Lecture of computer communication and networks chapter 1

CSC340-Computer Networks Muhammad Usman Nasir Email: usmannasir@cuisahiwal.edu.pk Marks Distribution Activity Marks Mid Term 25 Quizzes (Minimum 4) 15 Assignments (Minimum 4) & Project 10 Final 50

1.2 Chapter 1 • Data communications and networking are changing the way we do business and we live. • Business decisions have to be made ever more quickly, and the decision makers require immediate access to accurate information like in stock market. • No need to wait a week for the report to arrive from abroad mail, rather it could appear almost instantaneously through computer networks, i.e., email. • The development of the personal computer brought about tremendous changes for business, industry, science, and education. • A similar revolution is occurring in data communications and networking. • Technological advances are making it possible for communication links to carry more data and faster signals • Research in data communications and networking has one major goal: to be able to exchange data such as text, audio, and video from all points in the world. This chapter addresses following issues: •Data communications: information sharing •Networks: highway on which data can travel •Internet: Network of networks

1.3 1-1 DATA COMMUNICATIONS 1-1 DATA COMMUNICATIONS • The term The term telecommunication telecommunication ( (includes telephony, telegraphy, and television) ) means communication at a distance means communication at a distance ( (tele as greek word, means far tele as greek word, means far) ). The . The word word data data refers to information presented in whatever form is refers to information presented in whatever form is agreed upon by the parties creating and using the data. agreed upon by the parties creating and using the data. • Data communications Data communications are the exchange of data between two are the exchange of data between two devices via some form of transmission medium such as a wire devices via some form of transmission medium such as a wire cable. cable. • For data communications to occur, need a comm. system need a comm. system consisting of H/W & S/W. consisting of H/W & S/W. • The effectiveness of a data communications system depends on four fundamental characteristics: 1. Delivery: Data must be received by intended device 2. Accuracy: System must deliver the data accurately 3. Timeliness: The system must deliver data in a timely manner. 4. Jitter: Uneven delay in the delivery of audio or video packets

1.4 Figure 1.1 Five components of data communication 1. Message. The message is the information (data) to be communicated, e.g., text, numbers, pictures, audio, and video. 2. Sender. The sender is the device that sends the data message, e.g., computer, workstation, telephone handset, video camera 3. Receiver. The receiver is the device that receives the message, e.g., telephone handset, television, PC. 4. Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver, e.g., twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves. 5. Protocol. A protocol is a set of rules that govern data communications. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

1.5 Figure 1.2 Data flow (simplex, half-duplex, and full-duplex) • Information today comes in different forms such as text (ascii value), numbers, images(pixels), audio (continuous signal), and video(moving image). All these forms are converted to bit patterns. Keyboards and traditional monitors are examples of simplex devices. Walkie-talkies, Entire channel is occupied by each side E.g., Telephone. Channel is divided between signals traveling in both directions.

1.6 1-2 NETWORKS 1-2 NETWORKS A A network network is a set of devices (often referred to as is a set of devices (often referred to as nodes nodes) ) connected by communication connected by communication links links. A node can be a . A node can be a computer, printer, or any other device capable of sending computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the and/or receiving data generated by other nodes on the network. Network can be characterized by: network. Network can be characterized by: • Distributed Processing: Task is divided among multiple computers to share load and speedup computation • Network Criteria: Performance (transit and response time, throughput and delay), reliability (frequency of failure), and security (data protection). • Physical Structures: Discuss link types and topologies (mesh, star, bus, and ring) • Network Models: OSI and network models • Categories of Networks: Local-area networks and wide-area networks. • Interconnection of Networks: Internetwork

1.7 Figure 1.3 Types of connections: point-to-point and multipoint A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. A link can be:

1.8 Figure 1.4 Categories of topology

1.9 Figure 1.5 A fully connected mesh topology (five devices) • n(n -1) /2 full duplex links are needed to connect n nodes • To accommodate that many links, every device on the network must have n -1 input/output ports, Advantages: 1.Dedicated link 2.Robustness 3.Privacy • The main disadvantages of a mesh are related to the amount of cabling and the number of I/O ports required.

1.10 Figure 1.6 A star topology connecting four stations • Each device has a dedicated point-to-point link, only to a central controller, usually called a hub. • No direct traffic among devices, hub acts as an exchange. Less expensive and robust architecture • Disadvantage: dependence on hub

1.11 Figure 1.7 A bus topology connecting three stations Nodes are connected to the bus cable by drop lines and taps. However, a fault or break in the bus cable stops all transmission

1.12 Figure 1.8 A ring topology connecting six stations • Dedicated point-to-point connection between 2 devices. Each device in the ring incorporates a repeater which regenerates the bits and passes to next device • A ring is relatively easy to install and reconfigure. • The only constraints are media and traffic considerations (maximum ring length and number of devices) • If device does not receive a signal within a specified period, it can issue an alarm which alerts the operator. • Ring topology was prevalent when IBM introduced its local-area network.

1.13 Figure 1.9 A hybrid topology: a star backbone with three bus networks • A network can be hybrid. For example, we can have a main star topology with each branch connecting several stations in a bus topology

1.14 Network Types • A network can be a • LAN • WAN • Switched: Circuit or Packet • Internet: composed of thousands of interconnected networks

1.16 Figure 1.11 WANs: a switched WAN and a point-to-point WAN Switched WAN connects the end systems, which usually comprise a router using X.25 (ATM) or frame relay. Point-to-point WAN is normally a line leased from a telephone or cable TV provider that connects a home computer or a small LAN to an Internet service provider (lSP).

1.17 Figure 1.11 Switched Networks • Efficient when it is being utilized at full capacity. • A router in a packet- switched network has a queue that can store and forward the packet. • Delay types

1.18 Figure 1.12 A heterogeneous network made of four WANs and two LANs Interconnection of Networks • Today, it is very rare to see a LAN or a WAN in isolation; they are connected to one another. • When two or more networks are connected, they make an internetwork, or internet.

1.19 1-3 THE INTERNET 1-3 THE INTERNET The The Internet Internet has revolutionized many aspects of our daily has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a way we spend our leisure time. The Internet is a communication system that has brought a wealth of communication system that has brought a wealth of information to our fingertips and organized it for our use. information to our fingertips and organized it for our use. A Brief History: •There were some communication networks, such as telegraph and telephone networks, before 1960. These networks were suitable for constant-rate communication after a connection establishment between two users, in the form of encoded message (telegraphy) or voice (telephony). •Needed packet switched network (PSN) to support bursty traffic. PSN presented in 1961 •ARPA in DoD in 1967 developed ARPANET •Idea of communication between different networks in 1972. •TCPIP in 1973 •The Internet Today (ISPs)

1.20 Figure 1.13 Hierarchical organization of the Internet

1.21 Assignment # 1 Assignment # 1 Discuss the history and evolution of Internet. Due Date: Next Week 2nd Class

Lecture of computer communication and networks chapter 1

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