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Evolution of computer networks

Evolution of computer networks. Chapter 1: Outline. 1.1 Data Communications 1.2 Networks 1.3 Network Types 1.4 Internet History 1.5 Standards and Administration. Chapter 1: Objective.

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Evolution of computer networks

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  1. Evolution of computer networks

  2. Chapter 1: Outline 1.1 Data Communications 1.2 Networks 1.3 Network Types 1.4 Internet History 1.5 Standards and Administration

  3. Chapter 1: Objective • The first section introduces data communications and defines their components and the types of data exchanged. It also shows how different types of data are represented and how data is flowed through the network. • The second section introduces networks and defines their criteria and structures. It introduces four different network topologies that are encountered throughout. • The third section discusses different types of networks: LANs, WANs, and internetworks (internets). It also introduces the Internet, the largest internet in the world. The concept of switching is also introduced in this section to show how small networks can be combined to create larger ones.

  4. Chapter 1: Objective (continued) • The fourth section covers a brief history of the Internet. The section is divided into three eras: early history, the birth of the Internet, and the issues related to the Internet today. • The fifth section covers standards and standards organizations. The section covers Internet standards and Internet administration.

  5. 1-1 DATA COMMUNICATIONS When we communicate, we are sharing information. This sharing can be local or remote. The term telecommunication, which includes telephony, telegraph, and television, means communication at a distance. Data communications are the exchange of data between two devices via some form of transmission media.

  6. 1.1.1 Components A data communications system has five components (see Figure 1.1).

  7. Figure 1.1: Five components of data communication

  8. 1.1.2 Data Representation Information today comes in different forms such as text, numbers, images, audio, and video.

  9. 1.1.3 Data Flow Communication between two devices can be simplex, half-duplex, or full-duplex as shown in Figure 1.2.

  10. Figure 1.2: Data flow

  11. 1-2 NETWORKS A network is the interconnection of a set of devices capable of communication. In this definition, a device can be a host such as a large computer, desktop, laptop, workstation, cellular phone, or security system. A device in this definition can also be a connecting device such as a router a switch, a modem that changes the form of data, and so on.

  12. 1.2.1 Network Criteria A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security.

  13. Performance Depends on Network Elements Measured in terms of Delay and Throughput Reliability Failure rate of network components Measured in terms of availability/robustness Security Data protection against corruption/loss of data due to: Errors Malicious users Network Criteria

  14. 1.2.2 Physical Structures Before discussing networks, we need to define some network attributes. • Type of Connection • Point to Point - single transmitter and receiver • Multipoint - multiple recipients of single transmission • Physical Topology • Connection of devices • Type of transmission - unicast, mulitcast, broadcast

  15. Figure 1.3: Types of connection

  16. Figure 1.4: A fully-connected mesh topology

  17. Figure 1.5: A star topology

  18. Figure 1.6: A bus topology

  19. Figure 1.7: A ring topology

  20. 1-3 NETWORKS TYPES After defining networks in the previous section and discussing their physical structures, we need to discuss different types of networks we encounter in the world today. The criteria of distinguishing one type of network from another is difficult and sometimes confusing. We use a few criteria such as size, geographical coverage, and ownership to make this distinction.

  21. Local Area Networks (LANs) Short distances Designed to provide local interconnectivity Wide Area Networks (WANs) Long distances Provide connectivity over large areas Metropolitan Area Networks (MANs) Provide connectivity over areas such as a city, a campus Categories of Networks

  22. 1.3.1 Local Area Network A local area network (LAN) is usually privately owned and connects some hosts in a single office, building, or campus. Depending on the needs of an organization, a LAN can be as simple as two PCs and a printer in someone’s home office, or it can extend throughout a company and include audio and video devices. Each host in a LAN has an identifier, an address, that uniquely defines the host in the LAN. A packet sent by a host to another host carries both the source host’s and the destination host’s addresses.

  23. Figure 1.8: An Isolated LAN in the past and today

  24. 1.3.2 Wide Area Network A wide area network (WAN) is also an connection of devices capable of communication. However, there are some differences between a LAN and a WAN. A LAN is normally limited in size; a WAN has a wider geographical span, spanning a town, a state, a country, or even the world. A LAN interconnects hosts; a WAN interconnects connecting devices such as switches, routers, or modems. A LAN is normally privately owned by the organization that uses it; a WAN is normally created and run by communication companies and leased by an organization that uses it.

  25. Figure 1.9: A Point-to-Point WAN

  26. Figure 1.10: A Switched WAN

  27. Figure 1.11: An internetwork made of two LANs and one WAN

  28. Figure 1.12: A heterogeneous network made of WANs and LANs

  29. Wide Area Network

  30. 1.3.3 Switching An internet is a switched network in which a switch connects at least two links together. A switch needs to forward data from a network to another network when required. The two most common types of switched networks are circuit-switched and packet-switched networks. We discuss both next.

  31. Figure 1.13:A circuit-switched network

  32. Figure 1.14: A packet-switched network

  33. 1.3.4 The Internet As we discussed before, an internet (note the lowercase i) is two or more networks that can communicate with each other. The most notable internet is called the Internet (uppercase I ), and is composed of thousands of interconnected networks. Figure 1.15 shows a conceptual (not geographical) view of the Internet.

  34. Figure 1.15: The Internet today

  35. 1.3.5 Accessing the Internet The Internet today is an internetwork that allows any user to become part of it. The user, however, needs to be physically connected to an ISP. The physical connection is normally done through a point-to-point WAN. In this section, we briefly describe how this can happen, but we postpone the technical details of the connection until Chapters 14 and 16.

  36. 1-4 INTERNET HISTORY Now that we have given an overview of the Internet and its protocol, let us give a brief history of the Internet. This brief history makes it clear how the Internet has evolved from a private network to a global one in less than forty years.

  37. 1.4.1 Early History There were some communication networks, such as telegraph and telephone networks, before 1960. These networks were suitable for constant-rate communication at that time, which means that after a connection was made between two users, the encoded message (telegraphy) or voice (telephony) could be exchanged. A computer network, on the other hand, should be able to handle bursty data, which means data received at variable rates at different times. The world needed to wait for the packet-switched network to be invented.

  38. 1.4.2 Birth of the Internet In 1972, Vint Cerf and Bob Kahn, both of whom were part of the core ARPANET group, collaborated on what they called the Internetting Project. They wanted to link dissimilar networks so that a host on one network could communicate with a host on another. There were many problems to overcome: diverse packet sizes, diverse interfaces, and diverse transmission rates, as well as differing reliability requirements. Cerf and Kahn devised the idea of a device called a gateway to serve as the intermediary hardware to transfer data from one network to another.

  39. 1.4.3 Internet Today Today, we witness a rapid growth both in the infrastructure and new applications. The Internet today is a set of pier networks that provide services to the whole world. What has made the Internet so popular is the invention of new applications. 1. Organization of the Internet 2. Internet Service Providers (ISPs)

  40. 1-5 STANDARDS AND ADMINISTRATION In the discussion of the Internet and its protocol, we often see a reference to a standard or an administration entity. In this section, we introduce these standards and administration entities for those readers that are not familiar with them; the section can be skipped if the reader is familiar with them.

  41. 1.5.1 Internet Standards An Internet standard is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. It is a formalized regulation that must be followed. There is a strict procedure by which a specification attains Internet standard status. A specification begins as an Internet draft. An Internet draft is a working document (a work in progress) with no official status and a six-month lifetime.

  42. Figure 1.16: Maturity levels of an RFC

  43. 1.5.2 Internet Administration The Internet, with its roots primarily in the research domain, has evolved and gained a broader user base with significant commercial activity. Various groups that coordinate Internet issues have guided this growth and development. Figure 1.17 shows the general organization of Internet administration.

  44. Figure 1.17: Internet administration

  45. 1-4 PROTOCOLS A protocol is synonymous with rule. It consists of a set of rules that govern data communications. It determines what is communicated, how it is communicated and when it is communicated. The key elements of a protocol are syntax, semantics and timing Topics discussed in this section: • Syntax • Semantics • Timing

  46. Syntax Structure or format of the data Indicates how to read the bits - field delineation Semantics Interprets the meaning of the bits Knows which fields define what action Timing When data should be sent and what Speed at which data should be sent or speed at which it is being received. Elements of a Protocol

  47. Review Questions 1. A computer network interconnects a number of _____________ computers. 2. Computer network emerges due to the development between two fields, namely _____________ and _____________. 3. Three main categories of networks are _____________, _____________ and _____________. 4. _____________ are privately owned while _____________ are usually owned by government 5. LAN operates at a _____________ speed with _____________error rate than WANs. 6. Internet is _____________ of networks. 7. Initially, computer network was developed for ________________.

  48. Q-1. Which Technologies of this age had led to the emergence of computer network? Q-2. What are the two broad classifications under which Networks can be divided? Q-3. Mention different categories of computer networks (on the basis of scale) and distinguish one from the other. Q-4. What are the two types of Transmission technologies, basis on which computer networks can be categorized? Q-5. What is Internet? Q-6. How do you account for higher reliability and scalability of computer network? Q-7. Mention important benefits of computer network. Q-8. What are the main categories based on which applications of computer network can be categorized? Q-9. How is computer networks used in marketing and sales, financial services, teleconferencing? TRY YOURSELF

  49. References: • Textbooks: • Data Communications and Networking, Behrouz A. Forouzan, TMH • 2. Data and Computer Communications, William Stallings, • PHI • 3. Computer Networks, Andrew S. Tanenbaum, PHI Reference books: 1. Wireless Communications; Principles and Practice, Theodore E. Rappaport, 2nd Edition, Pearson Education 2. Satellite Communications, Timothy Pratt, Charles Bostian and Jeremy Allnutt, 2nd Edition, Wiley 3. Internetworking with TCP/IP; Principles, Protocols and Architecture, Douglas E. Commer, 3rd Edition, Prentice Hall of India 4. Data Compression; The Complete Reference, David Solomon, 3rd Edition, Springer 5. Network Security; Private Communication in a Public World, CharlieKaufman, Radia Perlmon and Mike Speciner, 2nd Edition, Prentice Hall of India

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