MODULE NAME: FOUNDAMENTALS OF INFORMATION …



Syllabus Focus: Unit 1 Module 2 Content 7Specific Objective 7: describe the purpose and functions of network components;Content: Purpose, functions and types of networks including local area network (LAN), wide area network (WAN), metropolitan area network (MAN); virtual private network (VPN); Internet; Intranet; Extranet; configuration; topologies; transmission media: (wired versus wireless): fibre-optic, Unshielded Twisted Pair (UTP); hotspots,protocols; definitions and examples; network security; firewalls. TOPIC: Computer NetworksCommunication ChannelsData communication forms an integral part of the computer world. Using this technology, computers and other devices (such as printers and storage devices) can communicate via communication channels. A communication channel is the path that facilitates the communication and is composed of one or more transmission media. These media can be either physical or wireless.Physical Communication ChannelsPhysical communication channels, which are specialized cables (e.g. twisted-pair, coaxial or fiber-optic cables) are used to connect computers and their peripherals to form computer WORKSA computer network is made up of a number of connected computers each with their own processor, for example a number of connected PCs. Networks are popular because they provide a number of users with access to resources (e.g. data files, printers, software). Therefore, a network allows computing resources to be used more efficiently between a group of users. In some computer networks, a device is connected directly to another device by a dedicated communication channel, giving those devices sole use of that channel. These are called point-to-point transmission computer networks. In a multi-point transmission computer network, one channel is used to connect three or more devices. In general, a multi-point configuration uses a communication channel more efficiently than a point-to-point configuration. It reduces the amount of inter-cabling needed thus lowering costs. A point-to-point configuration, on the other hand, is very useful in systems that require high-speed response.InternetA global network connecting millions of computers. More than 100 countries are linked into exchanges of data, news and opinions. It is possible to gain access through a commercial Internet Service Provider (ISP). The Internet is not synonymous with World Wide Web. The Internet uses a capability known as the World Wide Web. World Wide Web is a system of universally accepted standards of storing, retrieving, formatting, and displaying information in a networked environment. Information is stored and displayed as electronic “pages” that contain text, graphics, animations, sound and video, called web pages. These web pages can be linked electronically to other web pages, regardless of where they are located and viewed by any computer. The web can serve as the foundation for new kinds of information systems, product and services. All of the web pages maintained by an organization or individual are called a web site.Intranet A network based on TCP/IP protocols (an internet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access. Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols. ExtranetA buzzword that refers to an intranet that is partially accessible to authorized outsiders. Whereas an intranet resides behind a firewall and is accessible only to people who are members of the same company or organization, an extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view. Extranets are becoming a very popular means for business partners to exchange information. NETWORK CLASSIFICATIONSLocal Area Network (LANs)A local area network (LAN) is a network of computers located in a single building, a single site, an office suite or a group of buildings. It connects devices that are confined to a relatively small geographical area. The parts of the network are linked by computer cable rather than via telecommunications lines.LAN CharacteristicsFlexibility – Many different hardware devices e.g. plotters, printers and computers can be attached to a LAN.Speed – high speed data transferReliabilityHardware and software sharingTransparent interface – network access for users should not be complicated.Adaptability – can accommodate a variety of hardware and can be reconfigured easily.Access to other LANs and WANsSecurityCentralized ManagementPrivate ownership of the LANWide-Area Network (WAN)A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet. At each end of the leased line, a router connects to the LAN on one side and a hub within the WAN on the other. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET/SDH, MPLS, ATM and Frame relay are often used by service providers to deliver the links that are used in WANs.Metropolitan-Area Networks (MANs)A data network designed for a campus, town or city. They typically use wireless infrastructure or optical fiber connections to link their sites. For instance a university or college may have a MAN that joins together many of their local area networks (LANs) situated around site of a fraction of a square kilometer. Then from their MAN they could have several wide area network (WAN) links to other universities or the Internet.Benefits of NetworksSpeed - Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files (referred to as sneaker-net) is very time-consuming. Cost - Networkable versions of many popular software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations. Security - Files and programs on a network can be designated as "copy inhibit," so that you do not have to worry about illegal copying of programs. Also, passwords can be established for specific directories to restrict access to authorized users. Centralized Software Management - One of the greatest benefits of installing a network is the fact that all of the software can be loaded on one computer (the file server). This eliminates that need to spend time and energy installing updates and tracking files on independent computers throughout the building. Resource Sharing - Sharing resources is another area in which a network exceeds stand-alone computers. Most schools cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users. Electronic Mail - The presence of a network provides the hardware necessary to install an e-mail system. E-mail aids in personal and professional communication, and it facilitates the dissemination of general information. Electronic mail on a LAN can enable persons to communicate. If the LAN is connected to the Internet, persons can communicate with others throughout the world. Flexible Access - Networks allow users to access their files from computers throughout the network. Persons can also work cooperatively through the network. Workgroup Computing - Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently. For example, educators located at various schools within a county could simultaneously contribute their ideas about new curriculum standards to the same document and spreadsheets. Sharing SoftwareSharing DataSharing System resourcesSecurity and backup – Using security resources of a network, software can be safeguarded by installing passwords, trustee rights and file attributes.Easy maintenance and upgradesDisadvantages of Installing a NetworkExpensive to Install - Although a network will generally save money over time, the initial costs of installation can be prohibitive. Cables, network cards, and software are expensive, and the installation may require the services of a technician. Requires Administrative Time - Proper maintenance of a network requires considerable time and expertise. File Server May Fail - Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire network may lose access to necessary programs and files. Cables May Break - The topology refers to the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network. There is an increased risk of data corruption. Since many users will be using the system, there is a greater chance of data being corrupted or tampered with.There is a greater risk from viruses, because they are usually spread between the work Topology is the configuration or physical arrangement of the devices or nodes. i.e. The layout of the computers and devices on a network. The 3 main topologies are ring, star and bus.BusA bus network is a network architecture in which there is a single central cable to which all devices are attached. The central cable is called a bus. The bus transmits data in both directions. Only one device can transmit at a time. 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. It is easy to add/remove devices from a bus network. It is also an inexpensive topology. Failure of one device does not affect another device. The network will fail if the bus (central cable) fails.114300067945Advantages of a Bus Topology Easy to connect a computer or peripheral to a linear bus. Typically the cheapest topology to implement Failure of one station does not affect others Disadvantages of a Bus TopologyEntire network shuts down if there is a break in the main cable. Terminators are required at both ends of the backbone cable. Difficulty in identifying the problem if the entire network shuts down.Performance degrades as additional computers are added Ring1905000595630A ring network is a topology where each device is connected to two others, so as to create a ring or closed loop. Data transmitted on a ring network travels in one direction on the ring from device to device until it reaches its destination. If a device fails, devices before it are not affected, it is the devices after it that are affected.Advantages of Ring NetworkGrowth of the system has minimal impact on performance All stations have equal access Each node on the ring acts as a repeater (booster of the signal), allowing ring networks to span greater distances than other physical topologies. Because data travels in one-direction high speeds of transmission of data are possible. Disadvantages of Ring NetworkOften the most expensive topology Failure of one computer may impact others StarA star network topology, in its simplest form, consists of one central, or hub computer, which acts as a router to transmit messages. All devices are connected to the central computer (hub). All data passes through the hub. If a device fails, there is no effect on the network, only if the hub fails will the network be affected.125730085725Advantages of Star NetworkEasy to implement and extend, even in large networks Well suited for temporary networks (quick setup) The failure of a non-central node will not have major effects on the functionality of the network. Disadvantages of Star NetworkLimited cable length and number of stations Maintenance costs may be higher in the long run Failure of the central node (hub) can disable the entire networkCentral hub can be a bottleneck.Other topologies include mesh and extended star.Tutorial Questions1. Differentiate between the internet, intranet and extranet. 2. With the aid of diagrams differentiate between the bus, ring and star networks.3. Identify two advantages and two disadvantages of the bus, ring and star networks.4. Which network will fail if the central cable breaks?Networks in Brief- A network is two or more computers linked together with cables, microwave links or wireless radio connections.- Network topology describes its logical wiring shape: bus, ring, star, tree, mesh- A network message is called a packet, frame or datagram, and contains (at least) a source network address, a destination network address and data.?- A network's architecture or technology (e.g. Ethernet, Token Ring or ATM) describes how packets are handled and transported.- A protocol is an agreed set of rules that describe how communications should occur (e.g. TCP/IP, HTTP, FTP, POP)- Network sizes are local (LAN), metropolitan (MAN) and wide (WAN).? The Internet is an interconnection of WANs.? Peer-to-peer networks are simple, trusting networks with no server.- File servers run the Network Operating System and control the network's services.? Powerful application servers run applications, such as word processors, for users.? - In Client-Server networking, one program requests another program to provide a service or data. In Peer-to-peer, each computer has equal privileges and power.- Networks can save money by sharing expensive devices between users.? They allow quick and easy communication, collaboration and information exchange.- IP (Internet Protocol) addresses give each Internet user a unique address.? DHCP is a service that allocates IP addresses to network users.- Telnet lets users log on to and control a remote computer- Virtual Private Networks (VPN) give private network channels across the Internet.- Remote control software lets technicians and help desk operators view and control remote computers as if they were sitting at the keyboard.- Videoconferencing over networks saves organisations travel time and expense- An intranet is a local version of the Internet which not available beyond the LAN or WAN.- Networks can centralise file storage, backups, virus scanning, CD-ROM distribution, Internet caching, software distribution etc.- Servers are powerful, expandable and robust computers at the heart of a network.? Specialist servers (e.g. print servers, web servers, login servers) help ease the workload of a single server.- The Network Operating System is the software that controls network operations and services.? Workstations need client software to interact with the NOS.- The NIC (Network Interface Card) connects a workstation to the network.- A router is a security device between a network and the outside world.- A hub lets one network cable be divided amongst many workstations.? A switch is a hub that intelligently filters out irrelevant network traffic.- Every device that needs to communicate with other devices needs a network address, and is called a node.- Bandwidth is a measure of data-carrying capacity in bits per second.- The most common network cable is Category 5e or 6 (CAT5e or CAT6), a form of UTP (Unshielded Twisted Pair).? Coaxial cable is often used as network backbone cables.? Fibre Optic Cable has very high speed, very high bandwidth capacities.- A backbone is a high-speed, high capacity data channel, usually connecting different network segments.- Network security requires user authentication using individual user logins with passwords or biometric identification.- Servers must be physically protected against damage and unauthorised access.? They must be backed up regularly to protect against data loss, and organisations should have a data disaster recovery plan. - Encryption of data prevents anyone being able to use it, even if they can get access to it.- Firewalls protect computers against hacking attacks by blocking unauthorised incoming or outgoing Internet traffic.? Virus scanners protect against viruses.- In a bus topology, a single cable has nodes branching from it.- In a ring topology each node has a neighbour before and after it, and packets travel around the ring to each node.- In a star topology all nodes are connected directly to a central device such as a server and a switch.- A tree topology is made up of a bus connected to a star. When two dissimilar topologies combine, it's sometimes called hybrid.- In a mesh topology nodes have multiple connections to other nodes to provide multiple redundancy in case any connection fails.- Modems convert digital computer data to analogue (sound) and transmit it over telephone systems.? At the other end, another modem converts analogue back to digital data.- ADSL also uses telephone lines, but operates digitally at high speed.- Microwave connections are high-bandwidth line-of-sight data channels, most frequently used within cities.- Satellite connections offer high speed downloads, but need a normal modem connection to upload data.- ISDN are high-speed digital landlines, often leased as private channels between LANs.- Cable Internet provides a high-speed data channel to an Internet Service Provider (ISP).- Wireless networking uses radio transmissions to connect a node to the network.- NICs have a unique network address built into them to identify a node to the network.- Dynamic IP addresses only last the duration of an Internet connection.? Static IP addresses are more or less permanently assigned to a node on the Internet.- A URL (Uniform Resource Locator) is a human-friendly word-based version of a numeric IP address (e.g. ).- A DNS (Domain Name Server) looks up URLs in a distributed database and converts them into IP addresses that are actually used to route Internet traffic- An email address is made up of a username, "@" and a domain name, e.g. fred@- MAC (Media Access Control) addresses commonly identify nodes in a wireless network.- Ethernet is the most widely used LAN technology, and uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to manage network traffic flow.- Token Ring technology uses a special Token frame that circulates around the network.? A node must hold the Token to transmit across the network.- TCP/IP, Ethernet and Token Ring all use packet switching to send network messages.? Files and network messages are broken up into packets before being sent.?- TCP/IP is a pair of protocols universally used for Internet communications.? TCP breaks files into packets before they are sent and reassembles incoming packets into files.? IP manages the packets' journey to their destination.- The Internet is an interconnection of WANs, is based on TCP/IP communications, and forms a mesh topology.? It includes the World Wide Web, Usenet (newsgroups), FTP, ICQ chat, email and more. ................
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