error within a certain amount of time. A network designer would list the properties of a cost-effective design, for example, that network resources are efficiently utilized and fairly allocated to different users. A network provider would list the characteristics of a system that is easy to administer and manage, for example, in which faults can be easily isolated and whereitiseasytoaccountfor usage. This section attempts to distill these different perspectives into a high-level introduction to the major considerations that drive network design, and in doing so, identifies the challenges addressed throughout the rest of this book. 1.2.1 Connectivity Starting with the obvious, a network must provide connectivity among a set of computers. Sometimes it is enough to build a limited network that connects only a few select machines. In fact, for reasons of privacy and security, many private (corporate) networks have the explicit goal of limiting the set of machines that are connected. In contrast, other networks (of which the Internet is the prime example) are designed to grow in a way that allows them the potential to connect all the computers in the world. A system that is designed to support growth to an arbitrarily large size is said to scale. Using the Internet as a model, this book addresses the challenge of scalability. Links, Nodes, and Clouds Network connectivity occurs at many different levels. At the lowest level, a network can consist of two or more computers directly connected by some physical medium, such as a coaxial cable or an optical fiber. We call such a physical medium a link,and we often refer to the computers it connects as nodes. (Sometimes a node is a more specialized piece of hardware rather than a computer, but we overlook that distinction for the purposes of this discussion.) As illustrated in, physical links are sometimes limited to a pair of nodes (such a link is said to be point-to-point), while in other cases, more than two nodes may share a single physical link (such a link is said to be multiple-access). Whether a given link supports point-to-point or multiple-access connectivity depends on how the node is attached to the link. It is also the case that multiple-access links are often limited in size, in terms of both the geographical distance they can cover and the number of nodes they can connect. If computer networks were limited to situations in which all nodes are directly connected to each other over a common physical medium, then networks would either be very limited in the number of computers they could connect, or the number of wires coming out of the back of each node would quickly become both unmanageable and very expensive. Fortunately, connectivity between two nodes does not necessarily imply a direct physical connection between them—indirect connectivity may be achieved among a set of cooperating nodes. Consider the following two examples of how a collection of computers can be indirectly connected. shows a set of nodes, each of which is attached to one or more point- to-point links. Those nodes that are attached to at least two links run software that forwards data received on one link out on another. If organized in a systematic way, these forwarding nodes form a switched network. There are numerous types of switched networks, of which the two most common are circuit-switched and packet-switched. The former is most notably employed by the telephone system, while the latter is used for the overwhelming majority of computer networks and will be the focus of this book. The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other. Think of these blocks of data as corresponding to some piece of application data such as a file, a piece of email, or an image. We call each block of data either a packet or a message, and for now we use these terms interchangeably; we discuss the reason they are not always the same in Section 1.2.2. Packet-switched networks typically use a strategy called store-and-forward. As the name suggests, each node in a store-and-forward network first receives a complete packet over some link, stores the packet in its internal memory, and then forwards the complete packet to the next node. In contrast, a circuit-switched network first establishes a dedicated circuit across a sequence of links and then allows the source node to send a stream of bits across this circuit to a destination node. The major reason for using packet switching rather than circuit switching in a computer network is efficiency, discussed in the next subsection. The cloud in distinguishes between the nodes on the inside that implement the network (they are commonly called switches, and their primary function is to store and forward packets) and the nodes on the outside of the cloud that use the network (they are commonly called hosts, and they support users and run application programs). Also note that the cloud in is one of the most important icons of computer networking. In general, we use a cloud to denote any type of network, whether it is a single point-to-point link, a multiple-access link, or a switched network. Thus, whenever you see a cloud used in a figure, you can think of it as a placeholder for any of the networking technologies covered in this book. A second way in which a set of computers can be indirectly connected is shown in . In this situation, a set of independent networks (clouds) are interconnected to form an internetwork, or internet for short. We adopt the Internets convention of referring to a generic internetwork of networks as a lowercase i internet, and the currently operational TCP/IP Internet as the capital I Internet. A node that is connected to two or more networks is commonly called a router or gateway, and it plays much the same role as a switch—it forwards messages from one network to another. Note that an internet can itself be viewed as another kind of network, which means that an internet can be built from an interconnection of internets. Thus, we can recursively build arbitrarily large networks by interconnecting clouds to form larger clouds. Just because a set of hosts are directly or indirectly connected to each other does not mean that we have succeeded in providing host-to-host connectivity. The final requirement is that each node must be able to state which of the other nodes on the network it wants to communicate with. This is done by assigning an address to each node. An address is a byte string that identifies a node; that is, the network can use a nodes address to distinguish it from the other nodes connected to the network. When a source node wants the network to deliver a message to a certain destination node, it specifies the address of the destination node. If the sending and receiving nodes are not directly connected, then the switches and routers of the network use this address to decide how to forward the message toward the destination. The process of determining systematically how to forward messages toward the destination node based on its address is called routing. This brief introduction to addressing and routing has presumed that the source node wants to send a message to a single destination node (unicast). While this is the most common scenario, it is also possible that the source node might want to broadcast a message to all the nodes on the network. Or a source node might want to send a message to some subset of the other nodes, but not all of them, a situation called multicast. Thus, in addition to node-specific addresses, another requirement of a network is that it supports multicast and broadcast addresses. The main idea to take away from this discussion is that we can define a network recursively as consisting of two or more nodes connected by a physical link, or as two or more networks connected by a node. In other words, a network can be constructed from a nesting of networks, where at the bottom level, the network is implemented by some physical medium. One of the key challenges in providing network connectivity is to define an address for each node that is reachable on the network (including support for broadcast and multicast connectivity), and to be able to use this address to route messages toward the appropriate destination node(s). 1.2.2 Cost-Effective Resource Sharing As stated above, this book focuses on packet-switched networks. This section explains the key requirement of computer networks—efficiency—that leads us to packet switching as the strategy of choice. Given a collection of nodes indirectly connected by a nesting of networks, it is possible for any pair of hosts to send messages to each other across a sequence of links and nodes. Of course, we want to do more than support just one pair of communicating hosts—we want to provide all pairs of hosts with the ability to exchange messages. The question, then, is how do all the hosts that want to communicate share the network, especially if they want to use it at the same time? And, as if that problem isnt hard enough, how do several hosts share the same link when they all want to use it at the same time? To understand how hosts share a network, we need to introduce a fundamental concept, multiplexing, which means that a system resource is shared among multiple users. At an intuitive level, multiplexing can be explained by analogy to a timesharing computer system, where a single physical CPU is shared (multiplexed) among multiple jobs, each of which believes it has its own private processor. Similarly, data being sent by multiple users can be multiplexed over the physical links that make up a network. To see how this might work, consider the simple network illustrated in , where the three hosts on the left side of the network (senders S1S3) are sending data to the three hosts on the right (receivers R1R3) by sharing a switched network that contains only one physical link. (For simplicity, assume that host S1 is sending data to host R1, and so on.) In this situation, three flows of data—corresponding to the three pairs of hosts—are multiplexed onto a single physical link by switch 1 and then demultiplexed back into separate flows by switch 2. Note that we are being intentionally vague about exactly what a flow of data corresponds to. For the purposes of this discussion, assume that each host on the left has a large supply of data that it wants to send to its counterpart on the right. There are several different methods for multiplexing multiple flows onto one physical link. One common method is synchronous time-division multiplexing (STDM). The idea of STDM is to divide time into equal-sized quanta and, in a round-robin fashion, give each flow a chance to send its data over the physical link. In other words, during time quantum 1, data from S1 to R1 is transmitted; during time quantum 2, data from S2 to R2 is transmitted; in quantum 3, S3 sends data to R3. At this point, the first flow (S1 to R1) gets to go again, and the process repeats. Another method is frequency-division multiplexing (FDM). The idea of FDM is to transmit each flow over the physical link at a different frequency, much the same way that the signals for different TV stations are transmitted at a different frequency on a physical cable TV link. Although simple to understand, both STDM and FDM are limited in two ways. First, if one of the flows (host pairs) does not have any data to send, its share of the physical link—that is, its time quantum or its frequency—remains idle, even if one of the other flows has data to transmit. For example, S3 had to wait its turn behind S1 and S2 in the previous paragraph, even if S1 and S2 had nothing to send. For computer communication, the amount of time that a link is idle can be very large—for example, consider the amount of time you spend reading a web page (leaving the link idle) compared to the time you spend fetching the page. Second, both STDM and FDM are limited to situations in which the maximum number of flows is fixed and known ahead of time. It is not practical to resize the quantum or to add additional quanta in the case of STDM or to add new frequencies in the case of FDM. The form of multiplexing that we make most use of in this book is called statistical multiplexing. Although the name is not all that helpful for understanding the concept, statistical multiplexing is really quite simple, with two key ideas. First, it is like STDM in that the physical link is shared over time—first data from one flow is transmitted over the physical link, then data from another flow is transmitted, and so on. Unlike STDM, however, data is transmitted from each flow on demand rather than during a predetermined time slot. Thus, if only one flow has data to send, it gets to transmit that data without waiting for its quantum to come around and thus without having to watch the quanta assigned to the other flows go by unused. It is this avoidance of idle time that gives packet switching its efficiency. As defined so far, however, statistical multiplexing has no mechanism to ensure that all the flows eventually get their turn to transmit over the physical link. That is, once a flow begins sending data, we need some way to limit the transmission, so that the other flows can have a turn. To account for this need, statistical multiplexing defines an upper bound on the size of the block of data that each flow is permitted to transmit at a given time. This limited-size block of data is typically referred to as a packet, to distinguish it from the arbitrarily large message that an application program might want to transmit. Because a packet-switched network limits the maximum size of packets, a host may not be able to send a complete message in one packet. The source may need to fragment the message into several packets, with the receiver reassembling the packets back into the original message. In other words, each flow sends a sequence of packets over the physical link, with a decision made on a packet-by-packet basis as to which flows packet to send next. Notice that if only one flow has data to send, then it can send a sequence of packets back-to-back. However, should more than one of the flows have data to send, then their packets are interleaved on the link. depicts a switch multiplexing packets from multiple sources onto a single shared link. The decision as to which packet to send next on a shared link can be made in a number of different ways. For example, in a network consisting of switches interconnected by links such as the one in the decision would be made by the switch that transmits packets onto the shared link. (As we will see later, not all packet-switched networks actually involve switches, and they may use other mechanisms to determine whose packet goes onto the link next.) Each switch in a packet-switched network makes this decision independently, on a packet-by-packet basis. One of the issues that faces a network designer is how to make this decision in a fair manner. For example, a switch could be designed to service packets on a first-in-first-out (FIFO) basis. Another approach would be to transmit the packets from each of the different flows that are currently sending data through the switch in a round-robin manner. This might be done to ensure that certain flows receive a particular share of the links b andwidth, or that they never have their packets delayed in the switch for more than a certain length of time. A network that attempts to allocate bandwidth to particular flows is sometimes said to support quality of service (QoS), a topic that we return to in Chapter 6. Also, notice in that since the switch has to multiplex three incoming packet streams onto one outgoing link, it is possible that the switch will receive packets faster than the shared link can accommodate. In this case, the switch is forced to buffer these packets in its memory. Should a switch receive packets faster than it can send them for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped. When a switch is operating in this state, it is said to be congested. The bottom line is that statistical multiplexing defines a cost-effective way for multiple users (e.g., host-to-host flows of data) to share network resources (links and nodes) in a fine-grained manner. It defines the packet as the granularity with which the links of the network are allocated to different flows, with each switch able to schedule the use of the physical links it is connected to on a per-packet basis. Fairly allocating link capacity to different flows and dealing with congestion when it occurs are the key challenges of statistical multiplexing. 1.2.3 Support for Common Services While the previous section outlined the challenges involved in providing costeffective connectivity among a group of hosts, it is overly simplistic to view a computer network as simply delivering packets among a collection of computers. It is more accurate to think of a network as providing the means for a set of application processes that are distributed over those computers to communicate. In other words, the next requirement of a computer network is that the application programs running on the hosts connected to the network must be able to communicate in a meaningful way. When two application programs need to communicate with each other, there are a lot of complicated things that need to happen beyond simply sending a message from one host to another. One option would be for application designers to build all that complicated functionality into each application program. However, since many applications need common services, it is much more logical to implement those common services once and then to let the application designer build the application using those services. The challenge for a network designer is to identify the right set of common services. The goal is to hide the complexity of the network from the application without overly constraining the application designer. Intuitively, we view the network as providing logical channels over which application-level processes can communicate with each other; each channel provides the set of services required by that application. In other words, just as we use a cloud to abstractly represent connectivity among a set of computers, we now think of a channel as connecting one process to another. shows a pair of application-level processes communicating over a logical channel that is, in turn, implemented on top of a cloud that connects a set of hosts. We can think of the channel as being like a pipe connecting two applications, so that a sending application can put data in one end and expect that data to be delivered by the network to the application at the other end of the pipe. Thechallengeistorecognize what functionality the channels should provide to application programs. For example, does the application require a guarantee that messages sent over the channel are delivered, or is it acceptable if some messages fail to arrive? Is it necessary that messages arrive at the recipient process in the same order in which they are sent, or does the recipient not care about the order in which messages arrive? Does the network need to ensure that no third parties are able to eavesdrop on the channel, or is privacy not a concern? In general, a network provides a variety of different types of channels, with each application selecting the type that best meets its needs. The rest of this section illustrates the thinking involved in defining useful channels. Identifying Common Communication Patterns Designing abstract channels involves first understanding the communication needs of a representative collection of applications, then extracting their common communication requirements, and finally incorporating the functionality that meets these requirements in the network. One of the earliest applications supported on any networ Implementation of New Computer Network Implementation of New Computer Network Here we are going to implement an new computer network for this company that 25 employees have been working in. Suppose you want to build a computer network, one that has potential to grow to global proportions to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design t integrate these building blocks into an effective communication service? Suppose you want to build a computer network, one that has the potential togrow to global proportions and to support applications as diverse as teleconferencing, video-on-demand, electronic commerce, distributed computing, and digital libraries. What available technologies would serve as the underlying building blocks, and what kind of software architecture would you design to integrate these building blocks into an effective communication service? Answering this question is the overriding goal of — to describe the available building materials and then to show how they can be used to construct a network from the ground up. Before we can understand how to design a computer network, we should first agree on exactly what a computer network is. At one time, the term network meant the set of serial lines used to attach dumb terminals to mainframe computers. To some, the term implies the voice telephone network. To others, the only interesting network is the cable network used to disseminate video signals. The main thing these networks have in common is that they are specialized to handle one particular kind of data (keystrokes, voice, or video) and they typically connect to special-purpose devices (terminals, hand receivers, and television sets). What distinguishes a computer network from these other types of networks? Probably the most important characteristic of a computer network is its generality. Computer networks are built primarily from general-purpose programmable hardware, and they are not optimized for a particular application like making phone calls or delivering television signals. Instead, they are able to carry many different types of data, and they support a wide, and ever-growing, range of applications. This chapter looks at some typical applications of computer networks and discusses the requirements that a network designer who wishes to support such applications must be aware of. Once we understand the requirements, how do we proceed? Fortunately, we will not be building the first network. Others, most notably the community of researchers responsible for the Internet, have gone before us. We will use the wealth of experience generated from the Internet to guide our design. This experience is embodied in a network architecture that identifies the available hardware and software components and shows how they can be arranged to form a complete network system. To start us on the road toward understanding how to build a network, this chapter does four things. First, it explores the requirements that different applications and different communities of people (such as network users and network operators) place on the network. Second, it introduces the idea of a network architecture, which lays the foundation for the rest of the book. Third, it introduces some of the key elements in the implementation of computer networks. Finally, it identifies the key metrics that are used to evaluate the performance of computer networks. 1.1 APPLICATIONS Most people know the Internet through its applications: the World Wide Web, email, streaming audio and video, chat rooms, and music (file) sharing. The Web, for example, presents an intuitively simple interface. Users view pages full of textual and graphical objects, click on objects that they want to learn more about, and a corresponding new page appears. Most people are also aware that just under the covers, each selectable object on a page is bound to an identifier for the next page to be viewed. This identifier, called a Uniform Resource Locator (URL), is used to provide a way of identifying all the possible pages that can be viewed from your web browser. For example, http://www.cs.princeton.edu/~llp/index.html is the URL for a page providing information about one of this books authors: the string http indicates that the HyperText Transfer Protocol (HTTP) should be used to download the page, www.cs.princeton.edu is the name of the machine that serves the page, and /~llp/index.html uniquely identifies Larrys home page at this site. What most Web users are not aware of, however, is that by clicking on just one such URL, as many as 17 messages may be exchanged over the Internet, and this assumes the page itself is small enough to fit in a single message. This number includes up to six messages to translate the server name (www.cs.princeton.edu) into its Internet address (128.112.136.35), three messages to set up a Transmission Control Protocol (TCP) connection between your browser and this server, four messages for your browser to send the HTTP get request and the server to respond with the requested page (and for each side to acknowledge receipt of that message), and four messages to tear down the TCP connection. Of course, this does not include the millions of messages exchanged by Internet nodes throughout the day, just to let each other know that they exist and are ready to serve web pages, translate names to addresses, and forward messages toward their ultim ate destination. Another widespread application of the Internet is the delivery of streaming audio and video. While an entire video file could first be fetched from a remote machine and then played on the local machine, similar to the process of downloading and displaying a web page, this would entail waiting for the last second of the video file to be delivered before starting to look at it. Streaming video implies that the sender and the receiver are, respectively, the source and the sink for the video stream. That is, the source generates a video stream (perhaps using a video capture card), sends it across the Internet in messages, and the sink displays the stream as it arrives. There are a variety of different classes of video applications. One class of video application is video-on-demand, which reads a pre-existing movie from disk and transmits it over the network. Another kind of application is videoconferencing, which is in some ways the more challenging (and, for networking people, interesting) case because it has very tight timing constraints. Just as when using the telephone, the interactions among the participants must be timely. When a person at one end gestures, then that action must be displayed at the other end as quickly as possible. Too much delay makes the system unusable. Contrast this with video-on-demand where, if it takes several seconds from the time the user starts the video until the first image is displayed, the service is still deemed satisfactory. Also, interactive video usually implies that video is flowing in both directions, while a video-on-demand application is most likely sending video in only one direction. One pioneering example of a videoconferencing tool, developed in the early and mid-1990s, is vic. shows the control panel for a vic session. vic is actually one of a suite of conferencing tools designed at Lawrence Berkeley Laboratory and UC Berkeley. The others include a whiteboard application (wb) that allows users to send sketches and slides to each other, a visual audio tool called vat, and a session directory (sdr) that is used to create and advertise videoconferences. All these tools run on Unix—hence their lowercase names—and are freely available on the Internet. Many similar tools are available for other operating systems. It is interesting to note that while video over the Internet is still considered to be in its relative infancy at the time of this writing (2006), that the tools to support video over IP have existed for well over a decade. Although they are just two examples, downloading pages from the Web and participating in a videoconference demonstrate the diversity of applications that can be built on top of the Internet, and hint at the complexity of the Internets design. Starting from the beginning, and addressing one problem at time, the rest of this book explains how to build a network that supports such a wide range of applications. Chapter 9 concludes the book by revisiting these two specific applications, as well as several others that have become popular on todays Internet. 1.2 REQUIREMENTS We have just established an ambitious goal for ourselves: to understand how to build a computer network from the ground up. Our approach to accomplishing this goal will be to start from first principles, and then ask the kinds of questions we would naturally ask if building an actual network. At each step, we will use todays protocols to illustrate various design choices available to us, but we will not accept these existing artifacts as gospel. Instead, we will be asking (and answering) the question of why networks are designed the way they are. While it is tempting to settle for just understanding the way its done today, it is important to recognize the underlying concepts because networks are constantly changing as the technology evolves and new applications are invented. It is our experience that once you understand the fundamental ideas, any new protocol that you are confronted with will be relatively easy to digest. The first step is to identify the set of constraints and requirements that influence network design. Before getting started, however, it is important to understand that the expectations you have of a network depend on your perspective: An application programmer would list the services that his application needs, for example, a guarantee that each message the application sends will be delivered without error within a certain amount of time. A network designer would list the properties of a cost-effective design, for example, that network resources are efficiently utilized and fairly allocated to different users. A network provider would list the characteristics of a system that is easy to administer and manage, for example, in which faults can be easily isolated and whereitiseasytoaccountfor usage. This section attempts to distill these different perspectives into a high-level introduction to the major considerations that drive network design, and in doing so, identifies the challenges addressed throughout the rest of this book. 1.2.1 Connectivity Starting with the obvious, a network must provide connectivity among a set of computers. Sometimes it is enough to build a limited network that connects only a few select machines. In fact, for reasons of privacy and security, many private (corporate) networks have the explicit goal of limiting the set of machines that are connected. In contrast, other networks (of which the Internet is the prime example) are designed to grow in a way that allows them the potential to connect all the computers in the world. A system that is designed to support growth to an arbitrarily large size is said to scale. Using the Internet as a model, this book addresses the challenge of scalability. Links, Nodes, and Clouds Network connectivity occurs at many different levels. At the lowest level, a network can consist of two or more computers directly connected by some physical medium, such as a coaxial cable or an optical fiber. We call such a physical medium a link,and we often refer to the computers it connects as nodes. (Sometimes a node is a more specialized piece of hardware rather than a computer, but we overlook that distinction for the purposes of this discussion.) As illustrated in, physical links are sometimes limited to a pair of nodes (such a link is said to be point-to-point), while in other cases, more than two nodes may share a single physical link (such a link is said to be multiple-access). Whether a given link supports point-to-point or multiple-access connectivity depends on how the node is attached to the link. It is also the case that multiple-access links are often limited in size, in terms of both the geographical distance they can cover and the number of nodes they can connect. If computer networks were limited to situations in which all nodes are directly connected to each other over a common physical medium, then networks would either be very limited in the number of computers they could connect, or the number of wires coming out of the back of each node would quickly become both unmanageable and very expensive. Fortunately, connectivity between two nodes does not necessarily imply a direct physical connection between them—indirect connectivity may be achieved among a set of cooperating nodes. Consider the following two examples of how a collection of computers can be indirectly connected. shows a set of nodes, each of which is attached to one or more point- to-point links. Those nodes that are attached to at least two links run software that forwards data received on one link out on another. If organized in a systematic way, these forwarding nodes form a switched network. There are numerous types of switched networks, of which the two most common are circuit-switched and packet-switched. The former is most notably employed by the telephone system, while the latter is used for the overwhelming majority of computer networks and will be the focus of this book. The important feature of packet-switched networks is that the nodes in such a network send discrete blocks of data to each other. Think of these blocks of data as corresponding to some piece of application data such as a file, a piece of email, or an image. We call each block of data either a packet or a message, and for now we use these terms interchangeably; we discuss the reason they are not always the same in Section 1.2.2. Packet-switched networks typically use a strategy called store-and-forward. As the name suggests, each node in a store-and-forward network first receives a complete packet over some link, stores the packet in its internal memory, and then forwards the complete packet to the next node. In contrast, a circuit-switched network first establishes a dedicated circuit across a sequence of links and then allows the source node to send a stream of bits across this circuit to a destination node. The major reason for using packet switching rather than circuit switching in a computer network is efficiency, discussed in the next subsection. The cloud in distinguishes between the nodes on the inside that implement the network (they are commonly called switches, and their primary function is to store and forward packets) and the nodes on the outside of the cloud that use the network (they are commonly called hosts, and they support users and run application programs). Also note that the cloud in is one of the most important icons of computer networking. In general, we use a cloud to denote any type of network, whether it is a single point-to-point link, a multiple-access link, or a switched network. Thus, whenever you see a cloud used in a figure, you can think of it as a placeholder for any of the networking technologies covered in this book. A second way in which a set of computers can be indirectly connected is shown in . In this situation, a set of independent networks (clouds) are interconnected to form an internetwork, or internet for short. We adopt the Internets convention of referring to a generic internetwork of networks as a lowercase i internet, and the currently operational TCP/IP Internet as the capital I Internet. A node that is connected to two or more networks is commonly called a router or gateway, and it plays much the same role as a switch—it forwards messages from one network to another. Note that an internet can itself be viewed as another kind of network, which means that an internet can be built from an interconnection of internets. Thus, we can recursively build arbitrarily large networks by interconnecting clouds to form larger clouds. Just because a set of hosts are directly or indirectly connected to each other does not mean that we have succeeded in providing host-to-host connectivity. The final requirement is that each node must be able to state which of the other nodes on the network it wants to communicate with. This is done by assigning an address to each node. An address is a byte string that identifies a node; that is, the network can use a nodes address to distinguish it from the other nodes connected to the network. When a source node wants the network to deliver a message to a certain destination node, it specifies the address of the destination node. If the sending and receiving nodes are not directly connected, then the switches and routers of the network use this address to decide how to forward the message toward the destination. The process of determining systematically how to forward messages toward the destination node based on its address is called routing. This brief introduction to addressing and routing has presumed that the source node wants to send a message to a single destination node (unicast). While this is the most common scenario, it is also possible that the source node might want to broadcast a message to all the nodes on the network. Or a source node might want to send a message to some subset of the other nodes, but not all of them, a situation called multicast. Thus, in addition to node-specific addresses, another requirement of a network is that it supports multicast and broadcast addresses. The main idea to take away from this discussion is that we can define a network recursively as consisting of two or more nodes connected by a physical link, or as two or more networks connected by a node. In other words, a network can be constructed from a nesting of networks, where at the bottom level, the network is implemented by some physical medium. One of the key challenges in providing network connectivity is to define an address for each node that is reachable on the network (including support for broadcast and multicast connectivity), and to be able to use this address to route messages toward the appropriate destination node(s). 1.2.2 Cost-Effective Resource Sharing As stated above, this book focuses on packet-switched networks. This section explains the key requirement of computer networks—efficiency—that leads us to packet switching as the strategy of choice. Given a collection of nodes indirectly connected by a nesting of networks, it is possible for any pair of hosts to send messages to each other across a sequence of links and nodes. Of course, we want to do more than support just one pair of communicating hosts—we want to provide all pairs of hosts with the ability to exchange messages. The question, then, is how do all the hosts that want to communicate share the network, especially if they want to use it at the same time? And, as if that problem isnt hard enough, how do several hosts share the same link when they all want to use it at the same time? To understand how hosts share a network, we need to introduce a fundamental concept, multiplexing, which means that a system resource is shared among multiple users. At an intuitive level, multiplexing can be explained by analogy to a timesharing computer system, where a single physical CPU is shared (multiplexed) among multiple jobs, each of which believes it has its own private processor. Similarly, data being sent by multiple users can be multiplexed over the physical links that make up a network. To see how this might work, consider the simple network illustrated in , where the three hosts on the left side of the network (senders S1S3) are sending data to the three hosts on the right (receivers R1R3) by sharing a switched network that contains only one physical link. (For simplicity, assume that host S1 is sending data to host R1, and so on.) In this situation, three flows of data—corresponding to the three pairs of hosts—are multiplexed onto a single physical link by switch 1 and then demultiplexed back into separate flows by switch 2. Note that we are being intentionally vague about exactly what a flow of data corresponds to. For the purposes of this discussion, assume that each host on the left has a large supply of data that it wants to send to its counterpart on the right. There are several different methods for multiplexing multiple flows onto one physical link. One common method is synchronous time-division multiplexing (STDM). The idea of STDM is to divide time into equal-sized quanta and, in a round-robin fashion, give each flow a chance to send its data over the physical link. In other words, during time quantum 1, data from S1 to R1 is transmitted; during time quantum 2, data from S2 to R2 is transmitted; in quantum 3, S3 sends data to R3. At this point, the first flow (S1 to R1) gets to go again, and the process repeats. Another method is frequency-division multiplexing (FDM). The idea of FDM is to transmit each flow over the physical link at a different frequency, much the same way that the signals for different TV stations are transmitted at a different frequency on a physical cable TV link. Although simple to understand, both STDM and FDM are limited in two ways. First, if one of the flows (host pairs) does not have any data to send, its share of the physical link—that is, its time quantum or its frequency—remains idle, even if one of the other flows has data to transmit. For example, S3 had to wait its turn behind S1 and S2 in the previous paragraph, even if S1 and S2 had nothing to send. For computer communication, the amount of time that a link is idle can be very large—for example, consider the amount of time you spend reading a web page (leaving the link idle) compared to the time you spend fetching the page. Second, both STDM and FDM are limited to situations in which the maximum number of flows is fixed and known ahead of time. It is not practical to resize the quantum or to add additional quanta in the case of STDM or to add new frequencies in the case of FDM. The form of multiplexing that we make most use of in this book is called statistical multiplexing. Although the name is not all that helpful for understanding the concept, statistical multiplexing is really quite simple, with two key ideas. First, it is like STDM in that the physical link is shared over time—first data from one flow is transmitted over the physical link, then data from another flow is transmitted, and so on. Unlike STDM, however, data is transmitted from each flow on demand rather than during a predetermined time slot. Thus, if only one flow has data to send, it gets to transmit that data without waiting for its quantum to come around and thus without having to watch the quanta assigned to the other flows go by unused. It is this avoidance of idle time that gives packet switching its efficiency. As defined so far, however, statistical multiplexing has no mechanism to ensure that all the flows eventually get their turn to transmit over the physical link. That is, once a flow begins sending data, we need some way to limit the transmission, so that the other flows can have a turn. To account for this need, statistical multiplexing defines an upper bound on the size of the block of data that each flow is permitted to transmit at a given time. This limited-size block of data is typically referred to as a packet, to distinguish it from the arbitrarily large message that an application program might want to transmit. Because a packet-switched network limits the maximum size of packets, a host may not be able to send a complete message in one packet. The source may need to fragment the message into several packets, with the receiver reassembling the packets back into the original message. In other words, each flow sends a sequence of packets over the physical link, with a decision made on a packet-by-packet basis as to which flows packet to send next. Notice that if only one flow has data to send, then it can send a sequence of packets back-to-back. However, should more than one of the flows have data to send, then their packets are interleaved on the link. depicts a switch multiplexing packets from multiple sources onto a single shared link. The decision as to which packet to send next on a shared link can be made in a number of different ways. For example, in a network consisting of switches interconnected by links such as the one in the decision would be made by the switch that transmits packets onto the shared link. (As we will see later, not all packet-switched networks actually involve switches, and they may use other mechanisms to determine whose packet goes onto the link next.) Each switch in a packet-switched network makes this decision independently, on a packet-by-packet basis. One of the issues that faces a network designer is how to make this decision in a fair manner. For example, a switch could be designed to service packets on a first-in-first-out (FIFO) basis. Another approach would be to transmit the packets from each of the different flows that are currently sending data through the switch in a round-robin manner. This might be done to ensure that certain flows receive a particular share of the links b andwidth, or that they never have their packets delayed in the switch for more than a certain length of time. A network that attempts to allocate bandwidth to particular flows is sometimes said to support quality of service (QoS), a topic that we return to in Chapter 6. Also, notice in that since the switch has to multiplex three incoming packet streams onto one outgoing link, it is possible that the switch will receive packets faster than the shared link can accommodate. In this case, the switch is forced to buffer these packets in its memory. Should a switch receive packets faster than it can send them for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped. When a switch is operating in this state, it is said to be congested. The bottom line is that statistical multiplexing defines a cost-effective way for multiple users (e.g., host-to-host flows of data) to share network resources (links and nodes) in a fine-grained manner. It defines the packet as the granularity with which the links of the network are allocated to different flows, with each switch able to schedule the use of the physical links it is connected to on a per-packet basis. Fairly allocating link capacity to different flows and dealing with congestion when it occurs are the key challenges of statistical multiplexing. 1.2.3 Support for Common Services While the previous section outlined the challenges involved in providing costeffective connectivity among a group of hosts, it is overly simplistic to view a computer network as simply delivering packets among a collection of computers. It is more accurate to think of a network as providing the means for a set of application processes that are distributed over those computers to communicate. In other words, the next requirement of a computer network is that the application programs running on the hosts connected to the network must be able to communicate in a meaningful way. When two application programs need to communicate with each other, there are a lot of complicated things that need to happen beyond simply sending a message from one host to another. One option would be for application designers to build all that complicated functionality into each application program. However, since many applications need common services, it is much more logical to implement those common services once and then to let the application designer build the application using those services. The challenge for a network designer is to identify the right set of common services. The goal is to hide the complexity of the network from the application without overly constraining the application designer. Intuitively, we view the network as providing logical channels over which application-level processes can communicate with each other; each channel provides the set of services required by that application. In other words, just as we use a cloud to abstractly represent connectivity among a set of computers, we now think of a channel as connecting one process to another. shows a pair of application-level processes communicating over a logical channel that is, in turn, implemented on top of a cloud that connects a set of hosts. We can think of the channel as being like a pipe connecting two applications, so that a sending application can put data in one end and expect that data to be delivered by the network to the application at the other end of the pipe. Thechallengeistorecognize what functionality the channels should provide to application programs. For example, does the application require a guarantee that messages sent over the channel are delivered, or is it acceptable if some messages fail to arrive? Is it necessary that messages arrive at the recipient process in the same order in which they are sent, or does the recipient not care about the order in which messages arrive? Does the network need to ensure that no third parties are able to eavesdrop on the channel, or is privacy not a concern? In general, a network provides a variety of different types of channels, with each application selecting the type that best meets its needs. The rest of this section illustrates the thinking involved in defining useful channels. Identifying Common Communication Patterns Designing abstract channels involves first understanding the communication needs of a representative collection of applications, then extracting their common communication requirements, and finally incorporating the functionality that meets these requirements in the network. One of the earliest applications supported on any networ

Essay --

World War II was perhaps the most destructive war to plague the earth. The war took an unfathomable amount of lives some 17 million soldiers and a countless number of innocent civilians who died as a result of starvation and bombings, or Hitler's deliberate campaigns of mass murder through concentration camps. World War I helped to create some of the conditions that lead to the Second World War. The Treaty of Versailles was a peace agreement that was signed and took away the Central Powers of territory and arms from Germany, Austria, Turkey, Hungary, and Bulgaria. This left them with very heavy wartime reparations that needed to be paid, causing much bitterness. The war took a heavy toll on European economies and also helped with the unfortunate coming of the Great Depression. The Treaty also disappointed both Italy and Japan as Victors of the war. The Japanese attack on Pearl Harbor in Hawaii on December 7, 1941, set the stage for the United States entrance into the war. The surprise attack on the United States Navy by Japanese forces was intended as a preventative action in order to keep the US Pacific Fleet from interfering with military actions the Empire of Japan was planning in Southeast Asia against overseas territories of the United Kingdom, the Netherlands, and the United States. Almost at the same time, Japanese warplanes attack the Philippines and two U.S. islands: Wake and Guam, which are later occupied. Japanese troops invade Malaya and Thailand and seize Shanghai. Later in December Japanese troops invade Burma and Hong Kong. The United States declared war on Japan the following day, December 8, 1941. Japan entered into a war against the two most powerful navies in the world, the United States and Britain. Three da... ... a base for an expected invasion of Japan. US forces win in July and the US liberates Manila, Philippines after deadly and fierce street battles. Back over in Europe, US troops successfully cross the Rhine River and the Air Force use about 1,250 planes to lead the heaviest air raid against Berlin. The War in Europe is winding down and by April of 1945, the leader of Germany, Adolf Hitler, commits suicide, and by May, Germany surrenders. The United States is still at war with Japan and so on August 6, 1945, the first atomic bomb is dropped on Hiroshima and the second on August 9, 1945 on Nagasaki, killing well over 100, 000 people and causing the Japanese to surrender on August 14, 1945. The war ushered in the atomic age and was quickly followed by the collapse of the wartime alliance between the United States and the Soviet Union and the beginning of the Cold War.

The Role of Ancient Gods Essay -- essays research papers fc

When we study ancient Greek and Roman literature, we realize that the world perception in those times, among people, was much different from what it is now. It is especially obvious when we begin to analyze the role of mythical and religious elements in ancient literature. According to the classical Christian theological theory, people’s need for believing in supernatural beings is caused by their fear of nature. This concept strikingly resembles the Marxist explanation - it also names fear as the main factor. If one reads Homer’s â€Å"Iliad† and â€Å"Odyssey,† and Virgil’s â€Å"Aeneid†, he gets to realize that the ancient concept of people’s interaction with Gods is totally deprived of fear in any form. In all three masterpieces, Gods are basically described as humans, with all their strengths and weaknesses, although being immortal. Humans often revere Gods, but not out of fear – they simply respect their superiority. Many historians suggest that one of the main reasons, which enabled Greek and Roman civilizations to reach extraordinary heights in the fields of culture and science, is the fact of their religious liberalism. Let us to take a closer look at all three poems, so it’ll be easier for us to find common religious motives in all of them. Homer’s â€Å"Odyssey† is one of the finest examples of ancient Greek literature. Along with â€Å"Iliad† it represents an ultimate expression of ancient spirit, which we still use as a standard while assessing the cultural legacy of our own Western civilization. Modern historians doubt whether the same author wrote these two epic masterpieces. The main reason for this is that â€Å"Odyssey†, stylistically and conceptually, is much different from â€Å"Iliad†. First one is a high tragedy, its storyline based on the events of Trojan War. The style of this poem is very noble and there is no place for petty human weaknesses. The action takes place at the time when city of Troy was being besieged by Achaeans. Achaean leader Agamemnon takes Chrysies as his prize. She prays Apollo, who sends a plague on Achaeans. Achaean hero Achilles asks his mother sea-nymph Thetis to ask Zeus to punish Achaeans for being ignorant towards Achilles: â€Å"God of the silver bow, thy ear incline, Whose power encircles Cilla the divine; Whose sacred eye thy Tenedos surveys, And gilds fair Chrysa with distinguished rays! If, fired to vengeance at thy priest's request, Thy d... ...iter favors Aeneas. The God of Sea Neptune is also on the side of Aeneas, who’s able to safely reach the shores of Carthage, after storm dies down as a result of Neptune’s involvement. Among other Roman Gods that interact with Aeneas, we can name Mercury, Aeolus, Cupid, Allecto, Vulcan, Saturn and Minerva. The role of divine beings in all three poems can hardly be overestimated. What separates these poems from later Christian literature is the fact the Gods actively participate in people’s affairs and there is no judgment found on them†¦ Bibliography: 1.  Ã‚  Ã‚  Ã‚  Ã‚  Homer. â€Å"The Odyssey†. Translated by Fitzgerald, R. Garden City, NY, Anchor/Doubleday, 1961 2.  Ã‚  Ã‚  Ã‚  Ã‚  Homer. â€Å"The Iliad†. Translated by Lattimore, R. University of Chicago. 1951. 3.  Ã‚  Ã‚  Ã‚  Ã‚  Vergil. â€Å"Aeneid†. Translated by Williams. T. Boston. Houghton Mifflin Co. 1910. The Outline 1)  Ã‚  Ã‚  Ã‚  Ã‚  P. 1, Short introduction of the topic. 2)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 1 – 2, Homer’s â€Å"Iliad† analysis. 3)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 2 – 3, Homer’s â€Å"Odyssey† analysis. 4)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 3 – 4, Virgil’s â€Å"Aeneid† analysis. The Role of Ancient Gods Essay -- essays research papers fc When we study ancient Greek and Roman literature, we realize that the world perception in those times, among people, was much different from what it is now. It is especially obvious when we begin to analyze the role of mythical and religious elements in ancient literature. According to the classical Christian theological theory, people’s need for believing in supernatural beings is caused by their fear of nature. This concept strikingly resembles the Marxist explanation - it also names fear as the main factor. If one reads Homer’s â€Å"Iliad† and â€Å"Odyssey,† and Virgil’s â€Å"Aeneid†, he gets to realize that the ancient concept of people’s interaction with Gods is totally deprived of fear in any form. In all three masterpieces, Gods are basically described as humans, with all their strengths and weaknesses, although being immortal. Humans often revere Gods, but not out of fear – they simply respect their superiority. Many historians suggest that one of the main reasons, which enabled Greek and Roman civilizations to reach extraordinary heights in the fields of culture and science, is the fact of their religious liberalism. Let us to take a closer look at all three poems, so it’ll be easier for us to find common religious motives in all of them. Homer’s â€Å"Odyssey† is one of the finest examples of ancient Greek literature. Along with â€Å"Iliad† it represents an ultimate expression of ancient spirit, which we still use as a standard while assessing the cultural legacy of our own Western civilization. Modern historians doubt whether the same author wrote these two epic masterpieces. The main reason for this is that â€Å"Odyssey†, stylistically and conceptually, is much different from â€Å"Iliad†. First one is a high tragedy, its storyline based on the events of Trojan War. The style of this poem is very noble and there is no place for petty human weaknesses. The action takes place at the time when city of Troy was being besieged by Achaeans. Achaean leader Agamemnon takes Chrysies as his prize. She prays Apollo, who sends a plague on Achaeans. Achaean hero Achilles asks his mother sea-nymph Thetis to ask Zeus to punish Achaeans for being ignorant towards Achilles: â€Å"God of the silver bow, thy ear incline, Whose power encircles Cilla the divine; Whose sacred eye thy Tenedos surveys, And gilds fair Chrysa with distinguished rays! If, fired to vengeance at thy priest's request, Thy d... ...iter favors Aeneas. The God of Sea Neptune is also on the side of Aeneas, who’s able to safely reach the shores of Carthage, after storm dies down as a result of Neptune’s involvement. Among other Roman Gods that interact with Aeneas, we can name Mercury, Aeolus, Cupid, Allecto, Vulcan, Saturn and Minerva. The role of divine beings in all three poems can hardly be overestimated. What separates these poems from later Christian literature is the fact the Gods actively participate in people’s affairs and there is no judgment found on them†¦ Bibliography: 1.  Ã‚  Ã‚  Ã‚  Ã‚  Homer. â€Å"The Odyssey†. Translated by Fitzgerald, R. Garden City, NY, Anchor/Doubleday, 1961 2.  Ã‚  Ã‚  Ã‚  Ã‚  Homer. â€Å"The Iliad†. Translated by Lattimore, R. University of Chicago. 1951. 3.  Ã‚  Ã‚  Ã‚  Ã‚  Vergil. â€Å"Aeneid†. Translated by Williams. T. Boston. Houghton Mifflin Co. 1910. The Outline 1)  Ã‚  Ã‚  Ã‚  Ã‚  P. 1, Short introduction of the topic. 2)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 1 – 2, Homer’s â€Å"Iliad† analysis. 3)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 2 – 3, Homer’s â€Å"Odyssey† analysis. 4)  Ã‚  Ã‚  Ã‚  Ã‚  Pp. 3 – 4, Virgil’s â€Å"Aeneid† analysis.

How and why does Iago convince Othello of Desdmona’s infidelity?

Shakespeare is often referred to as the greatest playwright that ever lived. His comedies have made many laugh, his tragedies many have cried over and romances that have touched millions. Shakespeare's writing although hundreds of years old are always relevant to our lives because that is what they are about, life. Shakespeare deals with all aspects of human nature and flaws. He greatly exaggerates a particular flaw in each of his tragic heroes. This flaw brings about their downfall. In the course of one conversation Iago convinces a man who loves his wife completely that she is in fact having an affair with one of his most trusted subjects without using one shred of proof or any real basis. This is a man who can make the most innocent of people guilty and the most loved, hated. He uses many tactics to persuade Othello that Desdemona is cheating on him with Cassio, the reason, is revenge. Iago is a very cunning and manipulative man. He is also often irrational and erratic. He will go to any means to get what he wants and in this case he doesn't mind ruining three people in the process. At the beginning of the play we hear of Iago's rage at the fact that Cassio was made lieutenant instead of him. Iago feels that he was the better candidate and deserves the position. Iago isn't hard pushed to find a way of getting revenge. Othello often says that without Desdemona he would be in chaos, â€Å"But I do love thee; and when I love thee not, chaos is come again. † Iago uses this, because he wants to create chaos, which is one of the major themes of the play. Other major themes include relationships, jealousy, love and deceit. Luck provides him with the opportunity to stage an affair between Cassio and Desdemona, driving Othello to insanity and resulting in the death of Desdemona and Othello. Iago becomes very jealous of Othello because of his position in the Venetian Army. He is also sexually attracted to Desdemona but that is not a real reason for hating Othello, his mind concocts stories which he believes are true and thus making himself think acceptable to take revenge on Othello by sleeping with his wife. Iago believes that Othello has slept with his wife Emilia, â€Å"leapt into his seat†, he wants revenge for this too, â€Å"not out of absolute lust†. He wants to sleep with Desdemona for revenge not just for pleasure. He appears to be sexually frustrated as he also presumes that Cassio has also slept with Emilia, â€Å"I fear Cassio with me nightcap too†. Throughout the play he often refers to sex as lustful and nothing to do with love. This is emphasised in his disbelief that Othello and Desdemona's relationship is based on love. Through this we have to consider the reasons why he feels this way. Can he not love someone? He finds it easy enough to kill his own wife at the end of the play, yet is constantly reaffirming his â€Å"love† for Othello. We know he uses this as a tactic for Othello to gain faith in Iago, but could there be more? This plot is an obsession for Iago, his jealousy rules him. Could this mission be his only love? To understand how Iago convinces Othello that Desdemona is having an affair with Cassio we must look at the events beforehand which Iago directs to his own advantage. It starts when Cassio and Desdemona greet each other; Iago forms the plan that Cassio will be target. Cassio and Desdemona are friendly to each other and Iago can see how this could appear to be more than just friendship. Didst thou not see her paddle with the palm of his hand? † In Elizabethan times this was deemed as highly intimate and personal, this would have been an activity that only a couple would engage in. By claiming that Cassio was stroking Desdemona's hand, he is suggesting that they are a couple or intimate with each other. Iago sees the opportunity and uses his knowledge of Cassio to get him into a fight with Roderigo. Iago knows that this will outrage Othello and Cassio will want to redeem himself. Iago has planted the circumstances for Cassio to plead with Desdemona so that she will speak to Othello on Cassio's behalf. Iago knows that Desdemona will take up Cassio's plight for she is a good person. â€Å"I will beseech the virtuous Desdemona to undertake for me†. Desdemona doesn't realise that Iago is abusing her goodwill so that it will bring about her own downfall. Othello doesn't see it as strange that Desdemona is supporting Cassio for he knows what type of person she is. It is Iago that uses this as a basis for an affair between Cassio and Desdemona. Iago fools many of the main characters. He only gets away with this because they trust him and this protects him from any questioning. His cunning means that the events can occur, building the play. He uses this to his own benefit, talking Cassio into pleading with Desdemona and inducing Othello to believe that Desdemona is having an affair. Throughout the play Iago is described as an â€Å"honest† man, which to the audience seems ironic because really everything the man says they know to be a lie. Desdemona describes as, â€Å"o that's an honest fellow†, Othello thinks â€Å"This fellow's of exceeding honest,† and Cassio too sees him as honest, â€Å"†¦ honest Iago. † It surprises the audience that the characters are so blind to Iago's faults but then we must understand that he has never done anything that could make them doubt him. He is an idyllic picture, a man who is loyal and trustworthy, they could never imagine that he is capable of deceit. Iago's effectiveness at noticing innocent situations and making them look suspect is another way in which he gets Othello to believe in Desdemona's unfaithfulness. When Othello first enters the room at the start of Act III Scene III, Cassio hurriedly leaves the room after speaking with Desdemona. Cassio does this completely innocently, he leaves because he doesn't want to annoy Othello any more than he has already, he feels disgraced and is ashamed, and he cannot face Othello. Iago successfully twists this situation- â€Å"That he would steal away so guilty like- seeing you coming. † Iago explains Cassio's guilt as that he has been sleeping with Desdemona. Of course the reader knows that is not true, but to Othello, the way that he hurries away, once pointed out to him by Iago, does look very suspicious. This is even more enhanced in Othello's mind when immediately afterwards Desdemona starts defending Cassio and pesters Othello to re-instate him. This combined with Iago's perverting of the situation looks very abnormal to Othello. Iago convinces Othello that Desdemona is sleeping with Cassio by very through very calculated steps. In each instance he builds on Othello's insecurities and his trust in him. He is successful in commanding the lack of evidence to his own advantage. Othello trusts Iago as he sees him as a loyal subject. Iago starts by questioning Cassio and Othello's relationship. He does this by asking suggestive questions, â€Å"Did Michael Cassio, when you wooed my lady know of your love? † By doing this he is making Othello consider their past and what effect it could have on the present. When Othello questions him further he refuses to answer a question directly. â€Å"Honest my lord? † By doing this it is as if he is trying to protect Othello, by keeping something from him. This will make Othello want to know the truth even more as it is human nature to be curious; after all we all want to know details especially if you know that really you shouldn't hear it. For Othello to believe in what Iago is about to tell him Othello must trust him. Iago needs to know that his news will not be instantly dismissed, he does this by the affirmation of his love. † My lord you know I love you†. This is his basis, if you genuinely trust someone you believe in what they tell you. Othello and Iago had fought together in wars and it is most likely that they had often held each other's lives in their hands. So Othello would never believe that Iago would turn against him so suddenly, especially as for the large majority of the play, Iago looks to be nothing more than a completely loyal servant to Othello. He refuses to tell Othello what he's thinking. â€Å"Utter my thoughts? Why say they are vile and false? † He doesn't want to say anything bad or untrue, after all he is Othello's loyal servant and would not want to hurt him. He also doesn't want to leave himself out for blame by playing this way he can say that Othello pressurised the information out of him even when he wasn't sure it was true. Iago is good at planting ideas. † O beware my lord of jealousy†. Iago suggests what Othello should be thinking and feeling. Even if Othello wasn't previously jealous because maybe he didn't believe fully, now Iago has told him exactly what he should be feeling. By warning Othello has in fact put it in his utmost mind. Iago plays on the fact that Othello is not of Venetian society. He explains that there are differences in social attitudes. † In Venice they do not let God see the pranks they have not shown their husbands†. Othello cannot question this as he is from a different background and already feels compromised. Although when in Venice, he appears to be a strong-minded character, proves to have low self-esteem, this low opinion of himself may stem from being racially self-conscious. But some may argue that race would not have been an issue, it is more to do with the fact that he comes from a different society, an outsider who knows little of how their expectations. Although no mention is ever made of it, Othello views himself as different, which he is, from the rest of Venetian society. In was shock to everyone and probably even Othello that one of the most eligible women in Venice has fallen in love with him. So when Iago starts telling Othello of a relationship between Cassio and his wife, the rumours about Desdemona and the fact that she had refused men of higher status than Othello, â€Å"Not to affect many proposed matches of her own clime, complexion and degree†¦ † he believes it may be true. Also he reminds Othello of what her father said when he first found out about Desdemona planning to marry Othello without his consent- â€Å"Look to her Moor, if thou hast eyes to see: She has deceived her father and may thee†. To which Othello replies â€Å"My life upon her faith†. Much of Othello deals with pride and reputation, for Othello now to hear about Desdemona's unfaithfulness, after he replied so convincingly that he trusts her completely, would certainly start to worry him. After all, if what Iago had been telling Othello was true, then Othello had been made to look a complete fool by Desdemona in a very short period of time. Iago often uses very crude language and often refers to animal imagery. He belittles Othello and Desdemona's relationship, regarding it in its most instinctive form, a sexual relationship, â€Å"†¦ you'll have your daughter covered with a Barbary horse;† Othello however approaches it as serious and loving relationship, â€Å"†¦ Nor to comply with heat the young affects in me defunct and proper satisfaction; But to be free and bounteous to her mind. † That is why the audience is particularly amazed that Othello resorts to animalistic images too. Othello refers to Desdemona as â€Å"haggard†, a hawk that cannot be tamed. He also refers to himself as a â€Å"toad†; this is a far cry from the man who stood in front of the Duke and other important men of Venice declaring his love. Shakespeare uses this technique to show us that Othello has lost his confidence and is no longer self-assured. As he becomes more and more angry his control through his speech begins to slip, no longer does he speak in long flowing sentences but now in exclamations, which hints at his loss of capability to loose his temper. He is also speaking in a similar way to Iago, This may symbolise that he has come to think in the same manner. These images show us the depth of Othello's jealousy, the woman he loved he now disparage. When Othello begins to fall into the trap that Iago has set out, there is only one thing that would convince him completely. The principal method that Iago uses to convince Othello of Desdemona's infidelity is by using one of Othello's most treasured possessions and telling Othello that his wife, Desdemona has given it away to her lover, Cassio. The handkerchief was the first gift he gave to Desdemona, so it possesses enormous sentimental value to Othello. Finding out that Desdemona has given it away shows her as inimical. It must have hurt and angered him, after all the woman he loves and is married to has given away without a care for him, would almost certainly anger him, for in Othello's mind she has thought the handkerchief to be a meaningless piece of cloth. Iago tells Othello that he saw Cassio wiping his mouth with it, much like a rag. † I know not that; but such a handkerchief- I am sure it was your wife's- did I today. See Cassio wipe his beard with†. This enough proof for Othello to be convinced that Iago is telling the truth and for him to kill both Desdemona and Cassio. Within these three says let me hear thee say that Cassio's not alive. † And, â€Å"I will withdraw to furnish me with some swift means of death for the fair devil. † The fair devil refers to Desdemona. This oxymoron suggests that Othello still sees her as divine and yet he has lost his faith in her. Of course, the main way Iago fools Othello is by pure luck. That luck being that a lot of the things that Cassio and Desdemona say and do fall right into the trap and further convince Othello of a relationship between the two of them. When he first sees them together and Cassio scurries away, Iago jumps on the opportunity. Another example of this is found further on in the play when by controlling the circumstances Iago gets Cassio to talk disparagingly about Bianca, while Othello thinks the conversation is about Desdemona. The luck of this situation is gargantuan; one mention of the name Bianca and Othello would realise that Cassio was really speaking about her, fortuitously for Iago, Cassio does not mention Bianca's name once in the entire conversation. Shakespeare often presents the true feelings of the characters through soliloquies. Through Iago's soliloquy we see that Iago is an opportunist and amoral. The Moor already changes with my poison†¦ † This line shows that Iago's plan is having the desired effect. Other characters in Shakespeare's plays have shown conscience to the fact that they are doing wrong, and have felt some remorse, we can see this in Macbeth's soliloquy, â€Å"First, as I am his kinsman and his subject, strong both against the deed; then, as his host, who should against his murderer shut the door, not bear the knife myself. † But Iago shows no wavering, he is convinced that this is the right thing to do, â€Å"Burn like the mines of sulphur,† he wants Othello to fall from grace as revenge for instating Cassio over him. It is most disconcerting to think that Iago almost takes pleasure from Othello's torment, â€Å"Nor all the drowsy syrup of the world, shall medicine thee to that sweet sleep which thou ow'dst yesterday. † Othello is the typical â€Å"tragic hero† that Shakespeare incorporated in many of his works, a man who sets out to do his very best, but through one flaw he is bought down. This has an enormous effect on the audience. The audience know that he is a good man, but circumstances are working against him, leaving the audience frustrated at his own idiocy for not realising and making the amendments. Often as the audience we feel like screaming at him for being so blind to the facts, we are drained of our emotions. Shakespeare intended this; he used the ancient Greek method of Catharsis. Shakespeare had to make the main character likeable enough for the audience to warm to him and suffer his pain, but still make sure that in the end his tragic flaw shone through. Othello's main flaw is his jealousy. Othello's other flaws are pride and gullibility. Iago however can not be blamed for everything; he did not murder Desdemona nor kill Othello. The characters must have a motive of their own and therefore is there not a basis for Othello to be pushed into murdering his wife? Many would say that by removing Iago the couple would live happily ever after, but mustn't there be a reason for why Othello was pushed so readily into murder. Othello acts like a confident man when in Venice, he has the support of his wife and men like Cassio. Remove the safety of that support and you would find a man alone in a foreign country which has different values and expectations, maybe in reality Othello knew that he could not belong in Venetian society and not with Desdemona. Our view of Othello progresses as the play develops. The first mention of Othello is by Iago; he presents him to the audience as someone with poor judgement as he has promoted the wrong person and through repellent sexual images, as someone grotesque. Yet others, like the Duke see Othello as â€Å"†¦ valiant†¦ † From the beginning Othello is authoritative and confident, but without the knowledge that Desdemona is faithful to him, he collapses. Othello's lack of judgement is shown when he lets suspicion of Desdemona having an affair with Cassio take over his mind, stopping all rational thought. He asks the opinion of Emilia (Desdemona's handmaid and Iago's wife) â€Å"You have seen nothing then? † Even though she replied â€Å"Nor ever heard, nor ever did suspect† he does not believe her because his poisoned mind can't accept it. This is an issue that reigned in the Elizabethan times, people of his social status could not loose their power, it disrupted the hierarchy and made those below them feel uneasy. Society was very structured and those at the top would have a ripple effect on everyone below. We also notice in Shakespeare's plays that the tragic hero is always a man of position, Kings, noble men or army officials. This is so that they have a position to fall from, there would be no point in having an ordinary man in a story like this, the tragic hero is meant to be almost perfect, but not quite. This can be linked to the tragic hero King Lear; he is far too trusting and divides his country between his two treacherous daughters, which inevitably leads to his death. Through King Lear Shakespeare looks at madness and through the character of Othello he shows us how the people we surround ourselves with can create this. In the play, â€Å"King Lear†, King Lear has to deal with betrayal by his daughters in a similar way to which Othello is betrayed by his trusted friend, Iago and he believes his wife too. Like Othello Lear looks for justice instead of the revenge that Iago seeks. â€Å"It shall be done; I will arraign them straight. Come, sit thou here most learned justicer. â€Å"(King Lear, Act 3 scene 6) it indicates that a desire of order and justice is starting to replace the chaos and thoughts of savage revenge in Lear's mind; it marks the start of his journey away from insanity. This insanity is similar to what Iago creates in Othello, he creates jealousy and through that chaos. All of the main themes are present in Act III Scene III. The fight of good against evil is represented in Othello's struggle with Iago. The theme of chaos verses order is shown through Othello's gradual recede in anguish. Othello's overpowering jealousy blinding him from the truth and Iago's revenge which bring about the chaos and evil. Despite wanting to kill his wife Othello's love for her still remains. In his soliloquy before killing Desdemona he states his love for her, however Othello thinks murder is the only punishment worthy of betrayal â€Å"yet she must die, else she'll betray more men†. Othello's jealousy is now at peak level, he still can't show rational thought and is blind about the true horror he is about to do. Even when he speaks to her and she denies ever giving Cassio the handkerchief he doesn't believe her, â€Å"Yes, presently; therefore confess thee freely of thy sin; for to deny each article with oath cannot remove nor choke the strong conception that I do groan withal. Thou art to die. † It is ironic that Othello believes every lie that Iago fed him and yet cannot believe a single truth that the woman he loves tells him. â€Å"I never did offend you in my life; never lov'd Cassio but with such general warranty of heaven as I might love; I never gave him token. † After killing his bride he is brought out of his trance and realises the mistakes he has made. Iago's scheme is brought out into the open. Emilia brings out the scheme when the truth is told about the true goings on. At this point in the play Othello's heroic qualities are put on show for the audience once more. â€Å"Speak of me as I am; nothing extenuate, nor set down aught in malice: then, must you speak of one that lov'd not wisely but too well; of one not easily jealous, but, being wrought, perplex'd in the extreme. † Having realised the horror of the situation he takes full blame for his actions and commits suicide and lies next to his beloved bride to die. Iago is a man who is out for his own gain, and there are many people in our society who are like him. He is a character who knows how to direct circumstances to his own purpose, unfortunately the other character do not see this and are spun into his web of lies. By luck and tactics like planting ideas and evidence he is able to persuade Othello into thinking that Desdemona is having an affair and get his revenge. Through this catharsis we realise that in Iago Shakespeare has created that ultimate embodiment of evil and malice.