ASSINGNMENT CHAPTER 10 from Mr. Tri Djoko Wahjono,Ir, M.Sc

ASSINGNMENT CHAPTER 10

Chapter Review Pages 542 – 543

Discovering Computer (“Living In the Digital World 2011”)

Lecture       :         Mr. Tri Djoko Wahjono,Ir, M.Sc

Student      :        Williem [1701309721]

1.      What Is a Database, and How Does a database interact with Data and Information?

A database is a collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system or data base is a collection of data organized in a manner that allows access, retrieval, and use of that data.

To access information from a database, you need a database management system (DBMS). This is a collection of programs that enables you to enter, organize, and select data in a database. Database management system (DBMS) is a software system designed to allow the definition, creation, querying, update, and administration of databases. Database software, often called a database management system (DBMS), allows users to create a computerized database; add, modify, and delete the data; sort and retrieve the data; and create forms and reports from the data. Data is a collection of unprocessed items, which can include text, numbers, images, audio, and video. Computers process data into information. Information is processed data; that is, it is organized, meaningful, and useful. In addition to documents, information can be in the form of audio, images, and video.

2.      What Is Data Integrity, and What Are the Qualities of Valuable Information?

Data integrity refers to maintaining and assuring the accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes or retrieves data. Data integrity identifies the quality of data. Data integrity is important because computers and people use information to make decisions and take actions. For a computer to produce correct information, the data that is entered in a database must have integrity.

For information to be valuable, it should be:

·         Accurate information

Accurate information is error free. Inaccurate information can lead to incorrect decisions.

·         Verifiable information

Verifiable information can be proven as correct or incorrect.

·         Timely

                       Timely information has an age suited to its use.

·         Organize

Organized information is arranged to suit the needs and requirements of the decision maker.

·         Accessible

 Accessible information is available when the decision maker needs it.

·         Useful

Useful information has meaning to the person who receives it.

·         Cost-effective

      Cost-effective information should give more value than it costs to produce.

3.       What Is Meant by Character, Field, Record, and File?

·         Character

A bit is the smallest unit of data the computer can process. Eight bits grouped together in a unit comprise a byte. In the ASCII coding scheme, each byte represents a single character, which can be a number (4), letter (R), space, punctuation mark (?), or other symbol (&). The Unicode coding scheme, by contrast, uses one or two bytes to represent a character

·         Field is combination of one or more characters, field is the basic data entry in a record. A field is a combination of one or more related characters or bytes and is the smallest unit of data a user accesses

·         Record is a row of data added to this table. A record is a group of related fields.

·         A data file is a collection of related records stored on a storage medium such as hard disk or optical disc.

4.      What Are File Maintenance Techniques and Validation Techniques?

·         File Maintenance

Refers to the procedures that keep data current. File maintenance procedures include adding records to correct inaccurate data or to update old data with new data, and deleting records when they no longer are needed

·         Validation

Validation is the process of comparing data with a set of rules or values to find out if the data is correct. Many programs perform a validity check that analyzes data, either as you enter it or after you enter it, to help ensure that it is correct. Types of validity checks include an alphabetic check, a numeric check, a range check, a consistency check, a completeness check, and a check digit.

5.      How Is a File Processing Approach Different from the Database Approach?

·         In simple term, a file processing system coordinates only physical access to data. A database organizes and coordinate both physical and logical data access.

·         In file processing data redundancy—same fields stored in multiple file but in Database Approach Reduced data redundancy.

·         In isolated data—data stored in separate files so it is difficult to access but in Database Approach not difficult to access.

·         A database specifically reduces the amount of duplication of data in a system. Additionally, since a database is designed to allow access queries where a file system only allows pre-determined data access, database queries can be far more refined and flexible, as well as granting user access privileges data.

·         Databases, unlike file processing systems, allow multiple protect stored users to access the same data simultaneously. File processing systems are far more restricted on this level.

·         The database's far easier to enforce uniform standards over the data because data can be formatted to fit a particular screen, allowing a single type of data file to be created across the system for example.

·         Database applications are quicker and easier to develop due to standardized components.

·         Due to design, databases are far more flexible as well. They can be adapted far more easily to cope with changing situations than a file processing system.

·         The economy of implementing a database across a huge network is greater than implementing a full file processing system.

·         Databases are essentially easy to install, and are far more user friendly.

·         In a file processing system, each department or area within an organization has its own set of data files. The records in one file may not relate to the records in any other file. Two major weak- nesses of fi le processing systems are redundant data (duplicated data) and isolated data.

·         With a database approach, many programs and users share the data in a database. The database approach reduces data redundancy, improves data integrity, shares data, permits easier access, and reduces development time. A database, however, can be more complex than a file processing system, requiring special training and more computer memory, storage, and processing power than file processing systems.

·         Data in a database also can be more vulnerable than data in file processing systems.

6.      What Functions Are Common to Most Database Management Systems?

a.      The ability to update and retrieve data

This is a fundamental component of a DBMS and essential to database management. Without the ability to view or manipulate data, there would be no point to using a database system.

Updating data in a database includes adding new records, deleting existing records and changing information within a record. The user does not need to be aware of how DBMS structures this data, all the user needs to be aware of is the availability of updating and/or pulling up information, the DBMS handles the processes and the structure of the data on a disk.

b.      Support Concurrent Updates

Concurrent updates occur when multiple users make updates to the database simultaneously. Supporting concurrent updates is also crucial to database management as this component ensures that updates are made correctly and the end result is accurate. Without DBMS intervention, important data could be lost and/or inaccurate data stored.

DBMS uses features to support concurrent updates such as batch processing, locking, two-phase locking, and time stamping to help make certain that updates are done accurately. Again, the user is not aware all this is happening as it is the database management system’s responsibility to make sure all updates are stored properly.

c.       Recovery of Data

In the event a catastrophe occurs, DBMS must provide ways to recover a database so that data is not permanently lost. There are times computers may crash, a fire or other natural disaster may occur, or a user may enter incorrect information invalidating or making records inconsistent.

If the database is destroyed or damaged in any way, the DBMS must be able to recover the correct state of the database, and this process is called Recovery. The easiest way to do this is to make regular backups of information. This can be done at a set structured time so in the event a disaster occurs, the database can be restored to the state that it was last at prior to backup. Backup and recovery is brought to mind whenever there is potential outside threats to a database. For example if there is a power outage, recovery management is how long it takes to recover the database after the outage. Backup management refers to the data safety and integrity; for example backing up all your mp3 files on a disk.

A disadvantage to this is any data or changes entered after the backup would be lost. A way to counteract this is to set the DBMS to provide a feature called Journaling. This involves keeping a log of all updates made to the database, it is maintained in a file separate from the database and can be obtained to re-update the database after it is recovered from the backup.

d.      Security

Security is the prevention of unauthorized users accessing the database. DBMS uses features such as encryption, authentication, authorization and views to provide security to the database. Encryption is when DBMS converts the data in a database to an indecipherable format. No unauthorized person trying to access this information will be able to read it. Authorized users will be able to see it in normal form.

Authentication is a technique in which the database administrator can identify the person accessing the database. Authorized users are given passwords and successful entry of a valid password will allow the user entry into the database, if a password is not successfully entered, the user will be denied access. Authorization is a set of rules that the database administrator (DBA) sets up to specify levels of usage that individuals or groups are allowed to have. Some users may only be allowed viewing options, while others may be allowed to both view/make changes.

In some circumstances, users may only be allowed to access certain pieces of the database, and be denied access to areas that does not relate to their specific needs. In these cases, the DBA will assign workgroups, and these workgroups will be assigned levels of access and permissions. Views are when DBA allows certain users the ability to view the tables or fields that pertain to them, any other view does not exist for them in the database, DBMS does this behind the scenes and to the user it appears that the information they see are the only existing data.

e.       Data Integrity

Data integrity is an important function in database management. This is a set of rules that DBMS provides to see that data integrity is enforced, thus avoiding incorrect or inconsistent data. Types of integrity that DBMS provides are data type, legal values and format. Key integrity also falls into this function of DBMS. This enforces that the primary key of a record remains unique.

7.      What Are Characteristics of Relational, Object-Oriented, and Multidimensional Databases?

A.    Relational Data Base

a.       Stores data in tables that consist of rows and columns

b.      Each row has primary key

c.       Each column has unique name

d.      Stores data relationships

e.       Uses specialized terminology

to a file as a table, a record as a row, and a field as a column. A relationship is a link within the data in a relational database. Structured Query Language (SQL) allows users to manage, update, and retrieve data in a relational database.

B.     An Object-Oriented Database (OODB)

a.       Stores data in objects. An object is an item that contains data, as well as the actions that read or process the data.

b.      Advantages

c.       Can store more types of data

d.      Can access data faster

e.       Often uses object query language (OQL)

f.       Object-oriented databases often use an object query language (OQL) to manipulate and retrieve data.

g.      Applications appropriate for an object-oriented database include a multimedia database, a groupware database, a computer-aided design (CAD) database, a hypertext database, and a hypermedia database.

C.    A Multidimensional Database

a.       Stores data in dimensions.

b.      These multiple dimensions, sometimes known as a hypercube, allow users to access and analyze any view of the database data.

c.       No standard query language exists for multidimensional databases.

d.      One application that uses multidimensional databases is a data warehouse, which is a huge database that stores and manages the data required to analyze historical and current transactions.

e.       A smaller version of a data warehouse is the data mart, which contains a database that helps a specific group or department make decisions.

f.       Multiple dimensions, also called hypercube, allow users to analyze any view of data

g.      Can consolidate data much faster than relational database

8.      How Are Web Databases Accessed?

Database you access through the Web by filling in a form on a Web page usually resides on a database server, a computer that stores and provides access to a database. To access data in a Web database, you fill in a form or enter search text on a Web page, which is the front end to the database. A Web database usually resides on a database server, which is a computer that stores and provides access to a database. One type of program that manages the sending and receiving of data between the front end and the database server is a CGI (Common Gateway Interface) script.

9.      What Are the Responsibilities of Database Analysts and Administrators?

·         A database analyst (DA), or data modeler,

a.       Focuses on the meaning and usage of data.

b.      The DA decides on the placement of fields, defines data relationships, and identifies users’ access privileges.

·          A database administrator (DBA) requires a more technical inside view of the data. In small companies, one person often is both the DA and DBA. In larger companies, the responsibilities of the DA and DBA are split among two or more people.

The DBA is an IT Professional that take care about

A.    Installation

To install a program to the company computer.

B.     Configuration

C.     Upgrade

Checks backup and recovery procedures.

D.    Administration

E.     Monitoring

Monitors database performance

F.      Maintenance

The DBA creates and maintains the data dictionary

G.    Securing

Manages database security

ASSINGNMENT CHAPTER 9 from Mr. Tri Djoko Wahjono Ir, M.Sc

    

ASSINGNMENT CHAPTER 9

Chapter Review 

Discovering Computer (“Living In the Digital World 2011”)

Lecture       :        Mr. Tri Djoko Wahjono Ir, M.Sc

Student      :        Williem [1701309721]

         1.  What Is the Purpose of the Components Required for Successful Communications, and What Are Various Sending and Receiving Devices?

Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information. Today, even the smallest computers and devices can communicate directly with one another, with hundreds of computers on a company network, or with millions of other computers.

For successful communications, you need the following:

v  A sending device that initiates an instruction to transmit data, instructions, or information.

v  A communications device that connects the sending device to a communications channel.

v  A communications channel, or transmission media on which the data, instructions, or information travel.

v  A communications device that connects the communications channel to a receiving device.

v  A receiving device that accepts the transmission of data, instructions, or information.

Some devices that serve as sending devices and receiving devices are

a)    mainframe computers,

b)   servers,

c)    desktop computers,

d)   notebook computers,

e)   smart phones,

f)    Internet-enabled portable media players,

g)   handheld game consoles, and

h)   GPS receivers.

The communications channel consists of telephone and power lines, cable television and other underground lines, microwave stations, and satellites.

        2.  How Are Computer Communications Used?

Computer communications are everywhere. Many require that users subscribe to an Internet access provider. With other computer communications, an organization such as a business or school provides communications services to employees, students, or customers.

The following pages discuss a variety of computer communications. Communications technologies include blogs, chat rooms, e-mail, fax, FTP, instant messaging, newsgroups, RSS, video conferencing, VoIP, Web, Web folders, and wikis. Users can send and receive wireless messages to and from smart phones, cell phones, handheld game consoles, and other mobile devices using text messaging, picture messaging and video messaging, and wireless instant messaging. People connect wirelessly to the Internet through a wireless Internet access point. A hot spot is a wireless network that provides Internet connections to mobile computers and devices. A cybercafé is a coffeehouse, restaurant, or other location that provides computers with Internet access. A global positioning system (GPS) analyzes signals sent by satellites to determine an earth-based receiver’s geographic location. Many software products provide a means to collaborate, or work online with other users connected to a server. Groupware is software that helps groups of people work on projects or share information over a network.

Voice mail allows someone to leave a voice message for one or more people. Web services describe standardized software that enables programmers to create applications that communicate with other remote computers.

       3.  What Are the Advantages of Using a Network, and How Are LANs, MANs, and WANs Different?

a network is a collection of computers and devices  connected together via communications devices and transmission media. Many businesses network their computers together to facilitate communications, share hardware, share data and information, share software, and transfer funds.

o   Facilitating communications — Using a network, people communicate efficiently and easily via e-mail, instant messaging, chat rooms, blogs, wikis, online social networks, video telephone calls, online meetings, video conferencing, VoIP, wireless messaging services, and groupware.

o   Sharing hardware — In a networked environment, each computer on the network can have access to hardware on the network. Business and home users network their hardware to save money.

o   Sharing data and information — In a networked environment, any authorized computer user can access data and information stored on other computers on the network.

o   Sharing software — Users connected to a network have access to software on the network.

v  To support multiple users’ access of software, most vendors sell network versions or site licenses of their software, which usually cost less than buying individual copies of the software for each computer.

o   Transferring funds — Called electronic funds transfer (EFT ), it allows users connected to a network to transfer money from one bank account to another via transmission media.

LANs, MANs, and WANs

Networks usually are classified as a local area network, metropolitan area network, or wide area network. The main differentiation among these classifications is their area of coverage.

·         LAN (local area network) is a network that connects computers and devices in a limited geographical area such as a home, school computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network, called a node, often shares resources such as printers, large hard disks, and programs.Often, the nodes are connected via cables.

·         MAN (metropolitan area network) is a high-speed network that connects local area networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. A MAN typically includes one or more LANs, but covers a smaller geographic area than a WAN. A MAN usually is managed by a consortium of users or by a single network provider that sells the service to the users. Local and state governments, for example, regulate some MANs. Telephone companies, cable television operators, and other organizations provide users with connections to the MAN.

·         WAN (wide area network) is a network that covers a large geographic area (such as a city, country, or the world) using a communications channel that combines many types of media such as telephone lines, cables, and radio waves (Figure 9-12). A WAN can be one large network or can consist of two or more LANs connected together. The Internet is the world’s largest WAN.

         4.  How Are a Client/Server and Peer-to-Peer Network Different, and How Does a P2P Network Work?

·         Client/Server

On a client/server network, one or more computers act as a server, and the other computers on the network request services from the server. A server, sometimes called a host computer, controls access to the hardware, software, and other resources on the network and provides a centralized storage area for programs, data, and information. The clients are other computers and mobile devices on the network that rely on the server for its resources. For example, a server might store a database of customers. Clients on the network (company employees) access the customer database on the server.

·         Peer-to-Peer

One type of peer-to-peer network is a simple, inexpensive network that typically connects fewer than 10 computers. Each computer, called a peer, has equal responsibilities and capabilities, sharing hardware (such as a printer), data, or information with other computers on the peer-to-peer network. Each computer stores files on its own storage devices. Thus, each computer on the network contains both the server operating system and application software. All computers on the network share any peripheral device(s).attached to any computer. For example, one computer may have a laser printer and a scanner, while another has an ink-jet printer and an external hard disk. Peer-to-peer networks are ideal for very small businesses and home users.

·         Another type of peer-to-peer, called P2P, describes an Internet network on which users access each other’s hard disks and exchange files directly over the Internet. This type of peer-to peer network sometimes is called a file sharing network because users with compatible software and an Internet connection copy files from someone else’s hard disk to their hard disks. As more users connect to the network, each user has access to shared files on other users’ hard disks. When users log off the network, others no longer have access to their hard disks.

         5.  How Are a Star Network, Bus Network, and Ring Network Different?

 ·         Star Network

On a star network, all of the computers and devices (nodes) on the network connect to a central device, thus forming a star. Two types of devices that provide a common central connection point for nodes on the network are a hub and a switch. All data that transfers from one node to another passes through the hub or switch. Star networks are fairly easy to install and maintain. Nodes can be added to and removed from the network with little or no disruption to the network. On a star network, if one node fails, only that node is affected. The other nodes continue to operate normally. If the hub or switch fails, however, the entire network is inoperable until the device is repaired. Most large star networks, therefore, keep backup hubs or switches available in case the primary one fails.

·         Bus Network

A bus network consists of a single central cable, to which all computers and other devices connect. The bus is the physical cable that connects the computers and other devices. The bus in a bus network transmits data, instructions, and information in both directions. When a sending device transmits data, the address of the receiving device is included with the transmission so that the data is routed to the appropriate receiving device. Bus networks are popular on LANs because they are inexpensive and easy to install. One advantage of the bus network is that computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network.

·         Ring Network

On a ring network, a cable forms a closed loop (ring) with all computers and devices arranged along the ring. Data transmitted on a ring network travels from device to device around the entire ring, in one direction. When a computer or device sends data, the data travels to each computer on the ring until it reaches its destination. If a computer or device on a ring network fails, the entire network potentially could stop functioning. A ring network can span a larger distance than a bus network, but it is more difficult to install. The ring topology primarily is used for LANs, but also is used in WANs.

        6.  What Are Various Network Communications Standards?

A network standard defines guidelines that specify the way computers access a medium, the type(s) of medium, the speeds on different types of networks, and the type of physical cable or wireless technology used. Network communications standards include the following. Ethernet specifies that no central computer or device on the network should control when data can be transmitted. Token ring requires devices to share or pass a special signal, called a token. TCP/IP divides data into packets. Wi-Fi identifies any network based on the 802.11 standards for wireless communications.  Bluetooth uses short-range radio waves to transmit data. UWB specifies how two UWB devices use short-range radio waves to communicate at high speeds. IrDA transmits data wirelessly via infrared light waves. RFID uses radio signals for communications. WiMAX is a network standard developed by IEEE that specifies how wireless devices communicate over the air in a wide area. The Wireless Application Protocol (WAP) specifies how some mobile devices can display Internet content.

           7.    What Is the Purpose of Communications Software?

Communications software consists of programs that 

(1) help users establish a connection to another computer or network; 

(2) manage the transmission of data, instructions, and information; and

 (3) provide an interface for users to communicate with one another. The first two are s

ystem software and the third is application software. Chapter 3 presented a variety of examples of application software for communications: e-mail, FTP, Web browser, newsgroup/message boards, chat rooms, instant messaging, video conferencing, and VoIP. Sometimes, communications devices are preprogrammed to accomplish communications tasks. Other communications devices require separate communications software to ensure proper transmission of data. Communications software works with the network standards and protocols just discussed to ensure data moves through the network or the Internet correctly. Communications software usually is bundled with the operating system or purchased network devices. Communications software helps users establish a connection to another computer or network; manages the transmission of data, instructions, and information; and  provides an interface for users to communicate with one another.

      8.  What Are Various Types of Lines for Communications over the Telephone Network?

·         Dial-Up Lines

A dial-up line is a temporary connection that uses one or more analog telephone lines for communications. A dial-up connection is not permanent. a dial-up line to connect computers costs no more than making a regular telephone call.

·         Dedicated Lines

Satellite local access area local telephone company A dedicated line is a type of always on connection that is established between two communications devices (unlike a dial-up line where the connection is reestablished each time it is used). The quality and consistency of the  connection on a dedicated line are better than a dial-up line because dedicated lines provide a constant connection. Businesses often use dedicated lines to connect geographically distant offices. Dedicated lines can be either analog or digital. Digital lines increasingly are connecting home and business users to networks around the globe because they transmit data and information at faster rates than analog lines. Five types of digital dedicated lines are ISDN lines, DSL, FTTP, T-carrier lines, and ATM.

·         ISDN Lines

For the small business and home user, an ISDN line provides faster transfer rates than dial-up telephone lines. Not as widely used today as in the past, ISDN (Integrated Services Digital Network) is a set of standards for digital transmission of data over standard copper telephone lines. With ISDN, the same telephone line that could carry only one computer signal now can carry three or more signals at once through the same line, using a technique called multiplexing.

·         DSL

DSL is a popular digital line alternative for the small business or home user. DSL (Digital Subscriber Line) transmits at fast speeds on existing standard copper telephone wiring.

Some DSL installations include a dial tone, providing users with both voice and data communications. These DSL installations often require that filters be installed to reduce noise interference when voice communications share the same line. ADSL is one of the more popular types of DSLs. As shown in Figure 9-25, ADSL (asymmetric digital subscriber line) is a type of DSL that supports faster transfer rates when receiving data (the downstream rate) than when sending data (the upstream rate). ADSL is ideal for Internet access because most users download more information from the Internet than they upload.

·         FTTP

FTTP, which stands for Fiber to the Premises, uses fiber-optic cable to provide extremely high-speed Internet access to a user’s physical permanent location. Two specific types of FTTP are FTTH and FTTB. FTTH (Fiber to the Home) provides home users with Internet access via fiber-optic cable. Similarly, FTTB (Fiber to the Building) refers to small businesses that use fiber-optic cables to access the Internet. With FTTP service, an optical terminal at your location receives the signals and transfers them to a router connected to your computer. As the cost of installing fiber decreases, more homes and businesses will opt for this high-speed Internet access.

·         T-Carrier Lines

A T-carrier line is any of several types of long-distance digital telephone lines that carry multiple signals over a single communications line. Where as a standard dial-up telephone line carries only one signal, digital T-carrier lines use multiplexing so that multiple signals share the line. T-carrier lines provide very fast data transfer rates. Only medium to large companies usually can afford the investment in T-carrier lines because these lines are so expensive.

·         ATM

ATM (Asynchronous Transfer Mode) is a service that carries voice, data, video, and multimedia at very high speeds. Telephone networks, the Internet, and other networks with large amounts of traffic use ATM. Some experts predict that ATM eventually will become the Internet standard for data transmission, replacing T3 lines.

     9.  What Are Commonly Used Communications Devices?

·         A communications device is hardware capable of transmitting data between a sending device and a receiving device.

·         A dial-up modem converts digital signals to analog signals and analog signals to digital signals. So that data can travel along analog telephone lines.

·         A digital modem sends and receives data and information to and from a digital line.

·         An ISDN modem transmits digital data to and from an ISDN line, while a DSL modem transmits digital data to and from a DSL line.

·         A cable modem, sometimes called a broadband modem, is a digital modem that sends and receives digital data over the cable television network.

·         A wireless modem uses the cell phone network to connect to the Internet wirelessly from mobile computers and devices.

·         A network card enables a computer or device that does not have built-in networking capability to access a network.

·         A wireless access point allows computers and devices to transfer data wirelessly.

·         A router connects multiple computers or other routers together and transmits data to its correct destination on the network.

·         A hub or switch is a device that provides a central point for cables in a network.

     10.            How Can a Home Network Be Set Up?

a)    A home network connects multiple computers and devices in a home.

b)   An Ethernet network connects each computer to a hub with a physical cable.

c)    A home power line cable network uses the same lines that bring electricity into the house.

d)   A phone line network uses existing telephone lines in a home. Most home networks use a Wi-Fi network.

    11.            What Are Various Physical and Wireless Transmission Media?

·         Twisted-Pair Cable

One of the more widely used transmission media for network cabling and telephone systems is twisted-pair cable. Twisted-pair cable consists of one or more twisted-pair wires bundled together. Each twisted-pair wire consists of two separate insulated copper wires that are twisted together. The wires are twisted together to reduce noise. Noise is an electrical disturbance that can degrade communications.

·         Coaxial Cable

Coaxial cable, often referred to as coax (pronounced KO-ax), consists of a single  copper wire surrounded by at least three layers: (1) an insulating material, (2) a woven or braided metal, and (3) a plastic outer coating (Figure 9-37). Cable television (CATV) network wiring often uses coaxial cable because it can be cabled over longer distances than twisted-pair cable. Most of today’s computer networks, however, do not use coaxial cable because other transmission media such as fiber-optic cable transmit signals at faster rates.

·         Fiber-Optic Cable

The core of a fiber-optic cable consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signals. Each strand, called an optical fiber, is as thin as a human hair. Inside the fiber-optic cable, an insulating glass cladding and a protective coating surround each optical fiber. Fiber-optic cables have the following advantages over cables that use wire, such as twisted-pair and coaxial cables:

o   Capability of carrying significantly more signals than wire cables

o   Faster data transmission

o   Less susceptible to noise (interference) from other devices such as a copy machine

o   Better security for signals during transmission because they are less susceptible to noise

o   Smaller size (much thinner and lighter weight)

•     Broadcast radio distributes radio signals through the air over long and short distances.
•   Cellular radio is a form of broadcast radio that is used widely for mobile communications.
•  Microwaves are radio waves that provide a high speed signal transmission.
• §  A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area.