Waterboarding is Torture Essay - 1130 Words

A patrol team from the 1st Brigade, 3rd Infantry Division is responsible for searching suspected insurgent hideouts, capturing enemy combatants and bringing them in for questioning. On July 28th, 2011 the patrol team was in the city of Bagdad, Iraq when a roadside bomb takes out the first two vehicles in the convoy killing four soldiers. They immediately pull to the side of the road and take cover as the rest of the convoy comes under small arms fire. A long fight pursues, but the patrol team is able to disarm the insurgents and take them captive. The next day, back at camp, the platoon leader puts several soldiers from the patrol team in charge of interrogating one of the suspects. He explains the technique he wants used to obtain this†¦show more content†¦A rag is placed over their face to simulate darkness. Water is then poured over the rag, producing a lack of oxygen and inducing fear that makes the individual believe that they are going to die by drowning. In the event the person refuses to give up any information, they may be coerced to cooperate by using this extreme interrogation technique. In the weekly journal â€Å"Time U.S.†, the article â€Å"Waterboarding: A Mental and Physical Trauma† highlights the after-effects by people who have endured the traumatic experience of waterboarding. This is an utterly terrifying event, says Allen Keller, the director of the Bellevue/New York University School of Medicine Program for Survivors of Torture. Psychologically this can result in significant long-term post-traumatic stress, and produce anxiety and depression.† (Waterboarding: A Mental As Well As Physical Trauma - TIME.† N.p., n.d.) Allen Keller goes on to essentially refute claims that a subject intuitively understands that there is no real jeopardy, just discomfort by saying that there is a significant difference between waterboarding a subject during a training event and actual practice. In training, a student trusts that they will not be hurt. In contrast, a detainee has no such guarantee; therefore, the fear is a heightened reality. Many would believe that torture is considered an act that would only cause physical pain. However, physical punishment alone does notShow MoreRelatedArgumentative Essay On Waterboarding1071 Words   |  5 Pagesrecent waterboarding of prisoners of war, detainees and enemy combatants by the United States government has garnered much attention and debate. Some of main topics in this on-going debate include: Is waterboarding torture? Is it legal? Is it moral? What are the repercussions and possible reciprocal action of our enemies because of this waterboarding? This paper does not provide an argument for or against water boarding in and of itself but lays out a defense for the legality of waterboarding as wasRead MorePersuasive Essay On Torture929 Words   |  4 Pages The practice of torture by United States officials has become one of the most controversial elements of military history. The debate of its use in gathering intelligence has been particularly prevalent since the Bush administration. Most recently, a detailed and graphic scene of torture was presented in the movie Zero Dark Thirty. Proponents for the use of torture state that it is necessary for intelligence gathering and that ethics should be waved aside. Opponents argue that it is not becomingRead MoreUnited States Of Americ A Human Rights Defender For A Long Time Around The Global785 Words   |  4 Pages The United States of America had been known as a human rights defender for a long time around the global, but with the brutal torture actions performed by the Central Intelligence Agency, human rights that the America defended for so long seems to be questionable. Is it ok to violate international/ US laws as long as it benefits us? Moreover, does the so-called â€Å"enhanced† interrogation as effective as the CIA claims which helped gather valuable information from detainees that successfully help stoppedRead MoreAnalysis Of The Film Zero Dark Thirty 1122 Words   |  5 PagesThe film â€Å"Zero Dark Thirty† portrays the usage of torture being used to acquire information, which media enhances this torture to be favorable. The novel, Terrorism TV: Popular Entertainment in Post-9/11 America by Stacy Takacs, explores the â€Å"noble grunt† based upon how the information and the media merge together to allow viewers to think otherwise. â€Å"Zero Dark Thirty† directs a film based on a female actress who has her first experience for â€Å"the capture and killing of Osama bin Laden† through theRead MoreThe Moral Of Using Torture1108 Words   |  5 PagesThe Moral of Using Torture While torture is something some people would cringe at, others may approve of it as a useful tool. Is any government ever justified in using torture to gain information? Torture is defined as â€Å"the act of causing severe physical pain as a form of punishment or as a way to force someone to do or say something† (Merriam Webster 1). It has been used in various cultures throughout history such as China, Egypt, Iraq and many others, including modern America and VietnamRead MoreTorture Is Morally Justified?875 Words   |  4 Pages Torture interrogation has been used throughout history, more so recently at Guantanamo Bay with suspected terrorists. The big question is, are the answers that are obtained through torture interrogation reliable, and whether torture is morally justified? The purpose of this document is to explain what torture interrogation is, why it may be used, how it’s done, and how it affects reliability. To begin, torture is the intentional infliction of severe pain or suffering, both physically andRead MoreThe War On Terror Of Terrorism1384 Words   |  6 Pagesterrorists, pushes the boundaries of torture. The Merriam-Webster dictionary defines â€Å"torture† as â€Å"the act of causing severe physical pain as a form of punishment or as a way to force someone to do or say something† (â€Å"Torture†). However, in Alicia Shepherd’s article, Harsh Interrogation Techniques or Torture?, she indicates there is â€Å"no clear consensus on what constitutes torture† (Shepard). Yet while many still classify the techniques use by the CIA as actions of torture, that isn’t the phrase that isRead MoreEconomic Benefits Of Maternity Leave1558 Words   |  7 Pagescom, â€Å"Many against waterboarding as an illegal practice,.† Lauren Carroll, January 16, 2017 USAToday.com,â€Å"Waterboarding Didnt Work, Committee Report Finds.† Tom Vanden Brook, 10 Dec. 2014, Summary: Trump quote: â€Å"I would bring back waterboarding, and I’d bring back a hell of a lot worse than waterboarding,† Donald Trump believes that the US is not demonstrating its strength enough in the fight against ISIS. One of his suggested solutions as president is to revive waterboarding. Former presidentRead MoreThe Economic Benefits Of Paid Leave1616 Words   |  7 Pages â€Å"Many against waterboarding as an illegal practice,.† Lauren Carroll, January 16, 2017 USAToday.com,â€Å"Waterboarding Didnt Work, Committee Report Finds.† Tom Vanden Brook, December 10, 2014 Summary: Trump quote: â€Å"I would bring back waterboarding, and I’d bring back a hell of a lot worse than waterboarding,† Donald Trump believes that the US is not demonstrating its strength enough in the fight against ISIS. One of his suggested solutions as president is to revive waterboarding. Former presidentRead MoreThe United States War On Terror1158 Words   |  5 Pagesforefront of the nation’s agenda. This emergent wave of conflict required a different strategy than the those of the past because of the unorthodox nature of the opponent. One of the major innovations fostered by the â€Å"War on Terror† was the expansion of torture. The dramatic rise in terrorism sparked the unethical advancement of interrogation techniques in order to more effectively acquire information. The emergence of the â€Å"War on Terror† required government officials acquire intelligence in a new way thus

From Innocence to Experience - 1156 Words

From Innocence to Experience Transformations occur all throughout life, from developing pimples as an adolescent, to a midlife crisis that changes everything. In John Knowles’ novel A Separate Peace, there is a transformation in all key elements of the book, from the rivers, to the tree, to the characters. Three specific young men experience change not just because of the transitions through adolescence. These changes also come about because of war, an injury, and guilt. All of these transformations are specifically seen in Leper, Phineas, and Gene. A minor but vital character, Elwin Lepellier, a young man still trying to mature, gets thrown into war and is devoured by its viciousness. Elwin Lepellier or Leper is introduced as a†¦show more content†¦While recuperating at home, Gene stops by his house on his way back to Devon to tell Finny the truth, that it was his fault. However, Finny wouldn’t hear of it and later tells Gene that he wants him to go to the Olympics in his place. Gene feels an overwhelming sense of pride and exclaims â€Å"I lost a part of myself to him then, and a soaring sense of freedom revealed that this must have been my purpose from the first: to become a part of Finny† (77). Though no one can see it, Finny is faced with his own personal struggle: the bitterness of being a cripple and attempting to live in a world where sports and enlistment in the army are no longer a possibility. Finny undergoes surgery again after breaking the same leg and dies in the process. One may conclu de that his death was brought about more by the lack of will to live than anything else. Whereas Finny is confident and outgoing, Gene Forrester is a quiet, envious, introverted, and lonely young man. His insecurities are especially seen when Finny is around. Gene always chooses to argue or compete with Finny. An example of his competitive personality is seen when Finny says, â€Å"You were very good; once I shamed you into it†¦I am good for you that way. You have a tendency to back away from things otherwise.†(10). Gene responds, â€Å"You didn’t shame anybody into anything. I’ve never backed away from anything in my life.†(10). As time progress the rivalry increases and the tension inShow MoreRelatedCompare How Atonement and Spies Explore the Journey from Innocence to Experience.1460 Words   |  6 PagesCompare how Atonement and Spies explore the journey from innocence to experience. Both Atonement and Spies are bildungsroman where the protagonists are reminiscing about events in their childhoods which impose on them in their adult lives. In Atonement, Briony is narrating throughout the text; however the reader only finds this out at the end and in Spies Stephen is narrating with his older and younger self through duel narration with slippage between the two. Both text were published within a yearRead MoreA comparison of the Use of Language between the Chimney Sweeper from Songs of Innocence and Experience1198 Words   |  5 PagesA comparison of the Use of Language between the Chimney Sweeper from Songs of Innocence and Experience Even though, a hundred and seventy nine years later, lying in his grave, William Blake is still one of the best influences in poetry and even daily life today. Blake’s work, unrecognised during his lifetime, but now is almost universally considered that of a genius. Northrop Frye, who undertook a study of Blake’s entire opus, ‘What is in proportion to its merits the leastRead MoreThe Difference Between Innocence and Experience in Poetry670 Words   |  3 PagesThe Difference Between Innocence and Experience in Poetry The idyllic world of Innocence is exposed as naÃÆ've and foolish by the subversive cynicism of Experience. The world of Innocence is happy and loving, and can be compared to Arcadia and the Garden of Eden, the place of true innocence and lack of knowledge. However, Experience is actual reality of what living in the real world is actually like, where people have experienced the problems in the world. They are Read MoreTo Kill a Mockingbird Motiff Essay779 Words   |  4 PagesAll humans are born innocent. Innocence is a time when a person has never done something, it is the first step of a human beings existence. The second step is experience. This step happens after a person has done something he or she has never done before or learns something he or she has never know before. The motif of innocence and experience occurs many times in Harper Lee’s â€Å"To Kill a Mockingbird†. The process of this growth is especially obvious in Jem and Scout’s journey through out the bookRead MoreIgnorance Vs Ignorance1510 Words   |  7 PagesOften innocence is paired with ignorance, but there should be a divisible line between the two. Lacking knowledge on subjects that are erotic, inappropriate or unfavorable makes one innocent. It does not make them ignorant because they are still aware but choose not to speak on them. Ignorance can be the lack of knowledge on those matters as well, but has chosen to speak on them anyway. This is pernicious because it can strip innocence away. Innocence does not equal ignorance and being shelteredRead More An Analysis of Blakes The School Boy Essay1745 Words   |  7 PagesBlakes Songs of Innocence and Songs of Experience in its themes and imagery. Like many of the other poems in this work it deals with childhood and the subjugation of its spirit and uses imagery from the natural world. While first published in 1789 as one of the Songs of Innocence there are strong reasons why Blake moved it to the Experience1 section of the 1794 edition. If we compare it to other poems in the collection it sits better with others in Experience than those in Innocence. On firstRead More`` Candide `` : Innocence And Experience857 Words   |  4 Pagesthe Neo-classical novel Candide by Voltaire the theme of innocence and experience is prevalent through the protagonist, Candide, especially through his journey of finding the prescription of how to live a useful life in the face of harsh reality. In William Blake’s collection of Songs of Innocence and Songs of Experience the two characters, tyger and lamb, show how we lose our innocence to gain experience. Although the innocence and experience are paradoxical terms, we can solve the paradox by analyzingRead MoreInnocence and Experience1681 Words   |  7 Pageswe grew older that we began to lose our innocence with every new experience. Growing older means taking responsibility, accepting and overcoming life’s hardships and understanding oneself. So as we reach adulthood we begin to question when the conversion from innocence to experience occurs and what causes and marks this coming of a ge. In the novel They Poured Fire on Us From The Sky, the characters and plot prolong the opposition of innocence and experience and show us how they continuously overlapRead MoreTheme Of Innocence And Dr. Jekyll And Mr. Hyde1054 Words   |  5 PagesDuality Songs of Innocence Songs of Experience, by Blake, and Dr. Jekyll and Mr. Hyde, by Stevenson, are two stories, which present a case of duality. At the beginning of each of these novels, the author presents two different extremes: Blake presents innocence and experience and Stevenson presents good and evil. In both of these novels, as the story progresses, their two extremes struggle to coexist and one ultimately dominates over the other. Both Songs of Innocence Songs of Experience and Dr. JekyllRead MoreWilliam Blake s Poetry : Relationship Between Innocence And Experience1078 Words   |  5 Pagesin-depth the relationship between innocence and experience in his work, Songs of Innocence and Experience and the resulting tension between these two contrasting states. Blake demonstrates those in a state of innocence are oblivious of that state, ignorant of any other state of consciousness. However, those aware of innocence cannot honestly envision it because their perceptions of realit y have been colored by experience, which will stain their depictions of innocence as well. The subtitle underlining

Fundamental Causes, Inequity and Public Health Free Essays

Social injustice particularly that of [public] health, has been a constant pariah to the common society. Various ‘theories’ were posited as to the root cause of public health inequity; Phelan and Link (2005) directly associated the ‘fundamental’ causes of public health inequity with the ‘socioeconomic statuses (SES)’, the ‘social conditions’, the ‘gradients’ that existed therein. The fundamental cause lies on the material/ resources imbalance as the authors Phelan and Link (2005), Farmer (1999), and Lynch et al (2000) demonstrated. We will write a custom essay sample on Fundamental Causes, Inequity and Public Health or any similar topic only for you Order Now The fundamental causes of morbidity and mortality consist of: (1) influences to multiple disease outcomes, (2) operation through multiple risk factors, (3) intervening mechanism reproduce the association, and (4) finally, the most important feature of ‘fundamental causes’, it involves accession to resources that can be used to avoid risks or minimize the consequences of the disease involved. Health accession is shaped by extent of socio-economic resources (Phelan and Link, 2005). Here it is noted that the cognitive ability or intelligence cannot explain the relation between resource and health. SES, is, admittedly a ‘constant’ and persistent state of the general society (Phelan and Link, 2005). Not even the introduction of knowledge or the epidemiology of the disease was able to completely eradicate the health maladies present; instead, it seems to encourage health inequity. The US, a supra-economic world engine, has a systematic health care delivery system yet a relatively large proportion of their population—American Indians, Blacks and Hispanic and Asian immigrants—do not enjoy the benefits of the health care system as much as their rich counter parts. Localization of public health inequity is fed by the health biased terms like ‘Third World’, ‘Blacks’, ‘the poor’, and other terms that denote social stigma and racism . The aggravation of health inequity is destined to worsen with the current trend on ‘commodifying’ medicine and health and their ‘money-making’ participation in the market industry. Health inequity, as a result of multi-faceted elements of the society, is, as much as a disease as the feared bacillus ‘tubercle’, the causal agent of tuberculosis; Farmer (1999) illustrated the consumption of the disease agent ‘consuming the lives of the lower strata that existed in the late twentieth century. Farmer illustrates the case of societal ‘infection’ with different experiences of three stereotype tubercle patients—Jean Dubussoin (Haitian rural peasant), Corina Valdivia (Latin American with a multi-resistant drug strain of bacillus tubercle) and Calvin Loach (Afro-American and injection drug user). It was ‘social factors’ that determined the fate of these three-infected persons. Their struggle against their disease demonstrates the common obstacles they faced during health accession. Jean’s very low income and the long distance from the hospital dilapidated her chance at having a good accession to medical services offered. Corina’s case was exactly the same except that it demonstrated that of improper treatment of her disease and medical wariness. Calvin’s case was psychosocial wherein there was suggested wariness between him and the medical practitioner due to ‘[racial] wariness’ and late detection. Health inequity of tubercle bacillary patients does not stem from medical mismanagement, from physician-directed errors, as the three ‘stereotypes demonstrate, but more on the conglomeration of factors like race, income, economic policies, ease of health accession and fear of being apprehended or ignored by the medical staffs (Farmer, 1999). According to Lynch et al (2000), health inequity may also be associated with neomaterial interpretation —differential accumulation of exposures and experiences that have their sources in the material world—and differences in individual income. Health inequity, then, in general, is highly dependent on the resources of the individual. This is in opposition of the psychosocial theory which precludes that inequity is, more or less, a result of hierarchy stress or the combination of maladaptive behaviours as a reaction to the SES. The association between the standard of living and health cannot be easily dismantled, yet, on the face of such social health injustice, what actions are available for the State to remedy this particular problem? Lynch et al’s (2000) on solubilizing the problem was vague and inconclusive: .. trategic investments in neo-material conditions via more equitable distribution of public and private resources that are likely to have the most impact on reducing health inequalities and improving public health in both rich and poor countries in the 21st century†¦ (p. 1203) Farmer’s (1999) ultimate solution is pragmatic solidarity. The term was rather vague and inconclusive with no proper defin itum; Pragmatic solidarity was loosely defined as something that would mean ‘increased funding for control and treatment [of diseases]’, ‘making therapy available in a systematic way’ and preventing ‘emergence [of diseases]. Farmer’s primary intent is to target the health anathema at the specific level. On the other hand, Link and Phelan’s approach was different. Link and Phelan (2005) posited a barrage of solutions which capitalizes on policy consideration as macro-level approach to the problem— creating intervention that benefit state members irregardless of their own resources and actions, monitoring the dissemination of health enhancing information and interventions and creating policies that would distribute resources to the poor. A good solution to the problem would be targeting health inequity using combinatorial methods on the macro and micro-level approach. Interventions created at the larger scale such as policy consideration is a good approach and finding out the etiology of various diseases obviously have positive outcomes for ‘curing’. Such interventions are necessary to preserve not only the health of the general public but also to maintain a relatively pure, socially just and a healthy environment. How to cite Fundamental Causes, Inequity and Public Health, Papers

Computer Engineer free essay sample

After reading this chapter and completing the exercises, you will be able to: ? ? ? Describe the primary physical networking topologies in common use Describe the primary logical networking topologies in common use Describe major LAN networking technologies 109 Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 110 Chapter 3 Not so long ago, there was a real choice to be made between available network topologies and technologies when designing and building a new internetwork. Thankfully, this area of networking has gotten simpler rather than more complex, mainly because the choices have narrowed, with inferior or costly solutions becoming obsolete. This chapter discusses network topologies, which describe both the physical arrangement of cabling or pathways between network devices and the logical manner in which data is transferred from device to device. Next, you learn about network technologies or architectures that describe the methods computers use to transmit data to the networking medium in an orderly fashion. As you’ll see, the topology and technology are often tightly coupled, as certain technologies can be used only with certain topologies. The choices have been limited because only a few technologies and topologies remain as viable options. As is often the case, however, it helps to know where networking started to get an idea of where it might be heading. So even though some information covered in this chapter is obsolete or nearly so, your understanding of these older technologies will help you better understand current and future technologies. Physical Topologies The word â€Å"topology,† for most people, describes the lay of the land. A topographic map, for example, shows the hills and valleys in a region, whereas a street map shows only the roads. A network topology describes how a network is physically laid out and how signals travel from one device to another. However, because the physical layout of devices and cables doesn’t necessarily describe how signals travel from one device to another, network topologies are categorized as physical and logical. The arrangement of cabling and how cables connect one device to another in a network are considered the network’s physical topology, and the path data travels between computers on a network is considered the network’s logical topology. You can look at the physical topology as a topographic map that shows just the lay of the land along with towns, with only simple lines showing which towns have pathways to one another. The logical topology can be seen as a street map that shows how people actually have to travel from one place to another. As you’ll see, a network can be wired with one physical topology but pass data from machine to machine by using a different logical topology. All network designs today are based on these basic physical topologies: bus, star, ring, and point-to-point. A bus consists of a series of computers connected along a single cable segment. Computers connected via a central device, such as a hub or switch, are arranged in a star topology. Devices connected to form a loop create a ring. Two devices connected directly to one another make a point-to-point topology. Keep in mind that these topologies describe the physical arrangement of cables. How the data travels along these cables might represent a different logical topology. The dominant logical topologies in LANs include switching, bus, and ring, all of which are usually implemented as a physical star (discussed later in â€Å"Logical Topologies†). Physical Bus Topology The physical bus topology, shown in Figure 3-1, is by far the simplest and at one time was the most common method for connecting computers. It’s a continuous length of cable Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Physical Topologies 111 3 Figure 3-1 A physical bus topology network Courtesy of Course Technology/Cengage Learning  connecting one computer to another in daisy-chain fashion. One of this topology’s strengths is that you can add a new computer to the network simply by stringing a new length of cable from the last computer in the bus to the new machine. However, this strength is countered by a number of weaknesses: ? There’s a limit of 30 computers per cable segment. ? The maximum total length of cabling is 185 meters. ? Both ends of the bus must be terminated. ? Any break in the bus brings down the entire network. ? Adding or removing a machine brings down the entire network temporarily. ? Technologies using this topology are limited to 10 Mbps half-duplex communication because they use coaxial cabling, discussed in Chapter 4. Because of the preceding limitations, a physical bus topology is no longer a practical choice, and technology has moved past this obsolete method of connecting computers. However, the original Ethernet technology was based on this topology, and the basis of current LAN technology has its roots in the physical bus. So your understanding of bus communication aids your general understanding of how computers communicate with each other across a network. How Data Travels in a Physical Bus Two properties inherent in a physical bus are signal propagation and signal bounce. In any network topology, computers communicate with each other by sending information across the media as a series of signals. When copper wire is the medium, as in a typical physical bus, these signals are sent as a series of electrical pulses that travel along the cable’s length in all directions. The signals continue traveling along the cable and through any connecting devices until they weaken enough that they can’t be detected or until they encounter a device that absorbs them. This traveling across the medium is called signal propagation. However, even if a signal encounters the end of a cable, it bounces back and travels in the other direction until it weakens or is otherwise impeded. When a signal hits the end of a cable and bounces back up the cable’s length, it interferes with signals following it, much like an echo. Imagine if you were trying to communicate Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 112 Chapter 3 in an empty room with hard walls that caused your voice to echo continuously. The echo from the first words out of your mouth would garble the sound of words that followed, and your message would be unintelligible. The term used when electricity bounces off the end of a cable and back in the other direction is called signal bounce or reflection. To keep signal bounce from occurring, you do what you would to keep excessive echo from occurring; you install some type of material at both ends of the medium to absorb the signal. In a physical bus, you install a terminator, which is an electrical component called a resistor that absorbs the signal instead of allowing it to bounce back up the wire. Physical Bus Limitations Now that you know more about how a physical bus works, the previous list of weaknesses needs some additional explanation. The limitation of 30 stations per cable segment means only 30 computers can be daisy-chained together before the signal becomes too weak to be passed along to another computer. As an electrical signal encounters each connected workstation, some of its strength is absorbed by both the cabling and the connectors until the signal is finally too weak for a computer’s NIC to interpret. For the same reason, the total length of cabling is limited to 185 meters, whether there’s 1 connected station or 30 connected stations. The network can be extended in cable length and number of workstations by adding a repeater to the network, which, as you know, regenerates the signal before sending it out. At all times, both ends of the bus must be terminated. An unterminated bus results in signal bounce and data corruption. When a computer is added or removed from the network, both ends are no longer terminated, resulting in an interruption to network communication. For a small network of only a few computers, you might think a bus topology is fine, until you consider the last weakness listed: maximum bandwidth of 10 Mbps half-duplex communication. A physical bus uses coaxial cable (a cabling type discussed in Chapter 4, similar to what’s used in cable TV connections), which is limited to a top speed of 10 Mbps and communication in only half-duplex mode. Most of today’s networks use twisted-pair cabling, which can operate at 100 Mbps or faster and run in full-duplex mode, so communication between devices is much faster. For all these reasons, the physical bus topology has long since fallen out of favor and been replaced largely by the star topology, discussed next. Physical Star Topology The physical star topology uses a central device, such as a hub or switch, to interconnect computers in a LAN (see Figure 3-2). Each computer has a single length of cable going from its NIC to the central device. Some advantages of a physical star topology are the following: ? Much faster technologies are used than in a bus topology. ? Centralized monitoring and management of network traffic is possible. ? Network upgrades are easier. A physical star is the topology of choice for these reasons and more. With a central device, communication options are available that simply aren’t possible with a physical bus. For example, the central device can be a 100 Mbps hub, which increases a physical bus’s top Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Physical Topologies 113 3 Switch Figure 3-2 A physical star topology network Courtesy of Course Technology/Cengage Learning speed tenfold, or a switch, making it possible for multiple communication sessions to occur simultaneously and in full-duplex mode. As a budding network administrator, being able to monitor and manage your network with a central device is a big advantage over what was possible with a physical bus topology. Today’s hubs and switches can include software that collects statistics about your network traffic patterns and even alerts you when excessive errors or unusually high traffic rates are occurring on your network. You don’t get these features in a $19. 99 hub or switch, but  enterprise-level devices can be equipped with several network management tools. As long as your current cabling and installed NICs support it, your network can be upgraded quickly and easily from a ponderous 10 Mbps hub-based LAN to a blazing fast 100 Mbps or even 1000 Mbps switched network simply by replacing the central device. In addition, if your NICs must also be upgraded, you can upgrade in steps because most devices support multiple speeds. So if you want to upgrade from 100 Mbps to 1000 Mbps, you can replace the central device with a switch that supports both speeds, and then upgrade NICs as time and money allow. The switch transmits and receives on each port at the speed supported by the NIC connected to that port. What happens if the number of workstations you need to connect exceed the number of ports on the central device? In this case, you can connect hubs or switches, as you learned in Chapter 2. When several hubs or switches must be connected, usually one device is used as the central connecting point, forming an extended star. Extended Star The extended star topology, shown in Figure 3-3, is the most widely used in networks containing more than just a few computers. As the name implies, this topology is a star of stars. A central device, usually a switch, sits in the middle. Instead of attached computers forming the star’s arms, other switches (or hubs) are connected to the central switch’s ports. Computers and peripherals are then attached to these switches or Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 114 Chapter 3 Switch Switch Switch Switch Switch Figure 3-3 An extended star topology network Courtesy of Course Technology/Cengage Learning hubs, forming additional stars. The extended star is sometimes referred to as a â€Å"hierarchical star† because there are two or more layers of stars, all connecting back to the central star. The extended star can be used to connect many computers, with the central device running at a very fast speed to shuttle data between the LAN’s outer stars. This topology is most effective when the center of the star is running at a much faster speed than other devices; for example, the central device can run at 1000 Mbps while other devices run at 100 Mbps. How Data Travels in a Physical Star The details of how data travels from computer to computer in a physical star depend on the type of central device. Data transmission starts at a device at the end of one of the central device’s arms. From there, it travels along the network medium’s length until it arrives at the central device. As you know from learning how hubs and switches work, the transmission path differs, depending on the device. Other devices, such as multistation access units (MAUs) used in token ring networks, move data differently. The type of central device, therefore, determines the logical topology, discussed later in this chapter. Physical Star Disadvantages With all the clear advantages of a physical star, you might wonder whether there are any disadvantages. None outweigh the advantages, but it’s worth mentioning that the central device represents a single point of failure. In other words, if the hub or switch fails or  someone kicks the power cord out of the outlet, down goes the entire network. Thankfully, these devices tend to be reliable and are usually placed out of the way of everyday foot traffic. That being said, they do fail from time to time, and having a spare on hand is a good idea. When a physical bus was still the norm and the physical star was just coming on the networking scene in the late 1980s, it was often argued that because each computer must be Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Physical Topologies 115 cabled directly to the central device, instead of a bus’s daisy-chain arrangement, more cable was required to connect computers. This point is indeed true, and at the time, the amount of cabling needed was a factor in designing a network with a bus or star arrangement. By the time the star network’s advantages were fully realized in the mid-1990s, however, the cabling cost difference had diminished substantially, and the advantages clearly outweighed the minor cost disadvantage. Physical Ring Topology A physical ring topology is like a bus, in that devices are daisy-chained one to another, but instead of terminating each end, the cabling is brought around from the last device back to the first device to form a ring. This topology had little to no following in LANs as a way to connect computers. It was used, however, to connect LANs with a technology called Fiber Distributed Data Interface (FDDI). FDDI was most often used as a reliable and fast network backbone, which is cabling used to communicate between LANs or between hubs or switches. In Figure 3-4, the devices used to connect buildings form a ring, but computers on each LAN are connected with a physical star topology. Building C LAN switch FDDI hub Building A Building B Figure 3-4 A physical ring topology is usually used to connect LANs Courtesy of Course Technology/Cengage Learning The physical ring also had reliability issues because data had to be forwarded from one station to the next. Unlike a bus, in which data travels in all directions and is terminated at both ends, a ring doesn’t have any beginning or end. So each station must reproduce data and pass it along to the next station until it reaches the destination or the originator of the data. In other words, data always travels in one direction. If any station in the ring fails, data can no longer be passed along, and the ring is broken. Technologies such as FDDI overcome some problems with a physical ring network by creating a dual ring, in which data can travel in both directions so that a single device failure doesn’t break the entire ring. However, this technology is costly, and although it was used extensively in the 1990s and early 2000s because it was fast (100 Mbps) and reliable, 100 Mbps and 1000 Mbps Ethernet have largely supplanted it with an extended star technology. Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially  affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 3 116 Chapter 3 Point-to-Point Topology As its name implies, a point-to-point topology is a direct link between two devices. It’s most often used in WANs, in which a device on a business’s network has a dedicated link to a telecommunication provider, such as the local phone company. The connection then hooks into the phone company’s network to provide Internet access or a WAN or MAN link to a branch office. The advantage of this type of topology is that data travels on a dedicated link, and its bandwidth isn’t shared with other networks. The disadvantage is that this topology tends to be quite expensive, particularly when used as a WAN link to a distant branch office. Point-to-point topologies are also used with wireless networks in what’s called a wireless bridge. This setup can be used to connect two buildings without using a wired network (see Figure 3-5) or to extend an existing wireless network. Figure 3-5 A point-to-point wireless topology Courtesy of Course Technology/Cengage Learning A rudimentary LAN can also be set up with a point-to-point topology by connecting a cable between the NICs on two computers. Of course, this method allows only two computers on the network, but it can be used effectively for transferring files from one computer to another in the absence of a hub or switch. So as you can see, point-to-point topologies are used for specialized purposes. They aren’t commonly used in LANs; they’re used more often in WANs and large internetworks. Mesh Topology A mesh topology connects each device to every other device in a network. You can look at a mesh topology as multiple point-to-point connections for the purposes of redundancy and fault tolerance. Figure 3-6 shows a full mesh topology between four locations, with the switch in each location providing connectivity to multiple computers. Each switch is connected to every other switch, which is called a â€Å"full mesh. † If each switch were connected to only two other switches, it would be called a â€Å"partial mesh. † In either case, the purpose of creating a mesh topology is to ensure that if one or more connections fail, there’s another path for reaching all devices on the network. For example, in Figure 3-6, two connections could fail, but all devices could still communicate with one another. This type of topology is used mostly commonly in large internetworks and WANs, where routers or switches in multiple buildings or towns are connected in a partial or full mesh. Parts of the Internet are also designed with a partial mesh topology, in which major ISPs are connected so that even if one ISP’s network fails, data can bypass this part of the network to get to its destination. Mesh topologies, although reliable, are also expensive because of the additional cabling and ports required. In most cases, the ports used to connect devices are the highest speed available, such as 1 Gbps or 10 Gbps, and they often use expensive fiber-optic cabling for connecting buildings. Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Logical Topologies Chicago 117 New York WAN link 3 Los Angeles Phoenix Figure 3-6 Switches in each building are connected in a full mesh topology Courtesy of Course Technology/Cengage Learning Logical Topologies As mentioned, a network’s logical topology describes how data travels from computer to computer. In some cases, as with a physical bus and physical ring, the logical topology mimics the physical arrangement of cables. In other cases, as with a physical star, the electronics in the central device determine the logical topology. A network’s logical topology reflects the underlying network technology (covered later in â€Å"Network Technologies†) used to transfer frames from one device to one another. Table 3-1 summarizes the main logical topologies, the technologies using them, and the physical topologies for implementing them. Table 3-1 Logical topology Bus Logical topologies and associated network technologies and physical topologies Network technology Ethernet Physical topology Bus or star Wireless LANs Star Description A logical bus topology can be implemented as a physical bus (although this topology is now obsolete). When a logical bus is implemented as a physical star using wired Ethernet, the center of the star is an Ethernet hub. Whatever the physical topology is, data transmitted from a computer is received by all other computers. Wireless LANs use a physical star topology because they connect through a central access point. However, only one device can Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 118 Chapter 3 Table 3-1 Logical topology Logical topologies and associated network technologies and physical topologies (continued ) Network technology Physical topology Description transmit at a time and all devices hear the transmission, so a wireless LAN can be considered a logical bus topology. Ring Star Token ring networks use a central device called a multistation access unit (MAU or MSAU). Its electronics form a logical ring, so data is passed from computer to computer in order, until it reaches the destination device. FDDI Switched Token ring Ring As discussed, FDDI devices are connected in a physical ring, and data passes from device to device until it reaches the destination. Ethernet Star A switched logical topology using a physical star topology running Ethernet is by far the most common topology/technology combination now and likely will be well into the future. A switched topology creates dynamic connections or circuits between two devices whenever data is sent. This topology is  sometimes considered a switched point-to-point topology because a circuit is established between two points as needed to transfer data (like turning on a switch), and then the circuit is broken when it’s no longer needed (like turning off a switch). You have seen what a logical bus looks like when implemented as a physical bus. All computers are daisy-chained to one another, and network signals travel along the cable’s length in all directions, much like water flowing through interconnected pipes. When a logical bus is implemented as a physical star, the same process occurs, but the pathways are hidden inside the central hub. Figure 3-7 shows what a logical bus might look like when implemented with a hub. Signal Signal Logical bus inside a network hub Signal Signal Figure 3-7 A logical bus implemented as a physical star Courtesy of Course Technology/Cengage Learning Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the righ to remove additional content at any time if subsequent rights restrictions require it. Logical Topologies 119 A logical bus is sometimes called a â€Å"shared media topology† because all stations must share the bandwidth the media provides. A logical ring using a physical star implements the ring inside the central device’s electronics, which is an MAU in the token ring technology. Data is passed from one node or computer to another until it reaches the destination device (see Figure 3-8). When a port has no device connected to it, it’s simply bypassed, and data is sent out the next connected port. Figure 3-8 A logical ring implemented as a physical star Courtesy of Course Technology/Cengage Learning A switched topology works something like what’s shown in Figure 3-9. Although there’s always an electrical connection between the computer and switch, when no data is being transferred, there’s no logical connection or circuit between devices. However, when the switch receives a frame, a logical circuit is made between the source and destination devices until the frame is transferred. PC 4 PC 5 PC 6 No packets being transmitted PC 1 PC 2 PC 3 PC 1 and PC 6 communicate while PC 2 and PC 5 communicate Figure 3-9 The logical functioning of a switch Courtesy of Course Technology/Cengage Learning Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.