1.1 Introduction

DATA COMMUNICATIONS The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data. Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Components Data Representation Data Flow Topics discussed in this section:

1.3 The effectiveness of a data communication depends on three fundamental characteristics Delivery : The system must deliver data to the correct destination. Accuracy : The system must deliver data accurately. Timeliness : The system must deliver data in a timely manner. Data deliver late are useless.

1.4 Figure 1.1 Five components of data communication

1.5 Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

NETWORKS A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. Distributed Processing Network Criteria Physical Structures Network Models Categories of Networks Interconnection of Networks: Internetwork Topics discussed in this section:

1.7 Distributed Processing Networks use Distributed Processing, in which a task is divided among multiple computers

1.8 Advantages of distributed processing Security/encapsulation: Distributed database: Faster Problem solving: Security through redundancy: Collaborative Processing:

1.9 Network Criteria A Network must meet a number of Criteria Performance Reliability security

1.10

1.11 Performance Number of Users : Having a large number of concurrent users can slow response time in a network Type of transmission medium : The medium defines the speed at which data can travel through a connection (data rate). Hardware : The types of hardware included in a network affect both the speed and capacity of transmission. Software : The software used to process data at the sender, receiver, and intermediate nodes also affects network performance.

1.12 Reliability Frequency of failure : All networks fail occasionally. A network that fails often, however, is of little value to a user. Recover time of a network after a failure : How long does it take to restore service? Catastrophe : Networks must be protected from catastrophic events such as,fire, earthquake.

1.13 Security Unauthorized access : Passwords, encryption techniques. Viruses

1.14 Figure 1.3 Types of connections: point-to-point and multipoint

1.15 Figure 1.4 Categories of topology

1.16 Figure 1.5 A fully connected mesh topology (five devices)

1.17 Figure 1.6 A star topology connecting four stations

1.18 Figure 1.7 A bus topology connecting three stations

1.19 Figure 1.8 A ring topology connecting six stations

1.20 Figure 1.9 A hybrid topology: a star backbone with three bus networks

1.21 Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

1.22 Figure 1.11 WANs: a switched WAN and a point-to-point WAN

1.23 Figure 1.12 A heterogeneous network made of four WANs and two LANs

THE INTERNET The Internet has revolutionized many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use. A Brief History The Internet Today (ISPs) Topics discussed in this section:

1.25 Figure 1.13 Hierarchical organization of the Internet

PROTOCOLS AND STANDARDS In this section, we define two widely used terms: protocols and standards. First, we define protocol, which is synonymous with rule. Then we discuss standards, which are agreed-upon rules. Protocols Standards Standards Organizations Internet Standards Topics discussed in this section:

1.27 Protocols and Standards Protocols: is a set of rules that govern data communication. A protocol defines what is communicated, how is communicated, and when it is communicated.

1.28 Protocols key elements Syntax : Structure or format of the data. Semantics : meaning of each section of bits. Timing : when data should be sent and how fast they can be sent

1.29 Standards A standard provides a model for development that makes it possible for a product to work regardless of the individual manufacturer.

1.30 Standards De facto (by fact) De jure (by law) e.g. TCP/ IPe.g. OSI

1.31 Standards Organizations Internet Society ISO ITU-T (formally CCITT) ATM forum

1.32 Standard Organizations Standards are developed by cooperation among standards creation committees forums.