1.1 Chapter 1 Introduction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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 communications system depends on Four fundamental characteristics: Delivery Accuracy Timeliness Jitter

Components

1.5 Data Representation Data TextNumbersImageAudioVideo

1.6 Data Flow

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:

1.8 Distributed Processing  Most networks use distributed processing in which a task is divided among multiple computers.  Instead of one single large machine being responsible for all aspects of a process, separate computers handle a subset.

1.9 Network Criteria  Performance - Measured in many ways, including transit time and response time. - The performance of a network depends on a number of factors, Including number of users, type of transmission medium, capabilities of the connected hardware, and the efficiency of the software. -Performance are usually evaluated by two networks metrics: Throughput and Delay.  Reliability Measured by the frequency of failure, the time it takes a link to recover from failure.  Security Include protecting data from unauthorized access, from damages, and implementing policies and procedures for recovery from data looses.

1.10 Detected Links between two devices Entire capacity is reserved for transmission between two devices Could be wired or wireless Physical Structure Type of connection a) Point-to-point (P2P)

1.11 More than two devices share a single link. The capacity of the channel is shared (spatially/temporally) Physical Structure Type of connection a) Multipoint

1.12 Physical Structure Physical Topology

1.13 Physical Structure Physical Topology a) Mesh Dedicated p2p Number of links depends on duplex mode Advantages - no traffic problems - it is robust - privacy - fault isolation Disadvantages - wiring - I/O requirements

1.14 Devices are connected through a hub (p2p) No direct traffic between devices Advantages - less wiring - fault isolation Disadvantages - centralized - traffic Physical Structure Physical Topology b) Star

1.15 Point to multipoint Advantages: - easy to install. - cheap Disadvantages: - no fault isolation. - limited. - quality due to connectors - fault can cause noise - congestion Physical Structure Physical Topology c) Bus

1.16 Point to point every device is connected to its neighbor on either sides Repeater is used simple/dual ring Token ring (no collision) Advantages: (easy to install/ fault isolation (alarm)) Disadvantages: (no fault isolation/ limited/ quality due to connectors/ fault can cause noise/ congestion) Physical Structure Physical Topology d) Ring

1.17 Physical Structure Physical Topology e) Hybrid

1.18 Network Model  Computer networks are created by different entities.  Standards are needed so that these heterogeneous networks can communicate with one another.  The two best-known standards are OSI model and the Internet model.

1.19 Categories on Network  LAN networks connect a single office, building, campus  WAN network connect countries, the world  MAN network connect areas inside cities

1.20 LAN size is limited to few km Used to share resources usually server based Categories on Network LAN

1.21 Provide long distance transmission Internet is example Switched/p2p X.25/ATM WiMax Categories on Network WAN

1.22 Categories on Network MAN A metropolitan area network (MAN) is a network with a size between a LAN and a WAN. It normally covers the area inside a town or a city A good example of a MAN is the part of the telephone company network that can provide a high-speed DSL line to the customer.

1.23 When 2 or more network connected together it becomes an internetwork or internet Interconnection of Network: Internetwork

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.  The Internet is a structured, organized system. A Brief History The Internet Today (ISPs) Topics discussed in this section:

1.25 A Brief History  A network is a group of connected communicating devices.  An internet is two or more networks communicate together.  The most notable internet is called (Internet).  In 1960, mainframes was standalone devices, the Advanced Research Project Agency (ARPA) start the first computer connection.  In 1967, at ACM, ARPA presents ARPANET.  In 1969, reality of ARPANET.  In 1972, Vint Cerf and Bob Kahn produced the Internet Project.  TCP splitted into two protocols: TCP and IP.

1.26 The Internet Today

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:

1.28 Protocols A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key elements of a protocol are syntax, semantics, and timing. Syntax refers to the structure or format of the data, meaning the order in which they are presented. Semantics. The word semantics refers to the meaning of each section of bits. How is a particular pattern to be interpreted, and what action is to be taken based on that interpretation? Timing. The term timing refers to two characteristics: when data should be sent and how fast they can be sent.

1.29 Standards Standards are essential in guaranteeing national and international interoperability of data and telecommunications technology and processes. Standards provide guidelines De facto standards -> by manufacturers De jure standards -> by government

1.30 Standards Organization Standard Creation Committee International Organization for Standardization (ISO). International Telecommunication Union – Telecommunication Standard Sectors (ITU-T). American National Standard Institute (ANSI). Institute of Electrical and Electronic Engineers (IEEE). Electronic Industries Association (EIA).

1.31 Internet Standards It is a thoroughly tested specification that is useful to and adhered to by those who work with the Internet. There is a strict procedure by which a specification attains Internet standard status. An Internet Draft is a working document with no official status. A draft may be published as a Request for Comment (RFC).