The Marco Polo Bridge Incident

The Marco Polo Bridge Incident of July 7 - 9, 1937 marks the start of the Second Sino-Japanese War, which also represents the beginning of World War II in Asia.  What was the incident, and how did it spark nearly a decade of fighting between two of Asias great powers?   Background Relations between China and Japan were chilly, to say the least, even prior to the Marco Polo Bridge Incident.  The Empire of Japan had annexed Korea, formerly a Chinese tributary state, in 1910, and had invaded and occupied Manchuria following the Mukden Incident in 1931.  Japan had spent the five years leading up to the Marco Polo Bridge Incident gradually seizing ever-larger sections of northern and eastern China, encircling Beijing.  Chinas de facto government, the Kuomintang led by Chiang Kai-shek, was based further south in Nanjing, but Beijing was still a strategically pivotal city. The key to Beijing was the Marco Polo Bridge, named of course for the Italian trader Marco Polo who visited Yuan China in the 13th century and described an earlier iteration of the bridge.  The modern bridge, near the town of Wanping, was the only road and rail link between Beijing and the Kuomintangs stronghold in Nanjing.  The Japanese Imperial Army had been trying to pressure China to withdraw from the area around the bridge, without success. The Incident In the early summer of 1937, Japan began to carry out military training exercises near the bridge.  They always warned the local inhabitants, to prevent panic, but on July 7, 1937, the Japanese commenced training without prior notice to the Chinese.  The local Chinese garrison at Wanping, believing that they were under attack, fired a few scattered shots, and the Japanese returned fire.  In the confusion, a Japanese private went missing, and his commanding officer demanded that the Chinese allow the Japanese troops to enter and search the town for him. The Chinese refused.  The Chinese army offered to conduct the search, which the Japanese commander agreed to, but some Japanese infantry troops tried to push their way into the town regardless.  Chinese troops garrisoned in town fired on the Japanese and drove them away. With events spiraling out of control, both sides called for reinforcements.  Shortly before 5 am on July 8, the Chinese allowed two Japanese investigators into Wanping to search for the missing soldier.  Nonetheless, the Imperial Army opened fire with four mountain guns at 5:00, and Japanese tanks rolled down the Marco Polo Bridge shortly thereafter.  One hundred Chinese defenders fought to hold the bridge; only four of them survived.  The Japanese overran the bridge, but Chinese reinforcements retook it the following morning, July 9. Meanwhile, in Beijing, the two sides negotiated a settlement of the incident.  The terms were that China would apologize for the incident, responsible officers on both sides would be punished, Chinese troops in the area would be replaced by the civilian Peace Preservation Corps, and the Chinese Nationalist government would better control communist elements in the area.  In return, Japan would withdraw from the immediate area of Wanping and the Marco Polo Bridge.  Representatives of China and Japan signed this accord on July 11 at 11:00 am. The national governments of both countries saw the skirmish as an insignificant local incident, and it should have ended with the settlement agreement.  However, the Japanese Cabinet held a press conference to announce the settlement, in which it also announced the mobilization of three new army divisions, and harshly warned the Chinese government in Nanjing not to interfere with the local solution to the Marco Polo Bridge Incident.  This incendiary cabinet statement caused Chiang Kaisheks government to react by sending four divisions of additional troops to the area.   Soon, both sides were violating the truce agreement.  The Japanese shelled Wanping on July 20, and by the end of July, the Imperial Army had surrounded Tianjin and Beijing.  Even though neither side likely had planned to go into an all-out war, tensions were incredibly high.  When a Japanese naval officer was assassinated in Shanghai on August 9, 1937, the Second Sino-Japanese War broke out in earnest.  It would transition into the Second World War, ending only with Japans surrender on September 2, 1945.

Yakuza - 1710 Words

Throughout the nineteenth and twentieth century, criminal organizations have begun to develop within various nations throughout the world. Some of these criminal organizations consist of various national and ethnic groups who centralized themselves as a single enterprise and various illegal activity which results in monetary gains, such as drug trafficking, racketeering, human trafficking, setting up illegal gambling establishments, and corrupting the local government with members of their own. For example, the Mexican drug cartels control one of the vast drug routes in Latin America while the Sicilian Mafia have set up a large protection racketing system throughout Italy. The Yakuza have established themselves in Japan and are†¦show more content†¦Members who violate codes and attack innocents such as family members and children are viewed as thugs by high rank members of the Yakuza and are expelled from the organization sometimes (77). A high ranking official from inside t he Yakuza has stated, â€Å" The Yakuza have existed this long because the police have allowed us to exist and we have cooperated with them to some extent. Those days are gone, as we are being replaced internally and externally by thugs and gangs who make no pretense in having codes at all.† (Kaplan 78). Many old generation Yakuza members believe the Yakuza itself has become deluded when various criminals who do not follow these codes of conduct join the organization. The traditional Yakuza members believe it is the reason why the Japanese government went after Yakuza. (79). The Yakuza, unlike most criminal organizations in the world, do not exist in secrecy. The Yakuza have made themselves public and have set many offices throughout Japanese, which are surrounded by barb and armed guards (43). They also have created printed business cards for their organization and published magazines detailing their criminal society. Some of their activities are actually legitimate business operations, such as running construction projects and various public works projects, real estate firms, and finance operations suchShow MoreRelatedMerits of Yakuzas1104 Words   |  5 Pagesï » ¿The yakuza - a family of organized crime that is complicated, hierarchical, underground and extremely influential in both the Private and the Public sphere, is unique to Japan. It is common knowledge that there exists an underworld in every country. The Yakuza, the significant part of Japan’s underworld however carries along unique characteristics, which makes it arguably a crucial part of what makes up the Japanese society. This essay seeks to substantiate the claim that Yakuzas, despite its definitionRead MoreAn Analysis Of Yakuzaian History, Beliefs, And Traditions1384 Words   |  6 Pageswhat today we know as the Yakuza surfaced: the shishi, the tekiya, and lastly the bakuto. It was the shishi that were commonly referred to as the strong arm protectors of the early modern state of Japan. They became increasingly disgruntled with the Tokugawa Shogunate which forced them to wage war against the government they swore to protect. The shishi did not outlast the Meiji Restoration period, but helped to instill loyalty in the later branches of the early Yakuza. The tekiya, who are alsoRead MoreYakuza and the Japanese Society1111 Words   |  5 PagesYakuza and Japanese society Essay building plan Sources: http://www.youtube.com/watch?v=bOazu1_NAZghttp://www.youtube.com/watch?v=bwvvjCXFv_Ihttp://www.neatorama.com/2011/03/20/the-yakuza-is-quietly-helping-earthquake-victims-in-japan/http://www.tumblr.com/tagged/ninkyodohttp://www.guardian.co.uk/world/2012/jan/05/japanese-yakuza-gangs-face-crackdown | 1. Introduction Introduction of the main question: What are the possible consequences of the implementation of the law? 2. Pros of havingRead MoreYakuza and the Japanese Society1123 Words   |  5 PagesYakuza and Japanese society Essay building plan Sources: http://www.youtube.com/watch?v=bOazu1_NAZghttp://www.youtube.com/watch?v=bwvvjCXFv_Ihttp://www.neatorama.com/2011/03/20/the-yakuza-is-quietly-helping-earthquake-victims-in-japan/http://www.tumblr.com/tagged/ninkyodohttp://www.guardian.co.uk/world/2012/jan/05/japanese-yakuza-gangs-face-crackdown | 1. Introduction Introduction of the main question: What are the possible consequences of the implementation of the law? 2. ProsRead MoreThe Yakuza a Large Crime Organization Essay654 Words   |  3 PagesOne is known for his occupation and what he does and what he withholds from doing. The yakuza is a large crime organization that has thousands of members that span throughout the entire world. They originated in Japan and since then have slowly moved across the globe into many different countries; they even have members in the United States today. *The yakuza is a highly organized crime organization that places great importance in respect and honor and seeks revenge when they do not receive it, theyRead MoreYojimbo1183 Words   |  5 Pagescapitalism. During this time in Japan, the Yakuza clan was a very strong and dangerous group equivalent to the modern day mafia. The Yakuza clans’ ideals are relatable to two themes prominent in Yojimbo: greed and corruption, and rising capitalist influence. Kurosawa satirizes these two characteristics of the Yakuza clan through the use of mise en scene. One way that Kurosawa used the mise en scene to satire the Yakuza clan was through the use of dà ©cor. The Yakuza clan was a group which took pride inRead MoreBecoming A Motorcycle Gang Of Course1299 Words   |  6 PagesBosozoku turned 20, most would likely become a low ranking member of the Yakuza, the organized crime scene of Japan (Tofugu). The Yakuza would often look to the Bosozoku for potential members of the Yakuza syndicates. To show the allegiance to the Yakuza boss, two rituals were required. The first of two dating back to the age of the Samurai, cutting off the tip of one’s left pinky was a sign of allegiance to the way of the Yakuza. This ritual was known as Yubitsume, this was done during the era of theRead MoreEssay about Japanese, Russian, Chinese, and Mexican Organized Crime1042 Words   |  5 Pagessuch as; extortion, white captive trafficking, automobile theft, counterfeiting, hostage taking, prostitution, weapons smuggling, murder, drug trafficking, and fraud. In Japan there is the Yakuza, also known as the Japanese Mafia, which consists of up to 2,500 families. The three largest groups in the Yakuza are the Yamaguchi-gumi, Sumiyaoshi-kai, and Inagawa-kai. These three groups together have around 61,100 members, or seventy-three percent of the gangster population in Japan. These organizationsRead MoreA Report on Japanese Culture Essay1086 Words   |  5 Pagesutensil. Subcultures: A facet that makes up the gem of the Japanese culture is called the Yakuza. The Yakuza are close to the organized criminal-underground of Europe and America called the Mafia. Both groups make their profits by numerous illegal activities. Drug trafficking, Gambling Rings, and extortion are just a few of the illicit affairs that are rules of trade for these groups. The Yakuza are also a part of the Japanese mythology. Within its secretive throng, the members are givenRead MoreThe Triad : Chinese Gangs868 Words   |  4 PagesBritain when the territory was still British owned in the 1970’s (Booth, 2000). In Japan, the yakuza have collaborated with multiple Triad groups to help smuggle immigrants, deal in credit card fraud, and forge passports. Because the Chinese Triads are historically known as very clever and ruthless, Triads operating from China are beginning to occupy and overthrow the yakuza, particularly in Tokyo. The yakuza allow the hostile take-over due to the belief that staying alive is the most important thing

Online Mba Programs Versus Traditional Bricks and Mortar Free Essays

string(314) " accredited by the Middle States Commission on Higher Education-access to campus-based and online libraries; career development assistance; academic advising; tutoring; financial aid advising-MBA \(available concentrations: Acquisition, Human Resource Management, Management, Marketing, Supply Chain Management\)\." Online MBA Programs versus On-site Programs Andrew Cortez Ashford Managerial Marketing BUS 620 Sharif Muhammad October 23, 2011 Online MBA Programs versus On-site Programs With unemployment rates at an all time high combined with the increasing costs associated with traditional brick and mortar schools, online education is by far one of the fastest growing and thriving industries. As younger students are attempting to pursue traditional higher education, they are realizing that the costs are not only increasing daily, but the programs are longer in duration and often not a better education than the online line programs. Those who have lost their jobs and need an edge over other unemployed candidates are finding that a B. We will write a custom essay sample on Online Mba Programs Versus Traditional Bricks and Mortar or any similar topic only for you Order Now A degree alone is often not enough and that in fact an MBA degree could greatly improve their chances as being more appealing to employers who have few jobs to offer to an overwhelming number of applicants. Those who do have jobs are often concerned about the stability of that job and this group is also is also looking towards those higher degree’s as to remain competitive and viable for their current jobs or for future jobs that may offer them more stability. This group typically has high work demands and as a result, they have to weigh their options when it comes to returning to school to obtain that MBA. The number of college level distance learning classes offered online continues to increase as they offer greater scheduling flexibility to students, they appeal to students who like to work independently, and allow colleges to increase enrollment without building new classrooms (Werhner, 2010, p. 310). Understanding fully what your goals are, as well as what limits you may have will help to determine the right direction for a student. The following will include a marketing plan that will assist in demonstrating the advantages of perusing an online MBA program as a viable and preferred alternative to an on-site MBA Program. 1. Company Overview: San Diego Higher Education (SDHE) is an online, for Profit Company that focuses on online education with the purpose serving its students as a viable method of obtaining an MBA degree via web-based courses through an accredited university. With the SDHE online MBA program, you can have the skills and experience you need to increase your chances for success by taking on the most complex leadership roles. SDHE has been assisting San Diego residents in obtaining an MBA degree using the online medium since 2007. The company had initially targeted low income and or unemployed individuals, but it has expanded its offerings with the intent to grow towards all segments. Beyond practical skills, the program is also designed to foster thought leadership, innovation, and corporate social responsibility on a multinational, multicultural scale; SDHE is headquartered in San Diego California. Key Leaders of the company: Tanner C. Dean-CEO †¢ Jeffery S. Anderson-CFO †¢ Scott R. Howard-COO †¢ Andrew Cortez-CMO Key Service Offerings: Online MBA programs with a specialization in Finance, Healthcare Marketing, Project Management, Human Resources, Information Technology, Global Management and Accounting. 2. Executive Summary of Marketing Plan: As the economy has continued to decline and unemployment has continued to increase, the need for affordable and accessible online educational optio ns have increased. The use of on-line instructional delivery methods by non-traditional adult learners continues to grow as technological and societal changes have enabled and encouraged this growth. The purpose of this marketing plan is to review recent marketing strategies with respect to how adults learn and tie that strategy into a discussion based upon a review of the suitability of, satisfaction with, and preference towards on-line instruction among adults. Some areas for improvement are discovered and recommendations are provided based upon these reviews (McGlone, 2011, p. 1-9). It is expected that our marketing efforts need realignment as to become more relevant to all types of students. Where as our initial marketing plan was very narrow, the market has since completely opened up and we now are in a position expand our offerings to larger audience. We will propose to re-brand and redirect our SDHE as to appeal to a much broader demographic segment. The ultimate goal is to convince potential students that SDHE is a viable higher education institution that exceeds the offerings of our competitors while maintaining a lower cost for an MBA degree. Our niche is that we are in fact a smaller institution and can therefore offer a more customized program in which students do not feel as though they are just a source of revenue for our company; they will feel as though they are receiving critical and accessible services that they will not receive from the larger institutions. 1. Description of Target Market: Demographic Segment: Male/Females between the ages of 22-45+ who have an understudy degree, income 35K-80K per year. Psychographic Segment: Looking towards individuals who come from industries that have been most impacted by economy, such as real estate, banking, construction. , retail, home improvement, pharmaceuticals, marketing, cell phone, and automotive industries (Rampell, 2009). Geographic Segment: Target for this particular marketing plan should include California, Nevada, Florida, Arizona, Idaho and Louisiana as these states have been hit hardest by the recession (Kiser, 2010). Out of these states we need to look at specific demographics of these states as to assure that they are in alignment with our Demographic Segment, if they may be eliminated. . Description of Competitors: University of Phoenix: The University of Phoenix is accredited by The Higher Learning Commission and is a member of the North Central Association-access to campus-based and online libraries; academic advising; mentoring; tutoring; financial aid office-MBA (concentrations include: Accounting, e-Business, Global Management, Health Care Mana gement, Human Resource Management, Marketing, Technology Management); joint MS in Nursing with MBA in Health Care Management. Every University of Phoenix faculty must have a Masters or Doctorate degree. No classroom attendance, the curriculum is completely online. Strayer University: Strayer University is accredited by the Middle States Commission on Higher Education-access to campus-based and online libraries; career development assistance; academic advising; tutoring; financial aid advising-MBA (available concentrations: Acquisition, Human Resource Management, Management, Marketing, Supply Chain Management). You read "Online Mba Programs Versus Traditional Bricks and Mortar" in category "Papers" Baker online: Baker College is accredited by the Higher Learning Commission and is a member of the North Central Association through Baker College-access to campus-based and online libraries; career counseling and placement assistance; academic advising-MBA (available concentrations: Accounting, Computer Information Systems, Finance, General Business, Health Care Management, Human Resource Management, Industrial Management, International Business, Leadership Studies, Marketing) Columbia Southern University: Distance Education Training Council (DETC) – Online library with 24-7 librarian services, academic and financial aid advising, and student services-General concentration, optional concentrations (E-Business and Technology, Finance, Health Management, Hospitality and Tourism, Human Resource Management, International Management, Marketing, Project Management, Public Administration, Sport Management). 3. 0 Description of Product or Services: SDHES’S MBA program refines the existing skills that the students already posses. Through our unique 18 month program students can complete the entire program and earn their MBA. The program will provide a solid understanding in all areas of business, from the fundamentals to specializations in Finance, Healthcare Marketing, Project Management, Human Resources, Information Technology, Global Management and Accounting. The specializations will give students the opportunity to deepen their knowledge by focusing on their specific areas of interest. The entire program is online and students are designed for the busy schedules of its students. . Marketing Budget: This particular budget is for a twelve month re-launch and re-branding of its current offerings as to expand our current customer base. The amount required for this is $960K and the break down of expenses is as follows: †¢ $120K-Website update to include up to date and current functionality. †¢ $600k- Media to include social media campaign (Banner ads/email blasts/news letters) to correspond with Bil lboard, television and print add. †¢ $120K- Marketing items to include flyers, inserts, sales brochures and misc. ollateral as deemed per region. †¢ $60K- PR to include press releases, public appearances etc. †¢ $60K- Outreach to local business, to include employment agencies. Outreach will be a more grass roots approach to specific communities. 5. Description and Location: Online academics can open itself to a much larger market segment as the virtual classrooms are much larger than a traditional class room. Because the MBA program would be completely online it is available to anyone with the technology of a computer and internet service. Internet/ web site searches are the key locations where potential students will initially look for our product; this is why so much of the budget will be spent on website design and functionality. Distribution channels such as face book and Google banners will be used. Street teams will be used at trade fairs, conventions and job fairs. We will also offer larger corporations incentives to post information on their internal websites advertising educational resources to their employee’s. Mall Media will also be used to advertise; larger regional malls can have up to 1 million + in monthly foot traffic, this medium is often more effective than traditional billboards as the customer is walking slowly and more likely to see our advertisement. 6. Pricing: Identifying the pricing the appropriate pricing category for our program should be very easy as we will remain competitive but we will still remain on the lower side. With so many online schools that currently in operation, potential students do have several options available. Because we are in a tough economic climate, pricing is more crucial than in previous years. Yes, benefits and features are extremely important as well, which is why will not be the lowest but will be towards the bottom from a pricing perspective. We will also offer discounts to certain corporation whom we will be partnering up with and in addition we will be offering a military discount as well. The current pricing range for online MBA programs range anywhere from 60k to 20k and so our pricing will at about 30K for the program, not including course materials, technology fee’s etc. This competition oriented method of pricing will make us very appealing to our potential students, while still allowing us as a company to remain profitable. 7. Summary and Implementation: In order to maximize new student enrollment we must stay ahead of the competition. We are an online school and so our online presence needs to be the area of most focus, from a marketing perspective. Our website needs to be as intuitive and easy to navigate as possible; it must draw the customers in and connect with them. This being said, an overall marketing campaign that is in line with the new website is essential. We must remain focused, within this campaign, on the ease and accessibility that our online MBA can provide them with all while being priced very competitively. Our efforts must be geared towards the quality of the education as we will be compared side by side to our direct competitors, our demographics are very computer savvy and so it is important that we remain a viable option through a flawless reputation. We shall also be strategic with the timing of the implementation of this marketing plan by researching unemployment trends to help us to determine timing (probably at the in December and January). In addition; we want to want to make sure that we are capturing the fresh graduates and so the months of April-June are months to focus on as well. This re-launch is something to be very excited about. We need internal by in from all departments. With flawless execution this marketing plan has the potential to increase our bottom line profits by up to 20% over last year. References Kiser, G. (2010, March 23). The Cities Hit Hardest by the Recession: Brookings Institution [Business]. Huffington Post. Retrieved from http://www. huffingtonpost. com/2010/03/23/the-cities-hit-hardest-by_n_509744. tml#s75345title=1_Cape_Coral McGlone, J. R. (2011). Adult Learning Styles and Online Educational Preference [Journal]. Research in Higher Education Journal, 12, 1,9. Rampell, C. (2009, January 26). Layoffs Spread to More Sectors of the Economy [Money Matters]. The New York Times. Retrieved from http://www. nytimes. com/2009/01/27/business/economy/27layoffs. html Werhner, M. J. (2010). A Compariso n of the Performance of Online versus Traditional On-Campus Earth Science Students on Identical Exams []. Journal of Geoscience Education, 58(5), 310-313. How to cite Online Mba Programs Versus Traditional Bricks and Mortar, Papers

Drilling For Oil In The Arctic Wildlife free essay sample

Refuge Essay, Research Paper The inquiry of whether to bore for oil in the Arctic National Wildlife Refuge stands clearly on the energy issues tabular array. The Arctic National Wildlife Refuge is a 1.5 million-acre package of wilderness country surrounding the Arctic Ocean to the North and the Trans-Alaska Pipeline to the South. The Arctic National Wildlife Refuge is presently off bounds to oil geographic expedition and production. Because of the ecological hazardsHow much oil is in the Arctic National Wildlife Refuge? In May 2000, the Energy Information Administration released it # 8217 ; s most recent publication, Potential Oil Production from the Coastal Plain of the Arctic National Wildlife Refuge: Updated Assessment, May 2000 which concluded, # 8220 ; This is the largest undiscovered, potentially productive onshore basin in the United States # 8230 ; ..There is a 95 per centum chance that at least 5.7 billion barrels of oil are recoverable. # 8221 ; Security statements fundamentally break down into a inquiry of U.S. dependance on oil imports. We will write a custom essay sample on Drilling For Oil In The Arctic Wildlife or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page While mutuality best characterizes the whole of planetary political dealingss, with no province able to exercise entire independency in any economic, environmental or security affair, the inquiry of oil dependance historically ranks high on the U.S. national security docket. In the past three decennaries, for illustration, the United States populatio N has experienced both the Persian Gulf and an oil initiated planetary fiscal crises. Environmental concerns attached to the Arctic National Wildlife Refuge oil production shows concerns expressed about oil production in the United States throughout the past three decennaries. Along with specific concerns linked to production accidents and ecosystem stableness, the issue of an oil based fossil-fueled economic system besides raises inquiries in the international environmental kingdom. Increased oil geographic expedition and production activities at the Arctic National Wildlife Refuge besides pose possible jobs for the full Arctic part ecosystem.Given the continued diverseness of the planetary oil market, and awaited production additions all around the universe, it does non look to step beyond the kingdom of rationality to propose stableness in American national security with regard to future oil imports without the Arctic National Wildlife Refuge oil boring. If there were a 95 % opportunity of retrieving at least 5.7 billion barrels of oil in the Arctic National Wildli fe Refuge and the United States imports about 7 million barrels of oil per twenty-four hours, the Arctic National Wildlife Refuge oil would merely account for two old ages worth of oil imports. What we see go oning today with regard to the oil market is truly no oil deficit, merely a temporarily lag in oil production.

Essay Examples on Advantages and Disadvantages of Internet Essay Example

Essay Examples on Advantages and Disadvantages of Internet Paper 1st Essay Sample on Advantages and Disadvantages of Internet Have you ever wondered what would happen if Internet didn’t exist in this world ? Explanation Internet is now commonly used by people all ages all over the globe. It has various functions that benefit human beings from communication to entertainment. Reasons Advantages receive and find the latest information online Purchasing newspapers and magazines won’t be necessary anymore because all the most recent news will show up in front of our eyes with just a single click. Completing projects and assignments would also be much more easier as we can find tons of useful information on the Internet. Share photos and videos online through social medias we get to share our experiences and interact with people anytime, anywhere complete a lot of things by using the Internet without leaving the house such as online banking, online shopping, online gaming and online billing. All these functions make our life much more convenient. Disadvantages tears people apart because they only meet in social networks and not meeting each other in person This is accurate because people nowadays, especially youngsters, get addicted to playing online games as well as social media chatting instead of interacting with people in real life. Advantages and Disadvantages of Internet Advantages and Disadvantages of Internet Advantages and Disadvantages of Internet This causes an individual to be less sociable in reality and it worsens relationships between family and friends. Risk a theft to our personal information if we use the Internet for online banking Imposter can trick us into doing inappropriate things and even hijack our money if we’re not careful some dishonest vendors sell low quality goods to their customers. The products in pictures may seem appealing but when the stock arrives, it contains flaws. Conclusion Personal Comments To sum up, there are both advantages and disadvantages to using the Internet. I believe it can be a good thing as long as people use it wisely. 2nd Essay Sample on Advantages and Disadvantages of Internet We will write a custom essay sample on Essay Examples on Advantages and Disadvantages of Internet specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Essay Examples on Advantages and Disadvantages of Internet specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Essay Examples on Advantages and Disadvantages of Internet specifically for you FOR ONLY $16.38 $13.9/page Hire Writer Rhetoric Question Have you ever wondered what would happen if Internet didn’t exist in this world ? Explanation Internet is now commonly used by people all ages all over the globe. It has various functions that benefit human beings from communication to entertainment. Reasons Advantages receive and find the latest information online Purchasing newspapers and magazines won’t be necessary anymore because all the most recent news will show up in front of our eyes with just a single click. Completing projects and assignments would also be much more easier as we can find tons of useful information on the Internet. Share photos and videos online through social medias we get to share our experiences and interact with people anytime, anywhere complete a lot of things by using the Internet without leaving the house such as online banking, online shopping, online gaming and online billing. All these functions make our life much more convenient. Disadvantages tears people apart because they only meet in social networks and not meeting each other in person This is accurate because people nowadays, especially youngsters, get addicted to playing online games as well as social media chatting instead of interacting with people in real life. Advantages and Disadvantages of Internet Advantages and Disadvantages of Internet Advantages and Disadvantages of Internet This causes an individual to be less sociable in reality and it worsens relationships between family and friends. Risk a theft to our personal information if we use the Internet for online banking Imposter can trick us into doing inappropriate things and even hijack our money if we’re not careful some dishonest vendors sell low quality goods to their customers.

Learning and Personal Development Plan Essay

Learning and Personal Development Plan Essay Learning and Personal Development Plan Essay Introduction to personal development in health, social care or children’s and young people’s settings 1. Understand what is required for competence in own work role 1.1 Describe the duties and responsibilities of own role Assist residents who require help in feeding, dressing, washing, bathing and toileting Help residents with mobility problems and other physical disabilities Help in the use of and care of aids and equipment Care for residents who are sick and Care for residents who are dying Make and change beds, tidy rooms, empty commodes etc, carry out any cleaning tasks that may be allocated by trained staff on duty Assist with simple repairs to residents clothing(if no laundry staff are on duty) and help with laundry as required Set tables and trays, serve meals, clear and tidy dining room Make drinks and prepare light meals / snacks as required Answer emergency bells, give help or summon assistance as required Answer the door & assist visitors Answer the telephone and take accurate messages or call nurse in charge Listen to report and attend and take part in staff meetings Assist in evacuations of residents in the event of a fire, ensure that you are familiar with all fire fighting equipment in the how and are up to date with fire drills Take reasonable care for safety of yourself and other persons at work who may be affected by your acts or omissions at work in accordance with th health &safety at work act 1974 Attend staff training, supervision, appraisal and performance development sessions as required Commit to self appraisal system Enrol for NVQ training when required and commit to the course 1.2 Identify standards that influence the way the role is carried out Code of conduct Regulations Minimum standards National occupational standards 1.3 Describe ways to ensure that personal attitudes and beliefs do not obstruct the quality of work You must not unfairly discriminate against individuals who you support by allowing your personal views to affect your professional relationship with them or the treatment you provide or arrange, for example if an individual who you support is religious and you are not and they express their religious beliefs to you then you cannot say that what they believe is wrong because it is what they believe and their right as an individual. 2. Be able to reflect on own work activities 2.1 Explain why reflecting on work activities is an important way to develop knowledge, skills and practise Reflecting on my own work activities is a good way for me to see where I need to improve my knowledge of certain things I may not fully understand and to see how I

Letter of Intent Personal Statement Example | Topics and Well Written Essays - 250 words

Letter of Intent - Personal Statement Example One of the most meaningful experiences to me was internship in Cairo Microsoft Innovation Center (CMIC). I have also participated in Imagine Cup 09 in Cairo hosted by Microsoft. This experience can serve as a proof of my professional skills and abilities. In my home country, I have worked on autonomous systems development projects, specifically, on Unmanned Aerial Vehicles (UAV) for 15 months. Moreover, I have enough experience in collecting requirements, designing, implementing, and testing different software applications. I also have a good knowledge of some key programming languages, such as, c++, java, and JSP. As a highly motivated person that enjoys working hard and achieving intended results I really want to be the part of this program since it will open a new opportunities towards international work experience. I am grateful in advance for thorough consideration and hope for the call for

Regional Economic Integration (BLOBAL BUSINESS) Essay

Regional Economic Integration (BLOBAL BUSINESS) - Essay Example Custom unions are similar to free trade area, but differ in the idea of treating non-member states. Unlike free trade area where each member nation has the autonomy to decide how to deal with non-member countries, custom unions promote uniform treatment of non-member nations by all member countries. A perfect example of common union is the Gulf Cooperation Council (GCC). Common market on the other hand permits for the development of economically incorporated markets between member nations. It involves the abolition of trade barriers, capital and labour flow limitations and promotes the formation of common trade policies for dealing with non-members. Common Market for Eastern and Southern Africa (COMESA) (Kyambalesa and Houngnikpo 79) is an epitome of common market. Lastly, an economic union refers to an economic agreement formed between countries that involves abolition of trade barriers and implementation of common trade policies, for example the European Union (EU). Regional integration creates trade and employment opportunities for member states and also promotes cooperation between them. However, regional integration may also jeopardize national sovereignty, leads to shift in employment and thwarts diversification in

World Religions Essay Example | Topics and Well Written Essays - 1750 words

World Religions - Essay Example Daoism is a ‘religion’ since it entails an orientation to as well as a relation with the hallowed. Furthermore, Daoism is a ‘tradition’ since it is a society of devoted practitioners linked to one another as a historic as well as energetic continuum (Esposito, Fasching, & Lewis, 2002, p. 498). The Dao is the ultimate or sacred interest of Daoists. There are 4 primary Dao characteristics: a) Source; b) Unnamable mystery; c) All-pervading sacred presence; d) Universe as an astral process (Nature). Additionally, the Dao is ineffable and impersonal. Through an impulsive, neutral procedure, the Dao shifted from primordial un-differentiation-differentiation (the patent realm). Daoists theology, therefore, emphasizes immanence and emanation.The Daoism religion has no founder or standard scripture. Diverse adherents, communities as well as movements worship different scriptures and individuals. Generally speaking, Master Lao (Laozi) receives veneration place, but La ozi is mythological and pseudo-historic. Laozi is a complex figure. In respect to leading scriptures, the ‘Daode Jing’ (the Dao as well as Virtue Scripture), similarly known as (Lao-tzu; ‘the Book of Venerable Masters’), has possibly been most dominant and influential (Esposito, Fasching, & Lewis, 2002). 2. Shinto is Japanese faith that worships all the kami of earth and heaven. Its beginning is as ancient as the Japanese history. Â  Shinto was, therefore, a faith that came into being naturally in Japan. Shintoism is not a religion established and advocated by any particular individual, therefore, there exists no dogma grounded on lessons or actions of the initiator. Shinto has openness to external faiths, even those with an entirely different nature like Buddhism (Esposito, Fasching, & Lewis, 2002). As there is no doctrine, there is no sectionalism. By nature, religions tend to break into several groups because of differences on interpretation of doctrine . In the instance of Shinto there exists no dogmatic dis-confederacy, and this is the reason Shintoism embraces people of dissimilar faiths. Shintoism does not impart that individuals must be liberated from the worldly hardships, a philosophical reflection traditionon life, sufferings and death exist. Shintoism does not satisfy individuals in idealistic terms. However, this is indeed the reason it is calmly acknowledged by many people, without philosophical discrimination (Esposito, Fasching, & Lewis, 2002). Because Shintoism is a faith closely linked to secular-life through celebrations and traditional rites-of-passage, its value organism is closely linked to that of a secular-society. Consequently, though it does not have the sharpness pertaining to logical expansion of thought, Shintoism has instituted its own way over the development of its extensive history. Individuals have been stirred to execute what they think will bring gratification to the ‘Kami’ and to refra in from what could upset Kami (Esposito, Fasching, & Lewis, 2002). 3. Nature in Chinese religion is embraced as a way for man to develop and survive through being in harmony with nature. Nature in the Chinese religion is viewed as basis for all things in the globe and they should be interdependent and inseparable. The Chinese religion opposes the obliteration of the biosphere. It advocates that people must take care of nature, live an environmental life-style that ensures environmental sustainability and protection (Esposito, Fasching, & Lewis, 2002). Chinese religion deems that nature and man are interrelated as well as bound by knots of retribution and reciprocity. If humans are in accord with nature, plus nature is appropriately treated by human-beings, the planet will be harmonious and peaceful, and every single thing

Art To Bring Us Closer To The Truth Philosophy Essay

Art To Bring Us Closer To The Truth Philosophy Essay Art is a lie which brings us closer to the truth- Pablo Picasso Ever since I can remember I have always loved art in one way or another. I remember, on numerous occasions, sitting my father down at the kitchen table and begging him to draw me a family of horses, this consisted of mum and dad and babies running along behind trying to catch up. For a long time I practically worshipped these pictures and let the horses run free in my imagination making them go on big adventures with one another. As I got older the pictures stayed with me, but I grew out of the way they looked. They no longer burst out of the page and came to life; they just did not look like real horses anymore. Life had disappeared from them. I suppose I fell into the trap in which many people fall into. This trap could be called ignorance. Many people believe that skill is the most important feature in a piece of art. They think that paintings or drawings that look-real must be the best because they have required the most attention from the artist. Some people say that these pieces are the true meaning of art. Of course this is something to admire about a piece of work, but does this mean that paintings or drawings with fewer detail are less good? Who is to say that these detailed pictures are the truth? Who is to say what the truth is? In order to put this theory into practice I have taken two pieces of art work. Albrecht Durers Crab made in 1495 and Rembrandt van Rijns Two Studies of a Bird of Paradise. It is obvious how much detail and time Durers watercolour of the Crab has taken but who was to say that the birds are less good and required less skill? Rembrandts Birds do an incredible job of portraying the texture and character of the Birds with merely a few simple lines. He grasps their curiousness and profound features of their faces along with the softness and majestic element of their bodies. The piece may not look as realistic but it portrays the birds characteristics much better, something which could be seen as portraying the true nature of the birds as opposed to a real life drawing. Another example of this are the Disney characters. Mickey Mouse looks nothing like a real mouse but the artist, Walt Disney, knew it would be better to distort or change the way the real thing looked. This could have been to make him seem more like a mouse because of his added characteristics and more pleasurable to watch for a younger audience. By making him less mousy he has made him even more mouse-like. Even though Mickeys appearance is unlike a real mouse at all, a distortion of the truth, you do not see people complaining about it. This is because when watching a film or studying this particular art, people are not worried about art as a work or piece, only a source of entertainment or pleasure. This could also be because Walt Disney is a respected and admired man who is seen as a classical artist whose work has been carried on for generations. Yet, if a modern artist were to draw something in his own personal way, just like Walt Disney once did, he would most likely be frowned upon and thought untalented. This leads us onto another piece. Pablo Picassos work of a hen and her chicks is an interpretation of a mothers caring nature towards her children. They way her body is bent towards them and her soft gaze shows that she is focused entirely on her chicks and their wellbeing. It really is a work that many people would find hard to criticise. However, when Picasso created his piece Cockerel he was not satisfied with giving a life-like aspect to the picture as he had done with the hen and her chicks piece. Instead, he wanted to grasp the birds belligerent and foolish nature. Picasso has taken a cockerel and changed it into something even more chickeny than the real thing. All of the cockerels characteristics are portrayed in the piece so that the onlooker can almost see, touch, hear and feel what the bird would be like in real life. This is where the statement Art is a lie which brings us closer to truth comes into account. The piece Cockerel is a lie because of its distortion of nature, it looks nothing like what a real cockerel looks like. However, it brings us closer to truth, closer to what a real cockerel behaves and acts like by its exaggerated features and comedic charms. In this work we can almost hear exactly what the bird would sound like, when interpreting the piece; one would suggest his voice would be loud, frantic and desperate. This is due to his bulging eyes, elongated neck, his mouth opened to a massive size and his small sharp tongue sticking out. The birds franticness and clumsiness is suggested from his outstretched wings and bowlegge d feet. His toes suggest a thought of scratching around and quick movement showing that he is all over the place. From Picasso portraying the cockerel to be like this, we can see the cockerel to be more like a real cockerel than if Picasso just drew one from life. We humans have a habit suggesting that nature must always look like what is considered, by us, to be normal in paintings. It must always look like what we are used to in our everyday life; we are almost forced from a very young age only to accept plain and predictable shapes and colours as the correct ones. An example of this is how we draw when we are younger. We are led to believe that a tree has one large straight trunk and a round bushy ball of leaves stuck on the top. We all know that no real tree looks like this, but if it were drawn any different, it would be thought unusual. Another example is how children perceive stars. Stars are not star-shaped at all as believed but every child will draw a star like this. This is also when art is a lie which brings us closer to the truth comes into account as well. Even though a star is not shaped like this, it still gives a clear outline that the small star gives off light; the stars hands acting like rays of light being given off. Altho ugh this exaggeration is not necessarily a bad thing, it would be better if everyone disconnected themselves from this trap and we look at things afresh, without interference. In fact, many artists are able to disconnect themselves from this and look at the world and the natural surroundings as if they have never seen them before. This means that they would be seeing everything for the first time. Who is to say that the sky is blue and clouds are white? In fact, we would probably find things in the most astonishing colours and forms. If every person was to think like this and every artist was not persuaded or affected by society, art would never be considered a lie. For me, a lie can be different for each individual person, we as humans have created lies. A lie is seen as something which is not the truth, not normal. Therefore, a piece of art which does not portray the normality of the world is therefore considered a lie. Yet, if there was no such thing as normality, there would never be such thing as a lie. Then we come back to the question; who is to say what the truth is, and what a lie is? I suppose the answer to this question is everyone. We all have different opinions on what is the truth and what is not, but if we all look at things outside of the box and with open eyes, surely we will be able to accept completely different things to what we are used to, to be normal. To conclude, I believe that skill is not the most important aspect in a painting or drawing. If an artist portrays what he or she wants to portray, it cannot be considered a lie. Furthermore, a lie is something which changes according to each individual. Some may believe something to be the truth, while others may believe it is not. No one really knows for sure what is the correct way of drawing or painting a certain object or form. And if they insist that they do and state that people draw it wrongly because it is not like that in normality, it just means that they have been persuaded by society and the people around them, as well as the banality of our own sense perception. An example of this is how children draw hearts in heart-shaped form. Hearts are not really shaped like this at all, but it is how everyone knows a heart to be drawn and is not considered a lie, yet it brings us closer to the truth by showing us that a heart has two sides; a left and a right side. This leads to b iological explanation of what each side does, the right side pumps blood to the lungs to be oxygenised and the left side pumps the oxygenated blood all around the body. The fact that the heart shape shows a left and right side would not be evident if it was just drawn as an oval-like shape. This is how art can bring us closer to the truth even if it is a lie. TOK ESSAY Art is a lie which brings us nearer to the truth (Pablo Picasso). Evaluate this claim in relation to a specific art form (for example visual arts, literature, theatre). Alice Elphinstone Centre number: 002351 Candidate Number: 026 Word Count: 1668

The Eclectic Model Essay -- Education

For my presentation I chose the Eclectic teaching method used in Physical Education. Going into the project I had no idea what the model was or what it involved. I quickly learned the importance of the Eclectic model and how it is the most vital and widely used teaching method out. The reason for this is because it is the combination of all the teaching models and grouping them to the different age levels of the students. Obviously, there are certain games or activities that you would not do with 3rd graders because they are not developed enough to handle them. On the other hand you may not do an activity with high schoolers because they are over developed for it and they will not gain any benefits from it. To better explain how the eclectic model would be used I researched other teaching models and broke them down into 3 categories where they fit best: Elementary, Middle School, and High School. Elementary Physical Education is usually the first time when young children are being professionally taught how to control their bodies and perform basic skills that they will need to succeed in physical activity throughout their lifetime. This is the most important part of a child’s Physical Education because without these skills and abilities they will not be able to exercise properly through life and it could also discourage them from trying different activities. If this happens our country will become even more obese and out of shape. The models we decided fit best in this age group of students were Developmental Education, Tactical Games Model, Movement Model, Interdisciplinary Elementary Education, and Inquiry Model. We discovered that these in particular taught objectives that younger children need before they could move onto m... ...entary school ages as well. When a school district decides to use the eclectic model in their PE program they do it in hopes that the students will apply what they have learned grades K-12 to the rest of their life. As PE teachers it is our job to give students the information needed to live a long, healthy life. When taught correctly, the eclectic model does just that. Works Cited 1. Siedentop, Daryl, Jacqueline Herkowitz, and Judith Rink. Elementary Physical Education Methods. Englewood Cliffs, NJ: Prentice-Hall, 1984. Print. 2. Physical Education for Lifelong Fitness: The Physical Best Teacher's Guide. Leeds: Human Kinetics Europe, 2005. Print. 3. Manimtim-Florescar, Ruth. "Teaching Method: Eclectic | The Manila Bulletin Newspaper Online." The Manila Bulletin Newspaper Online. 27 May 2008. Web. .

Haemochromatosis

In medicine, Iron overload Indicates accumulation of iron In the body from any cause. The most important causes are hereditary haemochromatosis, a genetic disorder. and transfusional Iron overload, which can result from repeated blood transfusion. Terminology Haemochromatosis or haemoslderosls Historically, the term haemochromatosis was initially used to refer to what is now more specifically called haemochromatosis type 1 . Currently, haemochromatosis Is mostly defined as iron overload with a hereditary/primary cause, or originating from a metabolic disorder.However, the term is currently also used more broadly to refer o any form of Iron overload, thus requiring specification of the cause, for example, hereditary haemochromatosis. Hereditary haemochromatosis is an autosomal recessive disorder with estimated prevalence In the population of 1 In 200 among patients with European ancestry, with lower incidence in other ethnic groups. The gene responsible for hereditary haemochromatosis is located on chromosome 6; the majority of hereditary haemochromatosis patients have mutations in this HFE gene.Hereditary haemochromatosis Is characterized by an accelerated rate of Intestinal iron absorption and progressive iron deposition in various tissues that typically egins to be expressed in the third to fifth decades of life, but may occur In children. The most common presentation is hepatic cirrhosis in combination with hypopituitarism, cardiomyopathy, diabetes, arthritis, or hyperpigmentation. Because of the severe sequelae of this disorder if left untreated, and recognizing that treatment is relatively simple, early diagnosis before symptoms or signs appear is Important.In general, the term haemoslderosls Is used to Indicate the pathological effect of iron accumulation in any given organ, which mainly occurs in the form of haemoslderln. Sometimes, the simpler term siderosls Is used Instead. Other definitions distinguishing haemochromatosis or haemosiderosis that are oc casionally used include: Haemosiderosis Is haemochromatosis caused by excessive blood transfusions, that is, haemosiderosis is a form of secondary haemochromatosis.Haemoslderosls is haemoslderln deposition within cells, while haemochromatosis Is haemosiderin within cells and interstitium. Haemosiderosis is iron overload that does not cause tissue damage, while haemochromatosis does. Haemosiderosis Is arbitrarily differentiated from haemochromatosis by the reversible nature of the iron accumulation In the reticuloendothelial system. Clinical presentation Organs commonly affected by haemochromatosis are the liver, heart, and endocrine glands.Haemochromatosis may present with the following clinical syndromes: Cirrhosis of the liver Diabetes due to pancreatic islet cell failure Cardiomyopathy Arthritis Testicular failure Tanning of the skin Joint pain and bone pain 1 OF3 causes The causes can be distinguished between primary cases and less frequent secondary cases . People of Celtic, Br itish, and Scandinavian origin have a particularly high incidence of whom about 10% are carriers of the gene and 1% sufferers from the condition.Primary haemochromatosis The fact that most cases of haemochromatosis were inherited was well known for most of the 20th century, though they were incorrectly assumed to depend on a single gene. The overwhelming majority actually depend on mutations of the HFE gene discovered in 1996, but since then others have been discovered and sometimes are grouped together as â€Å"non-classical hereditary haemochromatosis†, â€Å"non-HFE related hereditary haemochromatosis†, or â€Å"non-HFE haemochromatosis†. Most types of hereditary haemochromatosis have autosomal recessive inheritance, while type 4 has autosomal dominant inheritance.Secondary haemochromatosis Severe chronic haemolysis of any cause, including intravascular haemolysis and ineffective erythropoiesis Multiple frequent blood transfusions, which are usually needed ei ther by individuals with hereditary anaemias or by older patients with severe acquired anaemias such as in myelodysplastic syndromes Excess parenteral iron supplements, such as what can acutely happen in iron poisoning Excess dietary iron Some disorders do not normally cause haemochromatosis on their own, but may do so in the presence of other predisposing factors.These include cirrhosis, teatohepatitis of any cause, porphyria cutanea tarda, prolonged haemodialysis, and post-portacaval shunting. Diagnosis There are several methods available for diagnosing and monitoring iron loading including: Serum ferritin Liver biopsy MRI Serum ferritin is a low-cost, readily available, and minimally invasive method for assessing body iron stores.However, the major problem with using it as an indicator of iron overload is that it can be elevated in a range of other medical conditions unrelated to iron levels including infection, inflammation, fever, liver disease, renal disease, and cancer. Also, total iron binding capacity may be low, but can also be normal. The standard of practice in diagnosis of haemochromatosis was recently reviewed by Pietrangelo. has been extensively validated. More than 11,000 FerriScans have now been conducted in over 120 medical centres across 25 countries.FerriScan is now specifically recommended as a method to measure liver iron concentrations in clinical practice guidelines for thalassaemias, sickle cell disease myelodysplastic syndrome and hereditary haemochromatosis. Family members of those diagnosed with primary haemochromatosis may be advised to be screened genetically to etermine if they are a carrier or if they could develop the disease. This can allow preventative measures to be taken. Prognosis A third of those untreated develop hepatocellular carcinoma.

Data and Computer Communications

DATA AND COMPUTER COMMUNICATIONS Eighth Edition William Stallings Upper Saddle River, New Jersey 07458 Library of Congress Cataloging-in-Publication Data on File Vice President and Editorial Director, ECS: Marcia J. Horton Executive Editor: Tracy Dunkelberger Assistant Editor: Carole Snyder Editorial Assistant: Christianna Lee Executive Managing Editor: Vince O’Brien Managing Editor: Camille Trentacoste Production Editor: Rose Kernan Director of Creative Services: Paul Belfanti Creative Director: Juan Lopez Cover Designer: Bruce Kenselaar Managing Editor,AV Management and Production: Patricia Burns  ©2007 Pearson Education, Inc.Pearson Prentice Hall Pearson Education, Inc. Upper Saddle River, NJ 07458 Art Editor: Gregory Dulles Director, Image Resource Center: Melinda Reo Manager, Rights and Permissions: Zina Arabia Manager,Visual Research: Beth Brenzel Manager, Cover Visual Research and Permissions: Karen Sanatar Manufacturing Manager, ESM: Alexis Heydt-Long Manufacturing B uyer: Lisa McDowell Executive Marketing Manager: Robin O’Brien Marketing Assistant: Mack Patterson All rights reserved. No part of this book may be reproduced in any form or by any means, without permission in writing from the publisher.Pearson Prentice Hallâ„ ¢ is a trademark of Pearson Education, Inc. All other tradmarks or product names are the property of their respective owners. The author and publisher of this book have used their best efforts in preparing this book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation contained in this book. The author and publisher shall not be liable in any event for incidental or consequential amages in connection with, or arising out of, the furnishing, performance, or use of these programs. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 ISBN: 0-13-243310-9 Pearson Education Ltd. , London Pearson Education Australia Pty. Ltd. , Sydney Pearson Education Singapore, Pte. Ltd. Pearson Education North Asia Ltd. , Hong Kong Pearson Education Canada, Inc. , Toronto Pearson Educaci n de Mexico, S. A. de C. V. Pearson Education Japan, Tokyo Pearson Education Malaysia, Pte. Ltd. Pearson Education, Inc. , Upper Saddle River, New Jersey For my scintillating wife ATSWEB SITE FOR DATA AND COMPUTER COMMUNICATIONS, EIGHTH EDITION The Web site at WilliamStallings. com/DCC/DCC8e. html provides support for instructors and students using the book. It includes the following elements. Course Support Materials The course support materials include †¢ Copies of figures from the book in PDF format †¢ A detailed set of course notes in PDF format suitable for student handout or for use as viewgraphs †¢ A set of PowerPoint slides for use as lecture aids †¢ Computer Science Student Support Site: contains a number of links and documents that the student may find useful in his/her ongoing computer science education.The site includes a review of basic, relevant mathematics; advice on research, writing, and doing homework problems; links to computer science research resources, such as report repositories and bibliographies; and other useful links. †¢ An errata sheet for the book, updated at most monthly T DCC Courses The DCC8e Web site includes links to Web sites for courses taught using the book. These sites can provide useful ideas about scheduling and topic ordering, as well as a number of useful handouts and other materials. Useful Web Sites The DCC8e Web site includes links to relevant Web sites, organized by chapter.The links cover a broad spectrum of topics and will enable students to explore timely issues in greater depth. iv WEB SITE FOR DATA AND COMPUTER COMMUNICATIONS, EIGHTH EDITION v Supplemental Documents The DCC8e Web site includes a number of documents that expand on the treatment in the book. Topics include standards organizations, Sockets, TCP/IP checksum, ASCII, and the sampling theorem. Internet Mailing List An Internet mailing list is maintained so that instructors using this book can exchange information, suggestions, and questions with each other and the author.Subscription information is provided at the book’s Web site. Simulation and Modeling Tools The Web site includes links to the cnet Web site and the modeling tools Web site. These packages can be used to analyze and experiment with protocol and network design issues. Each site includes downloadable software and background information. The instructor’s manual includes more information on loading and using the software and suggested student projects. This page intentionally left blank CONTENTS Web Site for Data and Computer Communications Preface xv 1 iv Chapter 0 Reader’s and Instructor’s Guide 0. Outline of the Book 2 0. 2 Roadmap 3 0. 3 Internet and Web Resources 5 0. 4 Standards 6 PART ONE OVERVIEW 9 Chapter 1 Data Communications, Data Networking, and the Internet 10 1. 1 Data Communications and Networking for Today’s Enterprise 12 1. 2 A Communications Model 16 1. 3 Data Communications 19 1. 4 Networks 22 1. 5 The Internet 25 1. 6 An Example Configuration 29 Chapter 2 Protocol Architecture, TCP/IP, and Internet-Based Applications 2. 1 The Need for a Protocol Architecture 33 2. 2 The TCP/IP Protocol Architecture 34 2. 3 The OSI Model 42 2. 4 Standardization within a Protocol Architecture 44 2. Traditional Internet-Based Applications 48 2. 6 Multimedia 48 2. 7 Recommended Reading and Web Sites 53 2. 8 Key Terms, Review Questions, and Problems 54 Appendix 2A The Trivial File Transfer Protocol 57 PART TWO DATA COMMUNICATIONS 62 Chapter 3 Data Transmission 65 3. 1 Concepts and Terminology 67 3. 2 Analog and Digital Data Transmission 78 3. 3 Transmission Impairments 86 3. 4 Channel Capacity 91 3. 5 Recommended Reading and Web Si te 96 3. 6 Key Terms, Review Questions, and Problems Appendix 3A Decibels and Signal Strength 99 Chapter 4 Transmission Media 102 4. Guided Transmission Media 104 4. 2 Wireless Transmission 117 4. 3 Wireless Propagation 125 32 96 vii viii CONTENTS 4. 4 4. 5 4. 6 Line-of-Sight Transmission 129 Recommended Reading and Web Sites 133 Key Terms, Review Questions, and Problems 134 Chapter 5 Signal Encoding Techniques 138 5. 1 Digital Data, Digital Signals 141 5. 2 Digital Data, Analog Signals 151 5. 3 Analog Data, Digital Signals 162 5. 4 Analog Data, Analog Signals 168 5. 5 Recommended Reading 175 5. 6 Key Terms, Review Questions, and Problems 175 Chapter 6 Digital Data Communication Techniques 180 6. Asynchronous and Synchronous Transmission 182 6. 2 Types of Errors 186 6. 3 Error Detection 186 6. 4 Error Correction 196 6. 5 Line Configurations 201 6. 6 Recommended Reading 203 6. 7 Key Terms, Review Questions, and Problems 204 Chapter 7 Data Link Control Protocols 207 7. 1 Flow Control 209 7. 2 Error Control 216 7. 3 High-Level Data Link Control (HDLC) 222 7. 4 Recommended Reading 228 7. 5 Key Terms, Review Questions, and Problems 229 Appendix 7A Performance Issues 232 Chapter 8 Multiplexing 239 8. 1 Frequency-Division Multiplexing 242 8. 2 Synchronous Time-Division Multiplexing 248 8. Statistical Time-Division Multiplexing 258 8. 4 Asymmetric Digital Subscriber Line 265 8. 5 xDSL 268 8. 6 Recommended Reading and Web Sites 269 8. 7 Key Terms, Review Questions, and Problems 270 Chapter 9 Spread Spectrum 274 9. 1 The Concept of Spread Spectrum 276 9. 2 Frequency Hopping Spread Spectrum 277 9. 3 Direct Sequence Spread Spectrum 282 9. 4 Code-Division Multiple Access 287 9. 5 Recommended Reading and Web Site 290 9. 6 Key Terms, Review Questions, and Problems 291 CONTENTS ix PART THREE WIDE AREA NETWORKS 295 Chapter 10 Circuit Switching and Packet Switching 297 10. Switched Communications Networks 299 10. 2 Circuit Switching Networks 301 10. 3 Circuit Switching Concepts 304 10. 4 Softswitch Architecture 307 10. 5 Packet-Switching Principles 309 10. 6 X. 25 317 10. 7 Frame Relay 319 10. 8 Recommended Reading and Web Sites 324 10. 9 Key Terms, Review Questions, and Problems 325 Chapter 11 Asynchronous Transfer Mode 328 11. 1 Protocol Architecture 329 11. 2 ATM Logical Connections 331 11. 3 ATM Cells 335 11. 4 Transmission of ATM Cells 340 11. 5 ATM Service Categories 345 11. 6 Recommended Reading and Web Sites 348 11. Key Terms, Review Questions, and Problems 349 Chapter 12 Routing in Switched Networks 351 12. 1 Routing in Packet-Switching Networks 352 12. 2 Examples: Routing in ARPANET 362 12. 3 Least-Cost Algorithms 367 12. 4 Recommended Reading 372 12. 5 Key Terms, Review Questions, and Problems 373 Chapter 13 Congestion Control in Data Networks 377 13. 1 Effects of Congestion 379 13. 2 Congestion Control 383 13. 3 Traffic Management 386 13. 4 Congestion Control in Packet-Switching Networks 13. 5 Frame Relay Congestion Control 388 13. 6 ATM Traff ic Management 394 13. 7 ATM-GFR Traffic Management 406 13. Recommended Reading 409 13. 9 Key Terms, Review Questions, and Problems 410 Chapter 14 Cellular Wireless Networks 413 14. 1 Principles of Cellular Networks 415 14. 2 First Generation Analog 427 14. 3 Second Generation CDMA 429 14. 4 Third Generation Systems 437 14. 5 Recommended Reading and Web Sites 440 14. 6 Key Terms, Review Questions, and Problems 441 387 x CONTENTS PART FOUR LOCAL AREA NETWORKS 444 Chapter 15 Local Area Network Overview 446 15. 1 Background 448 15. 2 Topologies and Transmission Media 451 15. 3 LAN Protocol Architecture 457 15. 4 Bridges 465 15. 5 Layer 2 and Layer 3 Switches 473 15. Recommended Reading and Web Site 478 15. 7 Key Terms, Review Questions, and Problems 479 Chapter 16 High-Speed LANs 482 16. 1 The Emergence of High-Speed LANs 483 16. 2 Ethernet 485 16. 3 Fibre Channel 500 16. 4 Recommended Reading and Web Sites 504 16. 5 Key Terms, Review Questions, and Problems 506 Appendix 16A Digital Sig nal Encoding for LANs 508 Appendix 16B Performance Issues 514 Appendix 16C Scrambling 518 Chapter 17 Wireless LANs 522 17. 1 Overview 523 17. 2 Wireless LAN Technology 528 17. 3 IEEE 802. 11 Architecture and Services 531 17. 4 IEEE 802. 11 Medium Access Control 535 17. 5 IEEE 802. 1Physical Layer 543 17. 6 IEEE 802. 11 Security Considerations 549 Recommended Reading and Web Sites 550 17. 7 17. 8 Key Terms, Review Questions, and Problems 551 PART FIVE INTERNET AND TRANSPORT PROTOCOLS Chapter 18 Internetwork Protocols 556 18. 1 Basic Protocol Functions 558 18. 2 Principles of Internetworking 566 18. 3 Internet Protocol Operation 569 18. 4 Internet Protocol 576 18. 5 IPv6 586 18. 6 Virtual Private Networks and IP Security 596 18. 7 Recommended Reading and Web Sites 599 18. 8 Key Terms, Review Questions, and Problems 600 Chapter 19 Internetwork Operation 603 19. 1 Multicasting 605 19. Routing Protocols 614 19. 3 Integrated Services Architecture 625 19. 4 Differentiated Services 636 554 CONTENTS xi 19. 5 19. 6 19. 7 19. 8 Service Level Agreements 645 IP Performance Metrics 646 Recommended Reading and Web Sites 649 Key Terms, Review Questions, and Problems 651 657 Chapter 20 Transport Protocols 655 20. 1 Connection-Oriented Transport Protocol Mechanisms 20. 2 TCP 674 20. 3 TCP Congestion Control 683 20. 4 UDP 693 20. 5 Recommended Reading and Web Sites 695 Key Terms, Review Questions, and Problems 695 20. 6 PART SIX Chapter 21 21. 1 21. 2 21. 3 21. 4 21. 5 21. 6 21. 7 21. 8 21. INTERNET APPLICATIONS 699 Network Security 701 Security Requirements and Attacks 703 Confidentiality with Conventional Encryption 705 Message Authentication and Hash Functions 713 Public-Key Encryption and Digital Signatures 720 Secure Socket Layer and Transport Layer Security 727 IPv4 and IPv6 Security 732 Wi-Fi Protected Access 737 Recommended Reading and Web Sites 739 Key Terms, Review Questions, and Problems 740 Chapter 22 Internet Applications—Electronic Mail and Network Managemen t 22. 1 Electronic Mail: SMTP and MIME 745 22. 2 Network Management: SNMP 760 22. 3 Recommended Reading and Web Sites 770 22. Key Terms, Review Questions, and Problems 771 743 Chapter 23 Internet Applications—Internet Directory Service and World Wide Web 23. 1 Internet Directory Service: DNS 774 23. 2 Web Access: HTTP 784 23. 3 Recommended Reading and Web Sites 795 23. 4 Key Terms, Review Questions, and Problems 796 Chapter 24 Internet Applications—Multimedia 799 24. 1 Audio and Video Compression 800 24. 2 Real-Time Traffic 808 24. 3 Voice Over IP and Multimedia Support—SIP 811 24. 4 Real-Time Transport Protocol (RTP) 820 24. 5 Recommended Reading and Web Sites 831 24. 6 Key Terms, Review Questions, and Problems 832 773 ii CONTENTS APPENDICES 835 Appendix A Fourier Analysis 835 A. 1 Fourier Series Representation of Periodic Signals 836 A. 2 Fourier Transform Representation of Aperiodic Signals 837 A. 3 Recommended Reading 840 Appendix B Projects for Teaching Dat a and Computer Communications B. 1 Practical Exercises 842 B. 2 Sockets Projects 843 B. 3 Ethereal Projects 843 B. 4 Simulation and Modeling Projects 844 B. 5 Performance Modeling 844 B. 6 Research Projects 845 B. 7 Reading/Report Assignments 845 B. 8 Writing Assignments 845 B. 9 Discussion Topics 846 References Index 858 ONLINE APPENDICES WilliamStallings. om/DCC Appendix C Sockets: A Programmer’s Introduction C. 1 Versions of Sockets C. 2 Sockets, Socket Descriptors, Ports, and Connections The Client/Server Model of Communication C. 3 C. 4 Sockets Elements C. 5 Stream and Datagram Sockets C. 6 Run-Time Program Control C. 7 Remote Execution of a Windows Console Application Appendix D Standards Organizations D. 1 The Importance of Standards D. 2 Standards and Regulation D. 3 Standards-Setting Organizations Appendix E Appendix F The International Reference Alphabet Proof of the Sampling Theorem 847 841 Appendix G Physical-Layer Interfacing G. 1 V. 24/EIA-232-F G. ISDN Physical Interface Appendix H The OSI Model H. 1 The Model H. 2 The OSI Layers CONTENTS xiii Appendix I Queuing Effects I. 1 Queuing Models I. 2 Queuing Results Appendix J Orthogonality, Correlation, and Autocorrelation J. 1 Correlation and Autocorrelation J. 2 Orthogonal Codes Appendix K The TCP/IP Checksum K. 1 Ones-Complement Addition K. 2 Use in TCP and IP Appendix L TCP/IP Example Appendix M Uniform Resource Locators (URLs) and Uniform Resource Identifiers (URIs) M. 1 Uniform Resource Locator M. 2 Uniform Resource Identifier M. 3 To Learn More Appendix N Glossary Augmented Backus-Naur FormThis page intentionally left blank PREFACE Begin at the beginning and go on till you come to the end; then stop. —Alice in Wonderland, Lewis Carroll OBJECTIVES This book attempts to provide a unified overview of the broad field of data and computer communications. The organization of the book reflects an attempt to break this massive subject into comprehensible parts and to build, piece by piec e, a survey of the state of the art. The book emphasizes basic principles and topics of fundamental importance concerning the technology and architecture of this field and provides a detailed discussion of leading-edge topics.The following basic themes serve to unify the discussion: †¢ Principles: Although the scope of this book is broad, there are a number of basic principles that appear repeatedly as themes and that unify this field. Examples are multiplexing, flow control, and error control. The book highlights these principles and contrasts their application in specific areas of technology. †¢ Design approaches: The book examines alternative approaches to meeting specific communication requirements. †¢ Standards: Standards have come to assume an increasingly important, indeed dominant, role in this field.An understanding of the current status and future direction of technology requires a comprehensive discussion of the related standards. INTENDED AUDIENCE The book is intended for both an academic and a professional audience. For the professional interested in this field, the book serves as a basic reference volume and is suitable for self-study. As a textbook, it can be used for a one-semester or two-semester course. It covers the material in Networking (NET), a core area in the Information Technology body of knowledge, which is part of the Draft ACM/IEEE/AIS Computing Curricula 2005.The book also covers the material in Computer Networks (CE-NWK), a core area in Computer Engineering 2004 Curriculum Guidelines from the ACM/IEEE Joint Task Force on Computing Curricula. PLAN OF THE TEXT The book is divided into six parts (see Chapter 0): †¢ Overview †¢ Data Communications †¢ Wide Area Networks xv xvi PREFACE †¢ Local Area Networks †¢ Internet and Transport Protocols †¢ Internet Applications In addition, the book includes an extensive glossary, a list of frequently used acronyms, and a bibliography. Each chapter inc ludes problems and suggestions for further reading.The chapters and parts of the book are sufficiently modular to provide a great deal of flexibility in the design of courses. See Chapter 0 for a number of detailed suggestions for both top-down and bottom-up course strategies. INSTRUCTIONAL SUPPORT MATERIALS To support instructors, the following materials are provided: †¢ Solutions Manual: Solutions to all end-of-chapter Review Questions and Problems. †¢ PowerPoint Slides: A set of slides covering all chapters, suitable for use in lecturing. †¢ PDF files: Reproductions of all figures and tables from the book. Projects Manual: Suggested project assignments for all of the project categories listed below. Instructors may contact their Pearson Education or Prentice Hall representative for access to these materials. In addition, the book’s Web site supports instructors with: †¢ Links to Webs sites for other courses being taught using this book †¢ Sign up i nformation for an Internet mailing list for instructors INTERNET SERVICES FOR INSTRUCTORS AND STUDENTS There is a Web site for this book that provides support for students and instructors.The site includes links to other relevant sites, transparency masters of figures in the book, and sign-up information for the book’s Internet mailing list. The Web page is at WilliamStallings. com/DCC/DCC8e. html; see the section, Web Site for Data and Computer Communications, preceding the Table of Contents, for more information. An Internet mailing list has been set up so that instructors using this book can exchange information, suggestions, and questions with each other and with the author. As soon as typos or other errors are discovered, an errata list for this book will be available at WilliamStallings. om. PROJECTS AND OTHER STUDENT EXERCISES For many instructors, an important component of a data communications or networking course is a project or set of projects by which the student gets hands-on experience to reinforce concepts from the text. This book provides an unparalleled degree of support for including a projects component in the course. The instructor’s supplement not only includes guidance on how to assign and structure the projects but also includes a set of User’s PREFACE xvii Manuals for various project types plus specific assignments, all written especially for this book.Instructors can assign work in the following areas: †¢ Practical exercises: Using network commands, the student gains experience in network connectivity. †¢ Sockets programming projects: The book is supported by a detailed description of Sockets available at the book’s Web site. The Instructors supplement includes a set of programming projects. Sockets programming is an â€Å"easy† topic and one that can result in very satisfying hands-on projects for students. †¢ Ethereal projects: Ethereal is a protocol analyzer that enables students to study the behavior of protocols. Simulation projects: The student can use the simulation package cnet to analyze network behavior. †¢ Performance modeling projects: Two performance modeling techniques are provided a tools package and OPNET. †¢ Research projects: The instructor’s supplement includes a list of suggested research projects that would involve Web and literature searches. †¢ Reading/report assignments: The instructor’s supplement includes a list of papers that can be assigned for reading and writing a report, plus suggested assignment wording. Writing assignments: The instructor’s supplement includes a list of writing assignments to facilitate learning the material. †¢ Discussion topics: These topics can be used in a classroom, chat room, or message board environment to explore certain areas in greater depth and to foster student collaboration. This diverse set of projects and other student exercises enables the instructor to use t he book as one component in a rich and varied learning experience and to tailor a course plan to meet the specific needs of the instructor and students. See Appendix B for details.WHAT’S NEW IN THE EIGHTH EDITION This eighth edition is seeing the light of day less than four years after the publication of the seventh edition. During that time, the pace of change in this field continues unabated. In this new edition, I try to capture these changes while maintaining a broad and comprehensive coverage of the entire field. To begin the process of revision, the seventh edition of this book was extensively reviewed by a number of professors who teach the subject. The result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved.Also, a number of new â€Å"field-tested† problems have been added. Beyond these refinements to improve pedagogy and user friendliness, there have been major substantive changes throughout the book . Every chapter has been revised, new chapters have been added, and the overall organization of the book has changed. Highlights include: †¢ Updated coverage of Gigabit Ethernet and 10-Gbps Ethernet: New details of these standards are provided. †¢ Updated coverage of WiFi/IEEE 802. 11 wireless LANs: IEEE 802. 11 and the related WiFi specifications have continued to evolve. viii PREFACE †¢ New coverage of IP performance metrics and service level agreements (SLAs): These aspects of Quality of Service (QoS) and performance monitoring are increasingly important. †¢ Address Resolution Protocol (ARP): This important protocol is now covered. †¢ New coverage of TCP Tahoe, Reno, and NewReno: These congestion control algorithms are now common in most commercial implementations. †¢ Expanded coverage of security: Chapter 21 is more detailed; other chapters provide overview of security for the relevant topic.Among the new topics are Wi-Fi Protected Access (WPA) and the secure hash algorithm SHA-512. †¢ Domain Name System (DNS): This important scheme is now covered. †¢ New coverage of multimedia: Introductory section in Chapter 2; detailed coverage in Chapter 24. Topics covered include video compression, SIP, and RTP. †¢ Online appendices: Fourteen online appendices provide additional detail on important topics in the text, including Sockets programming, queuing models, the Internet checksum, a detailed example of TCP/IP operation, and the BNF grammar.In addition, throughout the book, virtually every topic has been updated to reflect the developments in standards and technology that have occurred since the publication of the seventh edition. ACKNOWLEDGMENTS This new edition has benefited from review by a number of people, who gave generously of their time and expertise. The following people reviewed all or a large part of the manuscript: Xin Liu- (UC, Davis), Jorge Cobb, Andras Farago, Dr. Prasant Mohapatra (UC Davis), Dr. Jingxi an Wu (Sonoma State University), G. R.Dattareya (UT Dallas), Guanling Chen (Umass, Lowell), Bob Roohaprvar (Cal State East Bay), Ahmed Banafa (Cal State East Bay), Ching-Chen Lee (CSU Hayward), and Daji Qaio (Iowa State). Thanks also to the many people who provided detailed technical reviews of a single chapter: Dave Tweed, Bruce Lane, Denis McMahon, Charles Freund, Paul Hoadley, Stephen Ma, Sandeep Subramaniam, Dragan Cvetkovic, Fernando Gont, Neil Giles, Rajesh Thundil, and Rick Jones. In addition, Larry Owens of California State University and Katia Obraczka of the University of Southern California provided some homework problems.Thanks also to the following contributors. Zornitza Prodanoff of the University of North Florida prepared the appendix on Sockets programming. Michael Harris of the University of South Florida is responsible for the Ethereal exercises and user’s guide. Lawrie Brown of the Australian Defence Force Academy of the University of New South Wales produc ed the PPT lecture slides. Finally, I would like to thank the many people responsible for the publication of the book, all of whom did their usual excellent job.This includes the staff at Prentice Hall, particularly my editor Tracy Dunkelberger, her assistants Christianna Lee and Carole Snyder, and production manager Rose Kernan. Also, Patricia M. Daly did the copy editing. CHAPTER READER’S AND INSTRUCTOR’S GUIDE 0. 1 0. 2 0. 3 0. 4 Outline of the Book Roadmap Internet and Web Resources Standards 0 1 2 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE â€Å"In the meanwhile, then,† demanded Li-loe, â€Å"relate to me the story to which reference has been made, thereby proving the truth of your assertion, and at the same time affording n entertainment of a somewhat exceptional kind. † â€Å"The shadows lengthen,† replied Kai Lung, â€Å"but as the narrative in question is of an inconspicuous span I will raise no barrier against your flatter ing request, especially as it indicates an awakening taste hitherto unexpected. † —Kai Lung’s Golden Hours, Earnest Bramah This book, with its accompanying Web site, covers a lot of material. Here we give the reader some basic background information. 0. 1 OUTLINE OF THE BOOK The book is organized into five parts: Part One. Overview: Provides an introduction to the range of topics covered in the book.This part includes a general overview of data communications and networking and a discussion of protocols, OSI, and the TCP/IP protocol suite. Part Two. Data Communications: Concerned primarily with the exchange of data between two directly connected devices. Within this restricted scope, the key aspects of transmission, interfacing, link control, and multiplexing are examined. Part Three. Wide Area Networks: Examines the internal mechanisms and user-network interfaces that have been developed to support voice, data, and multimedia communications over long-distance ne tworks.The traditional technologies of packet switching and circuit switching are examined, as well as the more recent ATM and wireless WANs. Separate chapters are devoted to routing and congestion control issues that are relevant both to switched data networks and to the Internet. Part Four. Local Area Networks: Explores the technologies and architectures that have been developed for networking over shorter distances. The transmission media, topologies, and medium access control protocols that are the key ingredients of a LAN design are explored and specific standardized LAN systems examined.Part Five. Networking Protocols: Explores both the architectural principles and the mechanisms required for the exchange of data among computers, workstations, servers, and other data processing devices. Much of the material in this part relates to the TCP/IP protocol suite. Part Six. Internet Applications: Looks at a range of applications that operate over the Internet. A more detailed, chapte r-by-chapter summary of each part appears at the beginning of that part. 0. 2 / ROADMAP 3 0. 2 ROADMAP Course EmphasisThe material in this book is organized into four broad categories: data transmission and communication; communications networks; network protocols; and applications and security. The chapters and parts of the book are sufficiently modular to provide a great deal of flexibility in the design of courses. The following are suggestions for three different course designs: †¢ Fundamentals of Data Communications: Parts One (overview) and Two (data communications) and Chapters 10 and 11 (circuit switching, packet switching, and ATM). Communications Networks: If the student has a basic background in data communications, then this course could cover Parts One (overview), Three (WAN), and Four (LAN). †¢ Computer Networks: If the student has a basic background in data communications, then this course could cover Part One (overview), Chapters 6 and 7 (data communication techniques and data link control), Part Five (protocols), and part or all of Part Six (applications). In addition, a more streamlined course that covers the entire book is possible by eliminating certain chapters that are not essential on a first reading.Chapters that could be optional are Chapters 3 (data transmission) and 4 (transmission media), if the student has a basic understanding of these topics; Chapter 8 (multiplexing); Chapter 9 (spread spectrum); Chapters 12 through 14 (routing, congestion control, cellular networks); Chapter 18 (internetworking); and Chapter 21 (network security). Bottom-Up versus Top-Down The book is organized in a modular fashion. After reading Part One, the other parts can be read in a number of possible sequences.Figure 0. 1a shows the bottom-up approach provided by reading the book from front to back. With this approach, each part builds on the material in the previous part, so that it is always clear how a given layer of functionality is supporte d from below. There is more material than can be comfortably covered in a single semester, but the book’s organization makes it easy to eliminate some chapters and maintain the bottom-up sequence. Figure 0. 1b suggests one approach to a survey course.Some readers, and some instructors, are more comfortable with a top-down approach. After the background material (Part One), the reader continues at the application level and works down through the protocol layers. This has the advantage of immediately focusing on the most visible part of the material, the applications, and then seeing, progressively, how each layer is supported by the next layer down. Figure 0. 1c is an example of a comprehensive treatment and Figure 0. 1d is an example of a survey treatment. 4 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDEPart One Overview Part Two Data Communications Part Three Wide Area Networks Part Four Local Area Networks Part Five Internet and Transport Protocols Part Six Inter net Applications (a) A bottom-up approach Part One Overview Chapter 18 The Internet Protocol Part Six Internet Applications Part Five TCP/IP Part Three WANs Part Four LANs Part Two Data Communications (c) A top-down approach (d) Another top-down approach (b) Another bottom-up approach Part One Overview Chapter 18 The Internet Protocol Part Six Internet Applications Part Five TCP/IP Part Three WANs (10, 12) Part Four LANs (15) Part One Overview (1, 2) Part Two Data Communications (3, 6, 7, 8) Part Three WANs (10, 12) Part Four LANs (15) Part Five TCP/IP (18, 20) Figure 0. 1 Suggested Reading Orders Finally, it is possible to select chapters to reflect specific teaching objectives by not sticking to a strict chapter ordering. We give two examples used in courses taught with the seventh edition.One course used the sequence Part One (Overview); Chapter 3 (Data Transmission); Chapter 6 (Digital Data Communications Techniques); Chapter 7 (Data Link Control); Chapter 15 (LAN Overview); Cha pter 16 (High-Speed LANs); Chapter 10 (Circuit and Packet Switching); Chapter 12 (Routing); Chapter 18 (Internet Protocols); and Chapter 19 (Internet Operation). The other course used the sequence Part One (Overview); Chapter 3 (Data Transmission); Chapter 4 (Guided and Wireless Transmission); Chapter 5 (Signal Encoding Techniques); Chapter 8 (Multiplexing); Chapter 15 (LAN 0. 3 / INTERNET AND WEB RESOURCES 5 Overview); Chapter 16 (High-Speed LANs); Chapter 10 (Circuit and Packet Switching); Chapter 20 (Transport Protocols); Chapter 18 (Internet Protocols); and Chapter 19 (Internet Operation). 0. 3 INTERNET AND WEB RESOURCES There are a number of resources available on the Internet and the Web to support this book and to help one keep up with developments in this field.Web Sites for This Book A special Web page has been set up for this book at WilliamStallings. com/DCC/ DCC8e. html. See the two-page layout at the beginning of this book for a detailed description of that site. As soo n as any typos or other errors are discovered, an errata list for this book will be available at the Web site. Please report any errors that you spot. Errata sheets for my other books are at WilliamStallings. com. I also maintain the Computer Science Student Resource Site, at WilliamStallings. com/StudentSupport. html. The purpose of this site is to provide documents, information, and links for computer science students and professionals.Links and documents are organized into four categories: †¢ Math: Includes a basic math refresher, a queuing analysis primer, a number system primer, and links to numerous math sites †¢ How-to: Advice and guidance for solving homework problems, writing technical reports, and preparing technical presentations †¢ Research resources: Links to important collections of papers, technical reports, and bibliographies †¢ Miscellaneous: A variety of useful documents and links Other Web Sites There are numerous Web sites that provide informa tion related to the topics of this book. In subsequent chapters, pointers to specific Web sites can be found in the Recommended Reading and Web Sites section. Because the addresses for Web sites tend to change frequently, I have not included URLs in the book. For all of the Web sites listed in the book, the appropriate link can be found at this book’s Web site. Other links not mentioned in this book will be added to the Web site over time.The following are Web sites of general interest related to data and computer communications: †¢ Network World: Information and links to resources about data communications and networking. †¢ IETF: Maintains archives that relate to the Internet and IETF activities. Includes keyword-indexed library of RFCs and draft documents as well as many other documents related to the Internet and related protocols. 6 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE †¢ Vendors: Links to thousands of hardware and software vendors who currently have Web sites, as well as a list of thousands of computer and networking companies in a phone directory. †¢ IEEE Communications Society: Good way to keep up on conferences, publications, and so on. ACM Special Interest Group on Communications (SIGCOMM): Good way to keep up on conferences, publications, and so on. †¢ International Telecommunications Union: Contains a listing of ITU-T recommendations, plus information on obtaining ITU-T documents in hard copy or on DVD. †¢ International Organization for Standardization: Contains a listing of ISO standards, plus information on obtaining ISO documents in hard copy or on CD-ROM. †¢ CommWeb: Links to vendors, tutorials, and other useful information. †¢ CommsDesign: Lot of useful articles, tutorials, and product information. A bit hard to navigate, but worthwhile. USENET Newsgroups A number of USENET newsgroups are devoted to some aspect of data communications, networks, and protocols.As with virtually all USENET groups, there is a high noise-to-signal ratio, but it is worth experimenting to see if any meet your needs. The most relevant are as follows: †¢ comp. dcom. lans, comp. dcom. lans. misc: General discussions of LANs †¢ comp. dcom. lans. ethernet: Covers Ethernet, Ethernet-like systems, and the IEEE 802. 3 CSMA/CD standards †¢ comp. std. wireless: General discussion of wireless networks, including wireless LANs †¢ comp. security. misc: Computer security and encryption †¢ comp. dcom. cell-relay: Covers ATM and ATM LANs †¢ comp. dcom. frame-relay: Covers frame relay networks †¢ comp. dcom. net-management: Discussion of network management applications, protocols, and standards †¢ comp. rotocols. tcp-ip: The TCP/IP protocol suite 0. 4 STANDARDS It has long been accepted in the telecommunications industry that standards are required to govern the physical, electrical, and procedural characteristics of communication equipment. In the past, this view has not been embraced by the computer industry. Whereas communication equipment vendors recognize that their 0. 4 / STANDARDS 7 equipment will generally interface to and communicate with other vendors’ equipment, computer vendors have traditionally attempted to monopolize their customers. The proliferation of computers and distributed processing has made that an untenable position.Computers from different vendors must communicate with each other and, with the ongoing evolution of protocol standards, customers will no longer accept special-purpose protocol conversion software development. The result is that standards now permeate all of the areas of technology discussed in this book. There are a number of advantages and disadvantages to the standards-making process. We list here the most striking ones. The principal advantages of standards are as follows: †¢ A standard assures that there will be a large market for a particular piece of equipment or software. Thi s encourages mass production and, in some cases, the use of large-scale-integration (LSI) or very-large-scale-integration (VLSI) techniques, resulting in lower costs. A standard allows products from multiple vendors to communicate, giving the purchaser more flexibility in equipment selection and use. The principal disadvantages are as follows: †¢ A standard tends to freeze the technology. By the time a standard is developed, subjected to review and compromise, and promulgated, more efficient techniques are possible. †¢ There are multiple standards for the same thing. This is not a disadvantage of standards per se, but of the current way things are done. Fortunately, in recent years the various standards-making organizations have begun to cooperate more closely. Nevertheless, there are still areas where multiple conflicting standards exist.Throughout this book, we describe the most important standards in use or being developed for various aspects of data and computer commun ications. Various organizations have been involved in the development or promotion of these standards. The following are the most important (in the current context) of these organizations: †¢ Internet Society: The Internet SOCiety (ISOC) is a professional membership society with more than 150 organizational and 6000 individual members in over 100 countries. It provides leadership in addressing issues that confront the future of the Internet and is the organization home for the groups responsible for Internet infrastructure standards, including the Internet Engineering Task Force (IETF) and the Internet Architecture Board (IAB).All of the RFCs and Internet standards are developed through these organizations. †¢ IEEE 802: The IEEE (Institute of Electrical and Electronics Engineers) 802 LAN/MAN Standards Committee develops local area network standards and metropolitan area network standards. The most widely used standards are for the Ethernet family, wireless LAN, bridging, a nd virtual bridged LANs. An individual working group provides the focus for each area. 8 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE †¢ ITU-T: The International Telecommunication Union (ITU) is an international organization within the United Nations System where governments and the private sector coordinate global telecom networks and services.The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors of the ITU. ITU-T’s mission is the production of standards covering all fields of telecommunications. †¢ ATM Forum: The ATM Forum is an international nonprofit organization formed with the objective of accelerating the use of ATM (asynchronous transfer mode) products and services through a rapid convergence of interoperability specifications. In addition, the Forum promotes industry cooperation and awareness. †¢ ISO: The International Organization for Standardization (ISO)1 is a worldwide federation of national standards bod ies from more than 140 countries, one from each country.ISO is a nongovernmental organization that promotes the development of standardization and related activities with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological, and economic activity. ISO’s work results in international agreements that are published as International Standards. A more detailed discussion of these organizations is contained in Appendix D. 1 ISO is not an acronym (in which case it would be IOS), but a word, derived from the Greek, meaning equal. PART ONE Overview The purpose of Part One is to provide a background and context for the remainder of this book. The broad range of topics that are encompassed in the field of data and computer communications is introduced, and the fundamental concepts of protocols and protocol architectures are examined.ROAD MAP FOR PART ONE Chapter 1 Data Communicati ons, Data Networks, and The Internet Chapter 1 provides an overview of Parts Two through Four of the book, giving the â€Å"big picture. † In essence, the book deals with four topics: data communications over a transmission link; wide area networks; local area networks; and protocols and the TCP/IP protocol architecture. Chapter 1 provides a preview of the first three of these topics. Chapter 2 Protocol Architecture, TCP/IP, and Internet-Based Applications Chapter 2 discusses the concept protocol architectures. This chapter can be read immediately following Chapter 1 or deferred until the beginning of Part Three, Four, or Five.After a general introduction, the chapter deals with the two most important protocol architectures: the Open Systems Interconnection (OSI) model and TCP/IP. Although the OSI model is often used as the framework for discourse in this area, it is the TCP/IP protocol suite that is the basis for most commercially available interoperable products and that is the focus of Parts Five and Six of this book. 9 CHAPTER DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 Data Communications and Networking for Today’s Enterprise A Communications Model Data Communications Networks The Internet An Example Configuration 1 10 The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. The Mathematical Theory of Communication, Claude Shannon KEY POINTS †¢ The scope of this book is broad, covering three general areas: data communications, networking, and protocols; the first two are introduced in this chapter. Data communications deals with the transmission of signals in a reliable and efficient manner. Topics covered include signal transmission, transmission media, signal encoding, interfacing, data link control, and multiplexing. Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices. This field is generally divided into the topics of local area networks (LANs) and wide area networks (WANs). †¢ †¢The 1970s and 1980s saw a merger of the fields of computer science and data communications that profoundly changed the technology, products, and companies of the now combined computer-communications industry. The computercommunications revolution has produced several remarkable facts: †¢ There is no fundamental difference between data processing (computers) and data communications (transmission and switching equipment). †¢ There are no fundamental differences among data, voice, and video communications. †¢ The distinction among single-processor computer, multiprocessor computer, local network, metropolitan network, and long-haul network has blurred.One effect of these trends has been a growing overlap of the computer and communications industries, from component fabrication to system integration. Another resul t is the development of integrated systems that transmit and process all types of data and information. Both the technology and the technical standards organizations are driving toward integrated public systems that make virtually all data and information sources around the world easily and uniformly accessible. This book aims to provide a unified view of the broad field of data and computer communications. The organization of the book reflects an attempt to break this massive subject into comprehensible parts and to build, piece by piece, a survey of the state of the art.This introductory chapter begins with a general model of communications. Then a brief discussion introduces each of the Parts Two through Four of this book. Chapter 2 provides an overview to Parts Five and Six 11 12 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET 1. 1 DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE Effective and efficient data communication and networking facilitie s are vital to any enterprise. In this section, we first look at trends that are increasing the challenge for the business manager in planning and managing such facilities. Then we look specifically at the requirement for ever-greater transmission speeds and network capacity. TrendsThree different forces have consistently driven the architecture and evolution of data communications and networking facilities: traffic growth, development of new services, and advances in technology. Communication traffic, both local (within a building or building complex) and long distance, both voice and data, has been growing at a high and steady rate for decades. The increasing emphasis on office automation, remote access, online transactions, and other productivity measures means that this trend is likely to continue. Thus, managers are constantly struggling to maximize capacity and minimize transmission costs. As businesses rely more and more on information technology, the range of services expand s. This increases the demand for high-capacity networking and transmission facilities.In turn, the continuing growth in high-speed network offerings with the continuing drop in prices encourages the expansion of services. Thus, growth in services and growth in traffic capacity go hand in hand. Figure 1. 1 gives some examples of information-based services and the data rates needed to support them [ELSA02]. Finally, trends in technology enable the provision of increasing traffic capacity and the support of a wide range of services. Four technology trends are particularly notable: 1. The trend toward faster and cheaper, both in computing and communications, continues. In terms of computing, this means more powerful computers and clusters of computers capable of supporting more demanding applications, such as multimedia applications.In terms of communications, the increasing use of optical fiber has brought transmission prices down and greatly increased capacity. For example, for long-d istance telecommunication and data network links, recent offerings of dense wavelength division multiplexing (DWDM) enable capacities of many terabits per second. For local area networks (LANs) many enterprises now have Gigabit Ethernet backbone networks and some are beginning to deploy 10-Gbps Ethernet. 2. Both voice-oriented telecommunications networks, such as the public switched telephone network (PSTN), and data networks, including the Internet, are more â€Å"intelligent† than ever. Two areas of intelligence are noteworthy.First, today’s networks can offer differing levels of quality of service (QoS), which include specifications for maximum delay, minimum throughput, and so on. Second, today’s networks provide a variety of customizable services in the areas of network management and security. 1. 1 / DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE Speed (kbps) Transaction processing Messaging/text apps Voice Location services Still image t ransfers Internet/VPN access Database access Enhanced Web surfing Low-quality video Hifi audio Large file transfer Moderate video Interactive entertainment High-quality video Performance: Poor Adequate Good 9. 6 14. 4 28 64 144 384 2000 13 VPN: virtual private network Figure 1. 1 Services versus Throughput Rates 3.The Internet, the Web, and associated applications have emerged as dominant features of both the business and personal world, opening up many opportunities and challenges for managers. In addition to exploiting the Internet and the Web to reach customers, suppliers, and partners, enterprises have formed intranets and extranets1 to isolate their proprietary information free from unwanted access. 4. There has been a trend toward ever-increasing mobility for decades, liberating workers from the confines of the physical enterprise. Innovations include voice mail, remote data access, pagers, fax, e-mail, cordless phones, cell phones and cellular networks, and Internet portals.T he result is the ability of employees to take their business context with them as they move about. We are now seeing the growth of high-speed wireless access, which further enhances the ability to use enterprise information resources and services anywhere. 1 Briefly, an intranet uses Internet and Web technology in an isolated facility internal to an enterprise; an extranet extends a company’s intranet out onto the Internet to allow selected customers, suppliers, and mobile workers to access the company’s private data and applications. 14 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET Data Transmission and Network Capacity RequirementsMomentous changes in the way organizations do business and process information have been driven by changes in networking technology and at the same time have driven those changes. It is hard to separate chicken and egg in this field. Similarly, the use of the Internet by both businesses and individuals reflects this cycli c dependency: the availability of new image-based services on the Internet (i. e. , the Web) has resulted in an increase in the total number of users and the traffic volume generated by each user. This, in turn, has resulted in a need to increase the speed and efficiency of the Internet. On the other hand, it is only such increased speed that makes the use of Web-based applications palatable to the end user.In this section, we survey some of the end-user factors that fit into this equation. We begin with the need for high-speed LANs in the business environment, because this need has appeared first and has forced the pace of networking development. Then we look at business WAN requirements. Finally we offer a few words about the effect of changes in commercial electronics on network requirements. The Emergence of High-Speed LANs Personal computers and microcomputer workstations began to achieve widespread acceptance in business computing in the early 1980s and have now achieved virtu ally the status of the telephone: an essential tool for office workers.Until relatively recently, office LANs provided basic connectivity services—connecting personal computers and terminals to mainframes and midrange systems that ran corporate applications, and providing workgroup connectivity at the departmental or divisional level. In both cases, traffic patterns were relatively light, with an emphasis on file transfer and electronic mail. The LANs that were available for this type of workload, primarily Ethernet and token ring, are well suited to this environment. In the 1990s, two significant trends altered the role of the personal computer and therefore the requirements on the LAN: 1. The speed and computing power of personal computers continued to enjoy explosive growth. These more powerful platforms support graphics-intensive applications and ever more elaborate graphical user interfaces to the operating system. . MIS (management information systems) organizations hav e recognized the LAN as a viable and essential computing platform, resulting in the focus on network computing. This trend began with client/server computing, which has become a dominant architecture in the business environment and the more recent Webfocused intranet trend. Both of these approaches involve the frequent transfer of potentially large volumes of data in a transaction-oriented environment. The effect of these trends has been to increase the volume of data to be handled over LANs and, because applications are more interactive, to reduce the acceptable delay on data transfers.The earlier generation of 10-Mbps Ethernets and 16-Mbps token rings was simply not up to the job of supporting these requirements. The following are examples of requirements that call for higher-speed LANs: †¢ Centralized server farms: In many applications, there is a need for user, or client, systems to be able to draw huge amounts of data from multiple centralized servers, called server farms. An example is a color publishing operation, in 1. 1 / DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE 15 which servers typically contain tens of gigabytes of image data that must be downloaded to imaging workstations. As the performance of the servers themselves has increased, the bottleneck has shifted to the network. Power workgroups: These groups typically consist of a small number of cooperating users who need to draw massive data files across the network. Examples are a software development group that runs tests on a new software version, or a computer-aided design (CAD) company that regularly runs simulations of new designs. In such cases, large amounts of data are distributed to several workstations, processed, and updated at very high speed for multiple iterations. †¢ High-speed local backbone: As processing demand grows, LANs proliferate at a site, and high-speed interconnection is necessary. Corporate Wide Area Networking Needs As recently as the ear ly 1990s, there was an emphasis in many organizations on a centralized data processing model.In a typical environment, there might be significant computing facilities at a few regional offices, consisting of mainframes or well-equipped midrange systems. These centralized facilities could handle most corporate applications, including basic finance, accounting, and personnel programs, as well as many of the business-specific applications. Smaller, outlying offices (e. g. , a bank branch) could be equipped with terminals or basic personal computers linked to one of the regional centers in a transaction-oriented environment. This model began to change in the early 1990s, and the change accelerated through the mid-1990s. Many organizations have dispersed their employees into multiple smaller offices.There is a growing use of telecommuting. Most significant, the nature of the application structure has changed. First client/server computing and, more recently, intranet computing have funda mentally restructured the organizational data processing environment. There is now much more reliance on personal computers, workstations, and servers and much less use of centralized mainframe and midrange systems. Furthermore, the virtually universal deployment of graphical user interfaces to the desktop enables the end user to exploit graphic applications, multimedia, and other data-intensive applications. In addition, most organizations require access to the Internet.When a few clicks of the mouse can trigger huge volumes of data, traffic patterns have become more unpredictable while the average load has risen. All of these trends means that more data must be transported off premises and into the wide area. It has long been accepted that in the typical business environment, about 80% of the traffic remains local and about 20% traverses wide area links. But this rule no longer applies to most companies, with a greater percentage of the traffic going into the WAN environment [COHE 96]. This traffic flow shift places a greater burden on LAN backbones and, of course, on the WAN facilities used by a corporation.Thus, just as in the local area, changes in corporate data traffic patterns are driving the creation of high-speed WANs. Digital Electronics The rapid conversion of consumer electronics to digital technology is having an impact on both the Internet and corporate intranets. As these new gadgets come into view and proliferate, they dramatically increase the amount of image and video traffic carried by networks. Two noteworthy examples of this trend are digital versatile disks (DVDs) and digital still cameras. With the capacious DVD, the electronics industry has at last 16 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET found an acceptable replacement for the analog VHS videotape.The DVD has replaced the videotape used in videocassette recorders (VCRs) and replaced the CD-ROM in personal computers and servers. The DVD takes video into the di gital age. It delivers movies with picture quality that outshines laser disks, and it can be randomly accessed like audio CDs, which DVD machines can also play. Vast volumes of data can be crammed onto the disk, currently seven times as much as a CDROM. With DVD’s huge storage capacity and vivid quality, PC games have become more realistic and educational software incorporates more video. Following in the wake of these developments is a new crest of traffic over the Internet and corporate intranets, as this material is incorporated into Web sites. A related product development is the digital camcorder.This product has made it easier for individuals and companies to make digital video files to be placed on corporate and Internet Web sites, again adding to the traffic burden. 1. 2 A COMMUNICATIONS MODEL This section introduces a simple model of communications, illustrated by the block diagram in Figure 1. 2a. The fundamental purpose of a communications system is the exchange of data between two parties. Figure 1. 2b presents one particular example, which is communication between a workstation and a server over a public telephone network. Another example is the exchange of voice signals between two telephones over the same network. The key elements of the model are as follows: †¢ Source.This device generates the data to be transmitted; examples are telephones and personal computers. Source system Destination system Source Transmitter Transmission System (a) General block diagram Receiver Destination Workstation Modem Public telephone network (b) Example Modem Server Figure 1. 2 Simplified Communications Model 1. 2 / A COMMUNICATIONS MODEL 17 †¢ Transmitter: Usually, the data generated by a source system are not transmitted directly in the form in which they were generated. Rather, a transmitter transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system .For example, a modem takes a digital bit stream from an attached device such as a personal computer and transforms that bit stream into an analog signal that can be handled by the telephone network. †¢ Transmission system: This can be a single transmission line or a complex network connecting source and destination. †¢ Receiver: The receiver accepts the signal from the transmission system and converts it into a form that can be handled by the destination device. For example, a modem will accept an analog signal coming from a network or transmission line and convert it into a digital bit stream. †¢ Destination: Takes the incoming data from the receiver.This simple narrative conceals a wealth of technical complexity. To get some idea of the scope of this complexity, Table 1. 1 lists some of the key tasks that must be performed in a data communications system. The list is somewhat arbitrary: Elements could be added; items on the list could be merged; and some items repr esent several tasks that are performed at different â€Å"levels† of the system. However, the list as it stands is suggestive of the scope of this book. The first item, transmission system utilization, refers to the need to make efficient use of transmission facilities that are typically shared among a number of communicating devices.Various techniques (referred to as multiplexing) are used to allocate the total capacity of a transmission medium among a number of users. Congestion control techniques may be required to assure that the system is not overwhelmed by excessive demand for transmission services. To communicate, a device must interface with the transmission system. All the forms of communication discussed in this book depend on the use of electromagnetic signals propagated over a transmission medium. Thus, once an interface is established, signal generation is required for communication. The properties of the signal, such as form and intensity, must be such that the signal is (1) capable of being propagated through the transmission system, and (2) interpretable as data at the receiver.Not only must the signals be generated to conform to the requirements of the transmission system and receiver, but also there must be some form of synchronization Table 1. 1 Communications Tasks Transmission system utilization Interfacing Signal generation Synchronization Exchange management Error detection and correction Flow control Addressing Routing Recovery Message formatting Security Network management 18 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET between transmitter and receiver. The receiver must be able to determine when a signal begins to arrive and when it ends. It must also know the duration of each signal element.Beyond the basic matter of deciding on the nature and timing of signals, there is a variety of requirements for communication between two parties that might be collected under the term exchange management. If data are to be exchanged in both directions over a period of time, the two parties must cooperate. For example, for two parties to engage in a telephone conversation, one party must dial the number of the other, causing signals to be generated that result in the ringing of the called phone. The called party completes a connection by lifting the receiver. For data processing devices, more will be needed than simply establishing a connection; certain conventions must be decided on.These conventions may include whether both devices may transmit simultaneously or must take turns, the amount of data to be sent at one time, the format of the data, and what to do if certain contingencies such as an error arise. The next two items might have been included under exchange managem