Refelction paper about Identity and possibility Article

Refelction paper about Identity and plausibility - Article Example Or maybe, it is the totality of regular living encounters and is a procedure that creates among disillusionments, triumphs and ordinary everyday environments that develops the character of an individual. Self-comprehension is the essential manifestation of a person’s personality. We become who we figure ourselves to become and this is every day. It is not necessarily the case that a manner is precarious, unexpectedly, it is a mix of steadiness of character. The advancement of one’s character is the mixing of every single human action and connections among exact points of view. It isn't just inside the dividers of the school that an adolescent’s personality is created. A greater amount of it is through the connections and exercises that they supply themselves into. These are the things that they accomplish the most guilty pleasure from and in this manner would destined to shape them towards a personality that would frame them into what's to come. The famous inquiry of â€Å"Who am I?† is one that is frequently replied with regards to correspondence from these center character molding matters. Similarly as with the subject exemplified by the creator through Mac, the 14-year old kid who consistently gets into a battle. A derivation of this idea would compare that in the limits of the school he would be seen as a troublesome kid. However, a profound examination of the child’s mental reasoning uncovers that he is somebody who can be relied on by his loved ones in the example that his assistance is required. It can't then be reasoned that he is a loner just based on his school records and the numerous fights he gets himself in. Personality emergency is another significant trouble that emerges inside this age gathering. A â€Å"developmental moratorium† as introduced by Erikson in his model is essential for youths to enlarge their capacity of development as they are permitted to explore among differed encounters as they continued looking for personality. It is an open door for them to utilize

Professional Sports and Michael Pore Essay Example for Free

Elite athletics and Michael Pore Essay Competitors are nearly as awful of good examples as lawbreakers. Competitors get called good examples a ton yet they don't fit the meaning of a good example. Competitors set awful models for teenagers. They settle on poor decisions and are handily pardoned because of their athletic capacities. Competitors are awful good examples for youngsters and children on the grounds that a ton of competitors have unfortunate propensities, set unreasonable desires, and set awful models. Regardless of their capacities, competitors are bad good examples for anybody of all ages. Numerous competitors have negative behavior patterns like medication use, battling, and betting. Laura K. Egendorf says numerous ridiculous desires are set; not every person can become celebrated or an expert competitor. Such a large number of teenagers and children admire significant competitors so they ought not be setting the terrible models that they are setting (Laura K. Egendorf, 64). Not exclusively are they setting terrible models yet they have negative behavior patterns too. Additionally, as youngsters develop more established they read about their competitor legend and their negative behavior patterns. Michael A. Pore states that any law breaking or wrong thing an expert competitor does, there is a story posted in paper, on the web, or even said on TV. Michael Jordan had a betting issue, Sammy Sosa had a steroid issue, and Riddick Bowe had a battling issue (Michael A. Pore, 41). A few adolescents acknowledge competitors are bad good examples. Proficient competitors are handily excused for their errors. Be that as it may, proficient competitors set terrible models for teenagers and youthful competitors. Michael A. Pore expresses that competitors are excessively effectively excused for their terrible conduct. You don’t need to utilize medications to be acceptable at something. They feel cash comes effectively, however cash isn't all that matters and doesn't come without any problem. Competitors send negative messages to kids; on the off chance that you purchase a specific item the competitor advances, you won't perform better (Michael A. Pore, 40). Not every person will play out the manner in which proficient competitors do and get celebrated. In Addition, competitors set unreasonable desires for the adolescents and children admiring them. Not every person can and will turn into an expert competitor. Not many individuals will make a great many dollars a year only for playing a game. Michael A. Pore says teenagers feel in the event that they wear a brand advanced by a competitor they will fit in with the remainder of the players playing the game. For the children admiring the expert competitors, they believe they need to look as solid as them or be as strong as them to plat the game well (Michael A. Pore, 43). A couple of competitors get their solid look from steroids, not real quality. Be that as it may, steroid use isn't that terrible every so often. In the article, Athletes Are Role Models it states; If you lack the capacity to deal with training, steroids improve your exhibition. Steroids cause you to feel better when you do well in your game. Nobody will know whether you do it on occasion (http://www. ickscorner. com). Steroids can help anybody any age. Regardless, nobody of all ages should utilize steroids. Steroids are an unlawful substance and in the event that you get discovered utilizing them you can get a gigantic fine or even prison time. On the off chance that you use steroids, you are simply swindling yourself and the game. In addition to the fact that steroid uses get looked down on it slaughters synapses (http://gathering. weight training. com). On the off chance that you don't have the opportunity to practice and feel like that is motivation to utilize steroids and perform better, than you ought not have the opportunity to be in the group. Appropriately, competitors can set reasonable desires and help adolescents and children go for their fantasies. Laura K. Egendorf clarifies how most small children and youngsters need to be well known when they are more seasoned; proficient competitors assist them with going after that fantasy. As teenagers develop more established, they keep on viewing their preferred proficient competitor. Watching them do well in a game will make teenagers need to perform like them (Laura K. Egendorf, 64). Proficient competitors rake in tons of cash only for playing a game, yet cash isn't all that matters. Then again, numerous children and teenagers get propelled however is it sensible? Not many individuals on the planet become acclaimed. The odds of turning into an expert competitor are tiny; there are around 301,000,000 individuals in the United States and just around 17,000 expert competitors. â€Å"http://gathering. weight training. com† resembling an expert competitor isn't in every case great; drugs are not something beneficial for a youngster to get into. Therefore, competitors ought not be good examples for anybody of all ages; they have negative behavior patterns, set unreasonable desires, and set terrible models. A great deal of competitors have unfortunate propensities like steroid use and betting. Proficient competitors set unreasonable models, not every person can and will be well known. Numerous terrible models are set inside competitors. Individuals get spurred for unreasonable dreams. Competitors can show youngsters how to attempt to accomplish in sports yet they can’t help with schoolwork or genuine family issues, they ought not be viewed as good examples.

7 Ways to Deep Clean Your Resume

7 Ways to Deep Clean Your Resume In preparation for going away for the Thanksgiving holiday, I decided to “deep clean” my kitchen. As I was wiping down the back panel of my stove (the one with all the buttons), it struck me that the Whirlpool logo was light blue. I had never thought twice about the color of that logo in the four years I had lived in this apartment. But now I got curious, and discovered a light blue protective sticker covering up the silver Whirlpool logo that was meant to ornament the stove. I pulled it off, and the appliance now seems just a little bit newer: It shines the way it was intended. Moving on to the sink, I discovered a similar sticker on the metal container that holds my scrubbies. I pulled that one off too. It’s like I have a whole new look to my kitchen! This experience got me thinking: Where else in our lives do we stare at something day after day, accepting it as part of our environment, without thinking to look more carefully? Where do we blindly accept messes and errors that could easily be peeled back to reveal something shiny underneath? Deep Clean Your Resume One place a lot of people have become blind to errors is on their resumesâ€"one area where it is most important to be squeaky clean. Below are seven common spots to look for possible cleaning opportunities: Address, phone and email. Although it’s unlikely you have misspellings in any of these key areas, perhaps you changed a phone number or email address and forgot to change it on your resume? Make sure your address, phone and email are not just correct but also up to date! If you are in a technology field, use a gmail address or paid account and stay away from hotmail and yahoo. Section headings. Have you checked the spelling of the word Achievements (I have seen senior executives’ resumes where the heading is spelled Acheivements)? How about Experience and Activities? Are there any extra letters floating around? Did you correctly spell Extracurricular (I have seen Extracaricular). Not only could errors like these turn off a hiring manager who notices them, but they could prevent an ATS system from recognizing an entire section of your resume. Job titles. One of the most commonly misspelled words on resumes is “Manager” (often spelled “Manger”). Check your job titles to make sure they are spelled correctly! Verbs. “Led” is the past tense of “Lead” (many people mistakenly write “Lead”). Also, are you repeating your verbs over and over in various bullets? See what you can do to vary your verbs! Your resume will truly start to shine. And finally, make sure your past jobs use past tense verbs! Often when someone converts a present job to a past job, some of those verbs remain in the present tense. This applies to ALL verbs in the section, not just the ones that start each bullet. For more tips on varying your verbs, view my webinar, Top 10 Ways to Make Resume Writing FUN! Format. Do all your bullets and dates line up with each other? Do you use the same font and font size throughout your resume (unless you have an artistic, consistent reason for using two different fonts)? Is your spacing even? Are your headers all formatted the same way? If not, you have some cleaning up to do! Dates. Line up all your dates format-wise and use consistent formatting (don’t write 1/06 to 2/05 in one spot and 3/2008-4/2011 in another; don’t write December 2004 in one spot and Dec. 2006 in another). Check that all dates are accurate, with proper months and years, listed in reverse chronological order. Also see tip #4 on using past tense verbs consistently in your past jobs. Document Properties and Tracked Changes. If someone else assisted you with your resume, there might be tracked changes and document properties still lurking. To clean up tracked changes, accept all changes and delete all comments. Want more detailed instructions? Check out my article, How to Avoid Embarrassing Editing Marks on Your Documents! To delete document properties such as Author, go to the File tab, click on Check for Issues and then Inspect document. Follow the prompts and your document will be cleaned of whatever information you choose. If you’re applying for jobs or plan to do so in the future, you will benefit from “deep cleaning” your resume. Do you have additional ideas of steps you can take? Surprise errors found? Please share below, and scrub your resume so that, like the Whirlpool logo on my stove, your accomplishments can shine the way they were intended!

The Ethics of Abortion - 2307 Words

Background and Context Abortion is defined as a procedure that is done to remove an embryo or fetus from the uterus of its mother in order to prevent its birth (Roth, 2005). Abortion is categorized as a bioethical issue because it relates to the morals of biomedical advances, policies and research. Abortion is a difficult subject that can involve personal morals and beliefs, legality and religious values. The issue is often viewed from either the side of pro-life, which places emphasis on the fetus and its right to life or pro-choice, which emphasizes the rights of the mother to decide the appropriate action (Roth, 2005). This brings the ethical question of should the government have the right to outlaw abortion into debate. The two†¦show more content†¦In the United Sates, viability is around 24 weeks or pregnancy (Roth, 2005). Viability is defined as the ability of the fetus to live outside of the uterus after birth (Jones, 2007). The autonomy of the mother is addressed with the argument that the mother has the right to decide if she wants to carry the fetus full term or abort it (Jones, 2007). This argument presents that the mother has the right to her life and her body, therefore she gets to choose what is done with the fetus. The mother should not be forced to have the child against her will because this would be immoral and infringe on her rights (Jones, 2007). The right to life of the fetus is addressed with the argument that the fetus has the same equal right to life that all people do (Jones, 2007). An extension of this argument is that society has the moral duty to protect the fetus because it is incapable of protecting itself. Another argument indicates that the fetus is only a potential life since it depends on the mother for existence. This means some consider the mother to be a fully formed life and have a higher value than the fetus (Jones, 2007). Others argue that the fetus is a life that should be valued from the moment of conception because it is part of the â€Å"human community† and has intrinsic value (Nobis, 2011). Judith Jarvis Thomson, a philosopher, makes the argument that a fetus may be considered a person but abortion may still be morally justified (1971). Thomson uses the thoughtShow MoreRelatedEthics And Abortion : Abortion Essay1724 Words   |  7 PagesEthics And Abortion According to the authors of a medical dictionary called; the free dictionary, online version, â€Å"abortion is defined as the termination of pregnancy before the fetus is viable.† Viability for a fetus is usually greater than 500 grams, or prior to 20 weeks gestation as noted by those same authors. An abortion may be spontaneous, commonly referred to as a miscarriage, or induced which describes the deliberate interruption of a pregnancy. Those authors assert that it is the viabilityRead MoreThe Ethics Of Abortion And Abortion1124 Words   |  5 PagesThe Ethics of Abortion Abortion, which according to the Merriam Webster dictionary (n.d.) refers to any action that is taken to prematurely end the life of a growing fetus in its mother’s womb before it is born, is a very controversial topic in our society today. Every day, several women die as a result of lack of access to proper abortion facilities (Kaczor, 2013). It has been estimated that 2% of women within childbearing age i.e. ages 15 to 44 will have an abortion (Medoff, 2013) and the yearlyRead MoreThe Ethics And Ethics Of Abortion1496 Words   |  6 PagesTHE ETHICS AGAISNT ABORTION Abortion has been one of the most debated social and political topics since it was made legal in South Africa. Through the application of different philosophical arguments this paper will showcase in detail if abortion is either immoral or permissible using ethical underpinnings (cite 2). In this essay abortion will be defined as the deliberate removal of a fetus from the womb of a human female through the request of the mother resulting in the death of the fetus. AbortionsRead MoreEthics of Abortion1933 Words   |  8 PagesEthics of Abortion Destiny Vazquez SOC 120 Instructor Slack Monday, April 16, 2012 Abortion, one of the most ethical issues debated today. It has been a widely controversial debate for many years dated back to even before it was made legal in the United States. Like most ethical issues, there are two sides as to what is the right thing to do. Some people think that abortion is completely and utterly wrong. Some people think that abortion is right when and only when the mother’s life is atRead MoreEthics: Nursing and Abortion1645 Words   |  7 PagesDupin, Jenifer June 8, 2013 Ethics/ Research Proposal The Ethics for Nurses in Abortion Procedures Working in the field of abortion isn’t an easy task furthermore participating in the abortion procedures. But the field of nursing you have to follow a code of ethics, a set of rules and regulation. Nurses have their personal opinions about abortion, but because they are health professionals and their opinions are sought as such, they are obligated to understand why they hold certain views. NursesRead MoreEssay on The Ethics of Abortion1070 Words   |  5 PagesThe Ethics of Abortion The Ethics Of Abortion is a very controversial subject that has been continually argued over for the past few years and probably many more years to come. The main controversy is should abortion remain legalized? Before we get into the many sides of abortion we must first define abortion. Abortion is the destruction of the fetus or unborn child while the child is still in the mother’s womb. This can be done by almost anyone from the mother herself to back alley abortionsRead More Abortion Ethics Essay882 Words   |  4 Pages The argument of abortion has been raging since the Supreme Court case, Roe vs. Wade, in 1973. This court case has divided the country into two factions: pro-choice and pro-life. Pro-life advocates argue that abortions are murder and extreme levels of child abuse. While pro-choice advocates believe abortions are a justifiable means to end pregnancies. The pro-choice argument is that the fetus is not yet a human being and its rights should not override that of the mother’s. An importance on whatRead MoreThe Ethics And Morals Of Abortion Essay1643 Words   |  7 PagesThe Ethics and Morals of Abortion Abortion, as it is, is a method to terminate a pregnancy by removing a fetus or an embryo out of the woman’s uterus. It is one of the most controversial problematic issues that is discussed throughout the decades. The topic of abortion was considered as a social issue that soon became a political and ethical subject. Abortion have become a heated public distribute on whether its method are morally permissible or not? Individuals have voiced the benefits and disadvantagesRead MoreThe Article Ethics Of Abortion1869 Words   |  8 PagesIn the article Ethics of Abortion, much of the pro life argument seems to be rooted in religion, alongside the concern for safety. However, it is unethical to make a law based on religion and the safety concerns have pros and cons to both sides. Because of the extremely diverse circumstances, it is hard to make an ultimatum such as the banning of abortion. Abortion should, therefore, be legal and accessible in the U.S. because of our human rights, multitude of safety concerns and theRead MoreThe Article Ethics Of Abortion1869 Words   |  8 PagesIn the article Ethics of Abortion, much of the pro life argument seems to be rooted in religion, alongside the concern for safety. However, it is unethical to make a law based on religion and the safety concerns have pros and cons to both sides. Because of the extremely diverse circumstances, it is hard to make an ultimatum such as the banning of abortion. Abortion should, therefore, be legal and accessible in the U.S. because of our human rights, multitude of safety concerns and the

Essay Feminism and feminist social theory - 1100 Words

Feminism and feminist social theory unlike other theoretical perspectives is woman-centered and inter-disciplinary, hence promotes methods of achieving social justice. The feminism and feminist social theory takes into consideration three questions, what of the women? Why is the present social world as it is today? Additionally, how can the social world be changed to make it more just for the women and all people alike? In recent developments, feminist theorists have begun questioning the differences between women. The areas under question include race, ethnicity, class, age intersect, and gender. In summation, the feminist theory involves the concern with giving women world over voice, and highlighting how they have contributed to the†¦show more content†¦The term gender refers to the characteristics of a person despite the person’s biological sex. Gender role, which is the focus of sociologists, is the anticipated attitude and behavior that a certain society connect s with each sex. With this definition, gender is placed evenly in the sociocultural context. Events that previously occurred had a vital impact on gender roles. Due to this, the study of gender emerged as one of the significant disciplines in the field of sociology in the twentieth century. The gender issues were studied using various research and theory. The research on gender issues provided a testament that all social interactions that occur, and the institutions where they occur, are gendered in one way or the other. Sociologists explain gender roles with respect to various theoretical perspectives. The perspectives are the ways of perceiving social reality that guide the process of research and provide a method for understanding the data. The sociological perspectives on gender roles include functionalism, conflict theory, symbolic interaction, and feminist sociological theory (pearsonhighered.com). The functionalism theory is also known as structural functionalism and lays cla im on the fact that the society is composed of interdependent portions each of which adds to the functioning of the whole society. Functionalists breakShow MoreRelatedEssay on Feminism and Modern Feminist Theory1068 Words   |  5 Pages Feminism is a body of social theory and political movement primarily based on and motivated by the experiences of women. While generally providing a critique of social relations, many proponents of feminism also focus on analyzing gender inequality and the promotion of womens rights, interests, and issues. Feminist theory aims to understand the nature of gender inequality and focuses on gender politics, power relations and sexuality. Feminist political activism campaigns on issues such asRead MoreFeminism1121 Words   |  5 PagesFEMINISM Introduction to Sociology Feminism Belief in the social, political, and economic equality of the sexes. The movement organized around this belief. Feminism Feminist Theory is an outgrowth of the general movement to empower women worldwide. Feminism can be defined as a recognition and critique of male supremacy combined with efforts to change it. Feminism The goals of feminism are: To demonstrate the importance of women To reveal that historically women have been subordinate to menRead More The Feminism Movement Essay1308 Words   |  6 PagesFor many years the word, â€Å"Feminism† has developed many different meanings and various people interpret this word in different ways. I interviewed five people who are close to me and I wrote down their responses to the questions, â€Å"What do you think Feminism is?† and â€Å"Do you consider yourself to be a feminist?† There were many different responses to these questions. I first interviewed my friend, Jordan. He mentioned that he believes feminism is about, â€Å"Power crazy, mannish women who think they areRead MoreFeminism : The Quality Of Life For Women1242 Words   |  5 PagesTimothy Truax October 1, 2014 Traditions of Feminism There is no one definite conclusion that makes up feminist ideals; it is rather a compilation of theories set to achieve a common goal, the enhancement of the quality of life for women. Since the first wave of feminist thought began back in 1835, there have been extensive changes in the opinions of individual feminists. There have been three main waves of feminist theories each yielding its own unique opinion on how to achieve their common goalRead MoreCritically Examine How Black Feminism Emerged And Assess1229 Words   |  5 PagesBlack feminism emerged and assess its impact on contemporary feminist theory. Answer with reference to intersectionality and ‘difference . feminism means the equality between men and women in social, political and social standing. There are many different types of feminism that women have adopted that they best feel aligns with their perspectives of the world. This essay will mainly be focusing black feminism that was developed in the 1960s. The essay will examine why the black feminism movementRead MoreSocial Reaction Theory And Feminist Theory Of Crimes1476 Words   |  6 Pages Social Reaction Theory and Feminist Theory of Crimes are the subject theories I am going to review, examine, and explain. I will be discussing the evolution of social reaction and labeling theory, which is mainly concerned with how individuals’ personal identities are highly influenced by the way that society has a tendency to classify them as offenders. I will also be reviewing the various forms of feminist theories, which began as reactions to the lack of reasonable theorizing about why femalesRead MoreFeminist Theory1345 Words   |  6 PagesFeminist Theory Feminist theory is the extension of feminism into theoretical, or philosophical discourse, it aims to understand the nature of gender inequality. It examines womens social roles and lived experience, and feminist politics in a variety of fields, such as anthropology and sociology, communication, psychoanalysis, economics, literary criticism, education, and philosophy. While generally providing a critique of social relations, much of feminist theory also focuses on analyzing genderRead MoreThe Core Themes Of Postcolonial Theory963 Words   |  4 Pagescore themes of postcolonial feminist theory. We shall define and critically assess themes such as intersectionality and the use of standpoint theory as an epistemological position, as well as analysing the importance of sexuality to post colonial theory. In order to support our findings we shall reference key authors such as Gavatri Spivak, Patricia Hill Collins and Audre Lorde, as their work will aid in providing examples of key postc olonial themes.   Postcolonial feminism was born in part as a reactionRead MoreFeminism And The Postmodern Feminist Theory1596 Words   |  7 PagesThe evolution of feminist theory from a modern to a postmodern viewpoint stands to correct the injustices of historically liberal feminism. For some time, grand narratives have governed the ideas of self and gender from a single experience of â€Å"man†. Traditionally, modern feminism aimed to eradicate the hegemonic theory of inferiority by women to the male gender. Postmodern feminism aspires to eliminate categories of gender altogether, for the social construct of gender is considered to disregardRead MoreFeminism : A Feminist Perspective1168 Words   |  5 Pagesactivism has influenced my intellectual journal through feminist theory. Feminism is a contentious topic with matters that pertain to contemporary feminism, including the following: reproductive rights; equal access to education and employment; marriage equality; violence against women ; and the sex trade. While these are only a few of the issues faced by feminists, it is evident that feminism has great value in today’s society. My journey with feminism began in high school when a professor shared negative

Data and Computer Communications Free Essays

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. We will write a custom essay sample on Data and Computer Communications or any similar topic only for you Order Now 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 Buyer: 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 P earson 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 ATS WEB 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 Confi guration 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 Site 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 Re ading 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. St atistical 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 Conne ctions 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 Traffic 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 Signal 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 Co ntrol 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 Management 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 Data 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 Refer ences 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 O nes-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 Form This 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 piece, 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 includes 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 information for an Internet mailing list for instruct ors 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/repor t 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 the 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 impleme ntations. †¢ 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. Jingxian 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 produced 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 flattering 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 networks. 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, chapter-by-chapter summary of each part appears at the beginning of that part. 0. 2 / ROADMAP 3 0. 2 ROADMAP Course Emphasis The 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 m ore 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 supported 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 GUIDE Part One Overview Part Two Data Communications Part Three Wide Area Networks Part Four Local Area Networks Part Five Internet and Transport Protocols Part Six Internet 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); Chapter 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 soon 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 information 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 ove r 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 obtain ing 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 equipme nt. 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. This 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 th e 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 communications. 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, and 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 bodies 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 Communications, 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 result 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 facilities 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. Trends Three 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 expands. 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-distance 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 transfers 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. The 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 Requirements Momentous 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 cyclic 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 virtually 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 have recognized the LAN as a viable and essential computing platform, resul ting 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 early 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 fundamentally 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 [COHE96]. 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 digital 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 represent 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 How to cite Data and Computer Communications, Essay examples

No Prayer For The Dying free essay sample

With the coming of Iron Maidens eighth album, a few changes have occurred with the band. The most noticeable is their new label. From 1980-1988 they had been with EMI/Capitol Records. However, their most recent album is their first with Epic Records, which hints at a possible new contract. Its possible that even though the band has been around for eleven years, we may continue to see more from them in the future. Along with the label change, they also replaced one of their lead and rhythm guitarists, Adrian Smith (co-writer of previous songs like Moonchild, The Evil That Men Do, etc.) with Janick Gers. So far, Gers has not participated in any songwriting. The influence of Smiths songwriting has not completely disappeared from their new album since the song Hooks in You was written some time before he left the band. Bass guitarist, Steve Harris, wrote two new songs which appear on No Prayer One of them, Mother Russia, is a song about the current revolution in the Soviet Union. We will write a custom essay sample on No Prayer For The Dying or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page Harris also co-wrote the first track on the album, Tailgunner, with front-man Bruce Dickinson. That song, like many other hard-hitters from Iron Maiden, is about the Allies bombing of Germany during World War II. With European history as a major source of the bands songwriting material, Iron Maiden has created an interesting, mythical and definitely original sound for themselves. Iron Maiden must be doing something right because although they receive no radio air play in England (their homeland), they still hit number one with almost every release. A good example was their first release off No Prayer called Bring Your Daughter to the Slaughter, which hit number one almost immediately after release. The band gets no radio air play in the U.S. either, yet a huge number of their fans live here. MTV is willing to air many Iron Maiden videos but this is restricted to only one show (Headbangers Ball) which airs once a week and even then the bands videos are rare. Nevertheless, Iron Maiden is still going strong and selling multi-platinum albums consistently. n