CHAPTER 3 COMPUTER NETWORKS & COMMUNICATIONS 1.1 BASIC CONCEPTS OF COMPUTER NETWORKSDefinition of Computer NetworksA computer network is a collection of computers anddevices connected together via communication devices andtransmission media. For example it may connectcomputers, printers and scanners.Definition of CommunicationCommunication describes a process in which two or morecomputer or devices transfer data, instructions andinformation.
1.2 THE IMPORTANCE/ADVANTAGES OF COMPUTER NETWORKSi. 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)
Network communications technologyIntranet Extranet Internet
1.3 TYPES OF COMPUTER NETWORKS A local area network is a network that connects computersLocal Area Network and devices in a limited geographical area such as a home, (LAN) school computer laboratory, office building. A metropolitan area network (MAN) is a high speed networkMetropolitan Area that connects local area networks in a metropolitan area Network (MAN) 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. A wide area network is a network that covers a largeWide Area Network geographical area such as country or the world. (WAN) 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 Geographical A local area network is a networknetwork that covers a large Area that connects computers andgeographical area such as devices in a limited geographicalcity, country or the world. area such as a home, school computer lab and office buildingIn case of WAN the cost of Cost Cost of data transmission in LANdata transmission is very is less because the transmissionhigh because the medium is owned by a singletransmission mediums organizationused are hired eithertelephone lines or satellitelinksThe speed of data Speed The speed of data transmission istransmission is lower than much higher in LAN than in WANLAN
1.3.1 DIFFERENCES BETWEEN LAN & WANWAN Different LAN Geographical Area Cost Speed
1.4 TYPES OF NETWORK ARCHITECTUREA server is acomputer thatprovidesservices toclients andcontrol accessto hardware,software andotherresources A client is a computer that request services from a server computer
1.4 TYPES OF NETWORK ARCHITECTUREClient/ServerOn a client/server network, one computer act as a serverthat provides services and the other computers (client) onthe 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 providesa centralized storage area for program. There are many typeof server such as mail server, web server, file server and ftpserver.A client is a computer that requests services from a servercomputer.
1.4 TYPES OF NETWORK ARCHITECTUREPeer-to-peerPeer-to-peer is a simple, inexpensive network that typicallyconnects fewer than 10 computers. All computers in the networkhave equal capabilities to use the resources (hardware, software,data and files) available on the network. With peer-to-peernetworks, there is no central server.
1.5 TYPES OF NETWORK TOPOLOGIESNetwork topology is the physical arrangement of computers in anetwork. Common network topologies include the bus, star and ring.i) Ring Topology On 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 nodesDisadvantages 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 TOPOLOGIESii) Bus Topology A 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 identifiedDisadvantages 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 TOPOLOGIESiii) 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 itselfDisadvantages 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 TOPOLOGY Topology Bus Ring StarConfigurationCentral device Not available Not available Hub or switchData Both direction One direction Both directiontransmittedInstallation and Easy Difficult EasymaintenanceIf one node fails Does not effect The entire Does not effect the rest of network stop the rest of nodes nodes working
1.7 TCP/IP as a protocol to facilitate communication over computer networkA protocol is a set of rules for the exchange of data between a terminaland computer or between two computers. Think of protocol as a sort ofprecommunication agreement about the form in which a message ordata 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 howmessages are routed from one end of a network to the other, ensuresthe data arrives correctly.
1.8 NETWORK COMMUNICATIONS TECHNOLOGYINTERNETAn internet is a public network. It is worldwide collection of networksthat links millions of business, government agencies, educationalinstitutions and individuals.INTRANETAn intranet is a private network within an organization that resemblesthe internet. Organizations use intranets to provide information to theiremployees.Typically applications include electronic telephone directories, emailaddresses, employee information, internal job opening, and much more.Employees find surfing their organizational intranets to be as easy andas intuitive as surfing the Internet.
Like the public internet, intranet use browsers, web sites, and webpages. Intranet typically provides e-mail, mailing lists, newsgroup, andFTP services accessible only to those within the organization.EXTRANETAn extranet is a private network that connects more than oneorganizations.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 gointo making an automobile. By having access to the production schedules,suppliers can schedule and deliver parts as they are needed at the GeneralMotors assembly plants. In this way, General Motors can be assured ofhaving adequate parts without maintaining large inventories.
DIFFERENCES INTERNET, INTRANET & EXTRANET DIFFERENCES Internet Intranet ExtranetUsed for Public Private PrivateTypes of users Provide Provide information Provide information information for for organization to suppliers, public employees customers and business partnerUsages Access all kinds of Telephone Access data, Check information directories, Internal status Place orders, job openings, send email employee informationSecurity Loose High Use virtual private network (VPN) technology to communication over the internet more secure
2.0 HARDWARE REQUIREMENTS FOR NETWORKING COMMUNICATION DEVICESNETWORK INTERFACE CARD (NIC) is a communication device thatenables a computer or device to access a wired network (via cable).A WIRELESS NETWORK INTERFACE CARD is a communication devicethat enables a computer or device to access a wireless network (viaradiowave).A MODEM is a communication device that enables a computer totransmit data over telephone or cable line. Modem converts digitalsignals from your computer into analog signals to send over the phonelines and converts the phone’s analog signals into digital for thecomputer.
A HUB is a communication device that is used for connecting wiredcomputers or devices on a Local Area Network (LAN). A hub provides acommon connection point for nodes on a star network.A WIRELESS ACCESS POINT is a communication device that is used forconnecting wireless computers or devices on a Local Area Network(LAN)A ROUTER is a communication device that connects multiplecomputers and transmits data to its correct destination on thenetwork. A router allows multiple computers to share a single high-speed internet connection.
TRANSMISSION MEDIA Transmission media PHYSICAL TRANSMISSION WIRELESS TRANSMISSION MEDIA MEDIASend communication signal Send communication signalthrough tangible material such through air or space usingas wire and glass using radiowave, microwave andelectrical signal and pulses of infrared.light. 1. Infrared1. Twisted pair cable 2. Radiowave2. Coaxial cable 3. Satellite3. Fiber optic
2.3 TYPES OF CABLES (a) Twisted pair cableDescription: 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) InfraredType of wireless transmission medium that sends signals using infraredlight waves. To communicate each other, Infrared devices often mustbe within about 5 meters (15 feet) (b) Radio waveIEEE 802.15.1Bluetooth technology uses short-range radio waves to transmit databetween two Bluetooth devices. The data transfers between devicesat rate of 1 Mbps. To communicate each other, Bluetooth devices oftenmust be within about 10 meters (33 feet).
IEEE 802.11 b/ IEEE 802.11 gWiFi (Wireless Fidelity): The data transfers between devices at a rateof 11 – 54 Mbps. To communicate each, WiFi devices often must bewithin about 30 meters (100 feet)(c) SatelliteA satellite is a space station that receives microwaves signals from anearth-based station, amplifies (strengthens) the signals, andbroadcasts the signal back over a wide area to any number of earth-based stations.
3.0 SOFTWARE REQUIREMENTS 3.1 DEFINITION OF NETWORKING OPERATING SYSTEMNetworking Operating System is an operating that is designed tosupport a network. Network operating system organizes andcoordinate how multiples users access and resources on a network.Resources include hardware, software, data and information. Forexample, 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 reachable3. 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 messages b. To send e-mail messages c. To receive e-mail messages d. To forward e-mail messages e. To store e-mail messages f. To print e-mail messages g. To delete e-mail messages • Examples : Outlook Express, Mozilla Thunderbird
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