CHAPTER 3 COMPUTER NETWORKS & COMMUNICATIONS

1.1 BASIC CONCEPTS OF COMPUTER NETWORKS

Definition of Computer NetworksA computer network is a collection of computers and devices connected together via communication devices and transmission media. For example it may connect computers, printers and scanners.

Definition of CommunicationCommunication describes a process in which two or more computer or devices transfer data, instructions and information.

1.2 THE IMPORTANCE/ADVANTAGES OF COMPUTER NETWORKS

i. Sharing of devices such as printer and scannerii. Sharing of program/softwareiii. Sharing of filesiv. Sharing of datav. Sharing of informationvi. Sharing of single high-speed internet connectionvii. Can access server centered databaseviii. Better communication using Internet services such as

e-mail, mailing list and Internet Relay Chat(IRC)

Types of computer network

LAN MAN WAN

Network Architecture

Client/server Peer to peer

Types of computer network

Bus Star Ring

Network communications technology

Intranet Extranet Internet

1.3 TYPES OF COMPUTER NETWORKS

Local Area Network (LAN)

A 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.

Metropolitan Area Network (MAN)

A metropolitan area network (MAN) is a high speed network that connects local area networks in a metropolitan area such as city or town and handles bulk of communications activity across the region.

A MAN typically includes one or more LAN but covers a smaller geographic area than a WAN.

Wide Area Network (WAN)

A wide area network is a network that covers a large geographical area such as country or the world.

WAN combines many types of media such as telephone lines, cables and radio waves. A WAN can be one large network or can consist of two or more LANs connected together.

The Internet is the worlds largest WAN.

1.3.1 DIFFERENCES BETWEEN LAN & WAN

WAN Different LANA wide area network is a network that covers a large geographical area such as city, country or the world.

Geographical Area

A local area network is a network that connects computers and devices in a limited geographical area such as a home, school computer lab and office building

In case of WAN the cost of data transmission is very high because the transmission mediums used are hired either telephone lines or satellite links

Cost Cost of data transmission in LAN is less because the transmission medium is owned by a single organization

The speed of data transmission is lower than LAN

Speed The speed of data transmission is much higher in LAN than in WAN

1.3.1 DIFFERENCES BETWEEN LAN & WAN

WAN Different LANGeographical

Area

Cost

Speed

1.4 TYPES OF NETWORK ARCHITECTURE

A client is a computer that request services from a server computer

A server is a computer that provides services to clients and control access to hardware, software and other resources

1.4 TYPES OF NETWORK ARCHITECTURE

Client/Server

On a client/server network, one computer act as a server that provides services and the other computers (client) on the network request services from the server.

A server is a computer that controls access to the hardware, software and other resources on the network and provides a centralized storage area for program. There are many type of server such as mail server, web server, file server and ftp server.

A client is a computer that requests services from a server computer.

1.4 TYPES OF NETWORK ARCHITECTURE

Peer-to-peer

Peer-to-peer is a simple, inexpensive network that typically connects fewer than 10 computers. All computers in the network have equal capabilities to use the resources (hardware, software, data and files) available on the network. With peer-to-peer networks, there is no central server.

1.5 TYPES OF NETWORK TOPOLOGIESNetwork topology is the physical arrangement of computers in a network. Common network topologies include the bus, star and ring.

i) Ring TopologyOn a ring network, a cable forms a closed loop(ring) with all computers and devices arranged along the ring. Data transmitted on the network travels from device to device around the entire ring, in one direction. When a computer or device send data, the data travels to each computer on the ring until it reaches its destination.

If computer or device on a ring network fails, all devices before the failed device are unaffected but those after the failed device cannot function. 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 used in WANs.

Advantages A physical ring topology has minimal cable requirements No wiring center or closet needed The message can be automatically acknowledge No collision exist between nodes

Disadvantages If any node goes down, the entire ring goes down Troubleshooting is difficult because communication is only one way There will be a limit on the distance between nodes

1.5 TYPES OF NETWORK TOPOLOGIES

ii) Bus TopologyA bus network consists of single central cable, to which all computers and other devices connect. The bus is physical cable that connects the computers and others devices.

The bus in a bus network transmit data, instructions, and information and information in both directions. When sending device transmits data, the address of the receiving device is included with the transmission with the transmission so 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 point on the bus without disturbing the rest of the computers. The transmission simply by passes the failed device.

Advantages Easy to implement and extend Cost effective as only a single cable is used Cable faults are easily identified

Disadvantages Limited cable length and number of stations If there is a problem with the cable, the entire network goes down Maintenance costs may be higher in the long run Performance degrades as additional computers are added or on heavy traffic. Proper termination is required (loop must be in closed path)

1.5 TYPES OF NETWORK TOPOLOGIES

iii) Star Topology On a star network, all of the computers and devices(node) on the

network connect to central device, thus forming a star. The central device that provides a common connection point for nodes on the network is called the hub.

Similar to bus network, star networks are fairly easy to install and maintain. Nodes can be added to and removed from the network. On star network, if one node fails, one that node effected. The other nodes continue to operate normally. If the hub fails, however, the entire network inoperable until the hub is repaired. Most star networks, therefore, keep backup hubs available in case primary hub fails. A star network generally requires more cable.

Advantages Easy to install and wire No disruptions to the network then connecting or removing devices. Easy to detect faults and to remove parts More suited for larger networks Easy to expand network Easy to troubleshoot because problem usually isolates itself

Disadvantages Failure of the central hub causes the whole network failure It is slightly more expensive than using bus topology Requires more cable

1.6 DIFFERENCES BETWEEN BUS, RING & STAR TOPOLOGYTopology Bus Ring Star

Configuration

Central device Not available Not available Hub or switchData transmitted

Both direction One direction Both direction

Installation and maintenance

Easy Difficult Easy

If one node fails Does not effect the rest of

nodes

The entire network stop working

Does not effect the rest of nodes

1.7 TCP/IP as a protocol to facilitate communication over computer network

A protocol is a set of rules for the exchange of data between a terminal and computer or between two computers. Think of protocol as a sort of precommunication agreement about the form in which a message or data is to be sent and receipt is to be acknowledge.

TCP/IP is short for Transmission Control Protocol/Internet Protocol. TCP/P is a network standard, specifically a protocol, that defines how messages are routed from one end of a network to the other, ensures the data arrives correctly.

1.8 NETWORK COMMUNICATIONS TECHNOLOGY

INTERNETAn internet is a public network. It is worldwide collection of networks that links millions of business, government agencies, educational institutions and individuals.

INTRANETAn intranet is a private network within an organization that resembles the internet. Organizations use intranets to provide information to their employees.

Typically applications include electronic telephone directories, email addresses, employee information, internal job opening, and much more. Employees find surfing their organizational intranets to be as easy and as intuitive as surfing the Internet.

Like the public internet, intranet use browsers, web sites, and web pages. Intranet typically provides e-mail, mailing lists, newsgroup, and FTP services accessible only to those within the organization.

EXTRANETAn extranet is a private network that connects more than one organizations.

Many organizations use the Internet technologies to allow suppliers, customers and business partner limited access to their network.

The purpose is to increase efficiency and reduce costs.

For examples, Generals Motors has thousands of suppliers for parts that go into making an automobile. By having access to the production schedules, suppliers can schedule and deliver parts as they are needed at the General Motors assembly plants. In this way, General Motors can be assured of having adequate parts without maintaining large inventories.

DIFFERENCES INTERNET, INTRANET & EXTRANET

DIFFERENCES Internet Intranet ExtranetUsed for Public Private Private

Types of users Provide information for

public

Provide information for organization employees

Provide information to suppliers, customers and business partner

Usages Access all kinds of information

Telephone directories, Internal job openings, employee information

Access data, Check status Place orders, send email

Security Loose High Use virtual private network (VPN) technology to communication over the internet more secure

2.0 HARDWARE REQUIREMENTS FOR NETWORKING

NETWORK INTERFACE CARD (NIC) is a communication device that enables a computer or device to access a wired network (via cable).

COMMUNICATION DEVICES

A WIRELESS NETWORK INTERFACE CARD is a communication device that enables a computer or device to access a wireless network (via radiowave).

A MODEM is a communication device that enables a computer to transmit data over telephone or cable line. Modem converts digital signals from your computer into analog signals to send over the phone lines and converts the phone’s analog signals into digital for the computer.

A HUB is a communication device that is used for connecting wired computers or devices on a Local Area Network (LAN). A hub provides a common connection point for nodes on a star network.

A WIRELESS ACCESS POINT is a communication device that is used for connecting wireless computers or devices on a Local Area Network (LAN)

A ROUTER is a communication device that connects multiple computers and transmits data to its correct destination on the network. A router allows multiple computers to share a single high-speed internet connection.

Transmission media

TRANSMISSION MEDIA

PHYSICAL TRANSMISSION MEDIA

Send communication signal through tangible material such as wire and glass using electrical signal and pulses of light.1. Twisted pair cable2. Coaxial cable3. Fiber optic

WIRELESS TRANSMISSION MEDIA

Send communication signal through air or space using radiowave, microwave and infrared.1. Infrared2. Radiowave3. Satellite

2.3 TYPES OF CABLES

(a) Twisted pair cable

Description:Twisted pair cable consists of two strands of insulated copper wire, twisted around each other. Multiple twisted pairs can be combined into a single cable. This twisted-pair configuration somewhat reduces interference from electrical field.

How signal pass through:Transmit data by means electrical signal

(b) Coaxial CableDescription:

Coaxial cable consists of a single copper wire surrounded by at least three layer an insulating material, braided wires, plastic coating.

How signal pass through:Transmit data by means electrical signal

(b) Fiber OpticDescription:

Fiber consists of dozens or hundreds of thin strands of glass that use light to transmit signal. Each strand, call optical fiber, is as thin as human hair.

How signal pass through:Transmit data as pulses of light through tiny tubes of glass

2.4 WIRELESS TRANSMISSION MEDIA

(a) Infrared

Type of wireless transmission medium that sends signals using infrared light waves. To communicate each other, Infrared devices often must be within about 5 meters (15 feet)

(b) Radio wave

IEEE 802.15.1Bluetooth technology uses short-range radio waves to transmit data between two Bluetooth devices. The data transfers between devices at rate of 1 Mbps. To communicate each other, Bluetooth devices often must be within about 10 meters (33 feet).

IEEE 802.11 b/ IEEE 802.11 gWiFi (Wireless Fidelity): The data transfers between devices at a rate of 11 – 54 Mbps. To communicate each, WiFi devices often must be within about 30 meters (100 feet)

(c) SatelliteA satellite is a space station that receives microwaves signals from an earth-based station, amplifies (strengthens) the signals, and broadcasts the signal back over a wide area to any number of earth-based stations.

3.0 SOFTWARE REQUIREMENTS

3.1 DEFINITION OF NETWORKING OPERATING SYSTEM

Networking Operating System is an operating that is designed to support a network. Network operating system organizes and coordinate how multiples users access and resources on a network.

Resources include hardware, software, data and information. For example, NOS allows multiple uses to share a printer, internet access, files and programs.

Examples of Network Operating Systemsi) Netware vi) Linux (Red Hat, SUSE, KDE, Ubuntu)ii) Window Server 2000iii) UNIXiv) Windows NTv) Solaris

3.2 CLIENT SOFTWARE1. Web browser • A web browser is application software that allows users to

access and view web pages.• Web browsers have several main functions.

a. Retrieve and view internet-based information. They enables us to retrieve and view information from World Wide Web.

b.Interact with servers. They allow us to interact with server-based systems to submit information to this system.

c.View electronic documents. They are the foundation tool for viewing electronic documents.

d.Download and upload information. They let us download digital information, then view and/or hear the downloaded video, images, music, and so on. They let us upload information, as well.

e.E-mail. They allow us to send and receive e-mail.• Examples: Internet Explorer 7, Mozilla Firefox, Netscape

Communicator 7, Opera 6.0, Camino 1.0, Safari 1.2, GoSurf

2. Network utilities• Ping : to provide a check that a particular IP address is available

and reachable

3. Network file manager• My network places replaces the Network Neighborhood

feature that you used in both Window 98 and Windows NT 4.0• Function: to access files and folders on other computer in the

network

4. Email client• There are several function of e-mail client

a. To create e-mail messagesb. To send e-mail messagesc. To receive e-mail messagesd. To forward e-mail messagese. To store e-mail messagesf. To print e-mail messagesg. To delete e-mail messages

• Examples : Outlook Express, Mozilla Thunderbird