1

ITC242 – Introduction to Data Communications

2

Contact Details

• Dr Xiaodi Huang

• Building 760 Room 105

• Phone 02 60519 652

• Email xhuang@csu.edu.au

• Consultation Times– Mondays 10am – 1pm– Thursdays 10am – 1pm

3

Housekeeping

• Assignments– 1st Assignment Due 22st August– 2nd Assignment Due 17th October

• Assessment– 1st Assignment 20%– 2nd Assignment 20%– Exam 60%

• In order to pass this subject you must achieve 50% or greater in the exam, and 50% or greater as a combined assignment total.

4

Housekeeping

• Textbook:Stallings, W 2005, Business data

communications, 5th edn, Pearson Prentice Hall, Upper Saddle River, NJ.

• Web Resources– http://csusap.csu.edu.au/~xhuang/ITC242/– Textbook Web Site

• http://WilliamStallings.com/BDC/BDC5e.html• http://WilliamStallings.com/StudentSupport.html

5

Aims and objectives of the subject

Upon completion of this subject students should be able to:

1. Outline the basics components of a computer network using both the OSI model and the TCP/IP reference model;

2. Describe the nature of business information requirements and the impact on data communications;

3. Outline the modes of distributed data processing;

6

Aims and objectives of the subject

4. Enumerate the various transmission media commonly used in carrier systems;

5. Recognize and discuss the basics of data communications;

6. Enumerate the differences between wireless telephone systems;

7. Describe how to identify a satellite system and define its characteristics and use;

7

Aims and objectives of the subject

8. Document the characteristics of local area networks;

9. Identify the basics and compare and contrast characteristics of WAN technologies;

10.Describe the operation and components of the internet and internet based applications; and

11. Identify and describe the current data communication standards available.

8

Topic 1

Learning Objectives• understand the business requirements

for data communications and the broad factors influencing trends in data communications;

• describe the nature of business information requirements; and

• describe at a simple level, the different types of networks.

9

Topic 1

Activities

• Read all of Chapter 1 from the text.

• Attempt to answer Review questions 1.1, 1.2 and 1.4 from the text.

10

Communications Technology

List the communications technology you have used

•This week ?

What are the applications you have used on the Internet?

11

Data Communication System

12

Basic Components • Medium

– The data communication medium is the physical path along which data travels to its destination. It can be a guided medium such as twisted-pair cable, coaxial cable, and fiber-optic cable. Or the medium can be unguided, for example laser, radio waves, and satellite microwaves.

• Message – The message is the information that needs to be communicated. It can be audio,

text, or visual information, or any combination of these. • Protocol

– The protocol is a set of rules that provides agreement between communicating devices so that they can understand one another. As with grammar in human languages, having standard rules aids communication between participants who know them.

• Receiver – The receiver can be any network device to which data is sent. For example, a

receiver could be a computer, a telephone, a router, or a television. • Sender

– The sender can be any network device that sends a data message. For example, a sender could be a computer, a telephone, or a router.

13

Core network components A network consists of two or more computers

connected together which share resources such as data, printers, and an Internet connection.

The term "networking" refers to the sharing of resources on a network.

14

• A network consists of the following three primary components.– Server – Workstation – Host

15

Server

A server is a powerful computer that provides resources to other computers on the network. Servers are often dedicated, meaning that they perform no other tasks besides their server tasks.

16

Workstation

• A workstation is any computer on a network that can request resources and is used to do work. A workstation may have multiple CPUs, making it faster and more capable than a personal computer.

Workstations and clients are different. A client is any device on a network that can request resources.

17

Host

• A host is any network device that has a Transmission Control Protocol/Internet Protocol (TCP/IP) address. Workstations and servers that have TCP/IP addresses can be considered hosts. Each host has a unique IP address.

18

• Networks can consist of a small group of computers localized to a building or they can extend over large geographic areas, as follows.– local area network

(LAN) – wide area network

(WAN)

19

local area network (LAN)

• A LAN is a network that is confined to a small geographic area – for example, within a building. Each individual computer can access data and devices anywhere on the LAN.

20

wide area network (WAN)

• A WAN is a computer network that spans a relatively wide area. A WAN consists of a system of interconnected LANs. The Internet is an example of a global WAN.

21

WANs and LANs

WANs differ from LANs in a number of ways:

• they cover greater distances than LANs

• WAN speeds are slower

• LANs primarily use private network transports while WANs can use public or private network transports

22

WANs require several core devices to function.• Routers

– Routers are used to direct traffic on a network to its correct destination. A router is connected to at least two networks, and it is located where the networks connect.

• WAN switches – WAN switches are used to logically connect routers on the WAN using virtual

circuits. • Modems

– Modems provide remote access to networks by converting digital signals to analog ones so that the data can be transmitted over analog communication facilities such as telephone lines.

23

Metropolitan area networks (MANs)

• A metropolitan area network, or MAN, is a network that covers a metropolitan area such as a city or suburban area. MANs are larger than LANs but smaller than WANs.

• A MAN is usually created when two or more LANs are connected together, offering high-speed connections.

24

Intranets and extranets

• An intranet is a private network that exists within a business. It can consist of many interlinked LANs. Only people within the company or organization can access the intranet.

The main purpose of an intranet is to share company information and resources between employees. An intranet looks like a private version of the Internet.

25

• When part of a company's intranet becomes available to customers, suppliers, or anyone outside the company, the network is known as an extranet.

Extranets use Internet Protocol (IP) and a public communication system to share part of an organization's information and resources with its customers, suppliers, or other businesses. A firewall is used to ensure security on the network.

26

Chapter 2 : Business Information

Business Data Communications, 5e

27

Analog Data• An analog signal is an electromagnetic wave that varies

in frequency over time to transmit information. It is usually represented in the form of a sine wave.

• Continuous signal • Expressed as an oscillation (sine wave format) of

frequency• Information rate and channel capacity are measured in

hertz (Hz) of bandwidth (1 Hz = 1 cycle per second).

28

Basic Analog Terms

• Wave frequency: Number of times a cycle occurs in given time period

• Wave amplitude: Height of a wave cycle

• Hertz (Hz): The number of times a wave cycle occurs in one second (commonly used measure of frequency)

29

Bandwidth

• Bandwidth is the amount of data that can be transmitted by a medium in a specified time. It is usually measured in bits per second (bps).

• The bandwidth is fixed when you use a narrowband transmission medium - copper wires - to transmit data.

• For a broadband medium such as coaxial cable, the bandwidth available can be allocated to different data transmissions.

For example, if the total bandwidth of a broadband medium is 1000 bps, this could be divided between data, voice, video, and television transmissions, allocating 250 bps to each.

30

Types of Information

• Audio

• Data

• Image

• Video

31

Understanding Audio

• What makes sound? Vibration of air

• How can we record that vibration?

• How can we convert that to an electrical signal?

32

Digital Audio

• For good representation, must sample amplitude at a rate of at least twice the maximum frequency

• Measured in samples per second, or smp/sec• Telephone quality: 8000smp/sec, each sample

using 8 bits– 8 bits * 8000smp/sec = 64kbps to transmit

• CD audio quality: 44000smp/sec, each sample using 16 bits– 16 bits * 44000smp/sec = 1.41mbps to transmit

clearly

33

Networking Implications for Voice Communication

• Requires powerful, flexible intralocation facility, and access to outside services (e.g. telcos)

• In-house alternatives– PBX– Centrex

34

Digital Data

• Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits

• Rate and capacity of a digital channel measured in bits per second (bps)

• Digital data is binary: uses 1s and 0s to represent everything

• Data encoded in strings– ASCII, IRA, UTF, etc

• Data is often redundant

35

• The discrete nature of the digital signal and its binary format transmission means that digital signals are not as vulnerable to the interference, signal loss, and noise of analog signals. As long as the stream of bits gets to its destination, it can be reconstructed into a perfect replica of the original source.

36

Data Networking Implications

• Vary significantly based on application and data types

• Response time often a key component

37

Understanding Images

• Vector graphics– Collection of straight and curved line

segments– Image described as collection of segments

• Raster graphics– Two-dimensional array of “spots” (pixels)– Also called “bitmap” image

38

39

Networking Implications for Image Data

• More pixels=better quality=larger size• More compression=reduced quality=increased

speed– “Lossy” gives from 10:1 to 20:1 compression– “Lossless” gives less than 5:1

• Format (vector vs bitmapped/raster) affects size and therefore bandwidth requirements

• Choices in imaging technology, conversion, and communication all affect end-user’s satisfaction

40

Video Communication

• Sequences of images over time• Same concept as image, but with the

dimension of time added• Significantly higher bandwidth

requirements in order to send images (frames) quickly enough

• Similarity of adjacent frames allows for high compression rates

41

Response Time

• User response time

• System response time

• Network transfer time (throughput)

42

Bandwidth Requirements

• Review Figure 2.7

• What happens when bandwidth is insufficient?

• How long does it take to become impatient?

• Is data communication ever “fast enough”?