business data communications, fourth edition chapter 2: fundamentals of data communications here,...

Business Data Communications, Fourth Edition

Chapter 2: Fundamentals of Data Communications

Here, you’ll insert a graphic from the cover. This will come much closer to the BBD.

Learning Objectives

• Explain the concepts of bit rate, baud rate, frequency, and bandwidth

• Distinguish between digital and analog signals

• Describe the purpose of a modem and define three types of modems

• Define the data codes used in data communications

Chapter 2: Fundamentals of Data Communications 2

Learning Objectives

• Describe how a telephone works

• Describe the structure of the telephone network

• Describe the telephone numbering system in the United States


Introduction

• Data is transmitted from one point to another in data communications

• Data must be in an acceptable format

• Various forms of signals are used to transmit the data

• Telephone system is examined in this chapter


Signal Representation

• Signal – electrical charges or pulses of light

• Bit rate– Bit – smallest unit of information– Binary notation (1 or 0) or (on or off)– Data codes (ways to represent characters)



• Bit rate– Byte (a character)– Bit rate (speed at which data is transmitted)– Bits per second (used to describe bit rate)



Figure 2-1. Frequency spectrum.


• Baud Rate– Baud (change in signal)– Baud rate (number of changes per second)– Voltage (+ and – charges)– Current (flow of electric charge)



• Baud Rate– Alternating current (AC) (electrical outlets)– Direct current (DC) (batteries)– Signals made up of more than 1 bit

• Dibit (signal made up of 2 bits)• Tribit (signal made up of 3 bits)• Used for transmission of large files



• Frequency– Number of times the current goes through a

cycle– Hertz (Hz) (measure of frequency)– Kilohertz (kHz) (1,000)– Megahertz (MHz) (1,000,000)– Gigahertz (GHz) (1,000,000,000)– Audio frequencies (lowest frequencies)– See Table 2-1 for list of frequencies



• Bandwidth– Range of frequencies– BW = High frequency - Low frequency– Example:

• 2,500 Hz – 200 Hz = 2,300 Hz BW

– Guardbands (prevents frequencies from interfering with each other)

– Wider bandwidth means more data can be transmitted


Digital Signals Versus Analog Signals

• Digital data– Discrete items (text, integers)

• Analog data– Continuous data (light, voice)

• Frequency modulation– Signal is changed based on the number of waves

• Process control computers– Process continuous (analog) data



• Modems– Convert digital to analog and analog to digital– MOdulator/DEModulator– Internal

• Called a “card”, PC cards for laptops

– External• Sits on the desk next to the computer• Connected by a cable



• Modems– Modem speeds

• 9600 to 56,000 bps• Table 2-2 shows modem costs

– Data compression• Transmits fewer characters, resulting in faster

transmission speeds• Example: V.42bis (32 chars. to 11 chars.)• Maximum transmission rate is called the

throughput



• Modems– Always used in pairs– Internet Service Providers

• Provide connection to users• Has a permanent Internet connection

– On-line services• America OnLine, Microsoft Network, Yahoo• Connection to Internet & other services



• Modems– Bulletin Board System – for leaving messages– Cable Modem

• Maximum speeds of 40 Mbps (compare to 56Kbps)• Higher speeds but at a higher cost than ISP

– Modem eliminator (null modem)• 50 feet or less• 1,200 to 38,400 bps

– Short-haul modem• Up to 20 miles• 1,200 to 9,600 bps depending on distance

– Fax modem• Sends fax through a computer


Data Codes

• General Description– Data codes represent

characters– Rules for converting bits to

characters– ASCII, EBCDIC, Unicode


Data Codes

• American Standard Code for Information Interchange (ASCII)– Standard ASCII – 7 bit code– Extended ASCII – 8 bit code– Special ASCII characters for data

communications – Table 2-4


Data Codes

• Extended Binary-Coded Decimal Interchange Code (EBCDIC)– 8-bit code


Data Codes

• UNICODE– 16-bit code– Supports up to 65,536 characters– Used for languages such as Chinese,

Japanese, Korean– Includes mathematical, geometric and other

symbols– Only used with OS that can display the codes


Telecommunications – Voice Communications

• Introduction– Good quality transmission medium– Telephone network components

• The Telephone– Converts human voice to electrical signal– Converters (does the conversion)– Transmitter and Receiver (both are converters)– Diaphragm vibrates to convert sound to electricity

• Telephone network supports many features



• The Telephone Network– End office (aka central office, exchange office)– Local loop (connects home to end office)– Local exchange carrier (provides dial tone)– T-Carrier Circuits (1.5Mbps rate)


rcotter

Consider including Figure 2-19 on this slide.


• Telephone calls–Local call (made within local end offices)

• Intraoffice call (same prefix)• Interoffice call (different prefix)

–Tandem office (handles calls within an area code, unit calls)

–Toll offices (handles calls to a different area code)



• The Telephone Network– Telephone lines

• Voice-grade circuits• Multiplexing used to combine many calls on a

single line (uses guardbands to separate calls)– Used by cable TV as well

– Telephone signals• Dial tone, ringing, busy, etc.• Table 2-5 shows types of signals



• Telephone Numbering Systems– Direct distance dialing (DDD)– Area codes (expansion in 1995)– Exchange codes (prefix in phone number)– Country codes (identifies other country)– 800 service (WATS, toll free)

• 888, 877, 866 are now also toll free

– 900 service (caller charged)– Dial around services (10-10-xxx numbers)


Summary

• Signals transmit information

• Data codes convert information

• Transmission speed

• Transmission capacity

• Digital versus analog data

• ASCII code, EBCDIC code, UNICODE


Summary

• Telephone network

• Quality of telephone lines

• Telephone numbering system


Communications Trailblazer

• John T. Chambers, Cisco Systems– Cisco sells routers & switches– Cisco is successful even when the economy

is on a downturn– Chambers has received many awards– Previously at Wang labs and IBM– Has open communication with employees– Promotes tremendous loyalty among

employees


Spotlight On

• Wireless Technology in Schools– Wireless technology now in grade and high

schools as well as universities– Uses

• In classroom to do research• Accessing courses on the Web• PDAs to access e-mail, Internet, other users, to

take notes

– Higher Ed – Classroom on a cart


Chapter 2 Complete

business data communications, fourth edition chapter 2: fundamentals of data communications here,...

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