WEEK 6 (NETWORK TOPOLOGY)

NIC

     A network interface controller (also known as a network interface card, network adapter, LAN adapter and by similar terms) is a computer hardware component that connects a computer to a computer network.

Whereas network interface controllers were commonly implemented on expansion cards that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

     The network controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Wi-Fi, or Token Ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP. 

Network TOPOLOGY is divide by 3 ::

(1) Network topology

      - is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.

(2) Physical topology

     - Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network.

(3) Logical topology

- is the mapping of the flow of data between the nodes.

There are several basic types of topology in networks:

(1) BUS TOPOLOGY

A linear bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable.Ethernet and LocalTalk networks use a linear bus topology.The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more. If the workstation address matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.

Advantages of a Linear Bus Topology

• Easy to connect a computer or peripheral to a linear bus.
• Requires less cable length than a star topology.

Disadvantages

• Entire network shuts down if there is a break in the main cable.
• A faulty cable or workstation will take the entire LAN down
• terminators are required at both ends of the backbone cable.
• Difficult to identify the problem if the entire network shuts down.
• Not meant to be used as a stand-alone solution in a large building.

(2) STAR TOPOLOGY

A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator. Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow.This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.The protocols used with star configurations are usually Ethernet or LocalTalk.

Advantages

• Easy to install, and wire.
• Easy to add new workstations
• No disruptions to the network when connecting or removing devices.
• Any non-centralised failure will have very little effect on the network
• Easy to detect faults and to remove parts.
• Centralized control Centralized network/hub monitoring

Disadvantages

• Requires more cable length than a linear topology.
• If the hub or concentrator fails, nodes attached are disabled.
• More expensive than linear bus topologies because of the cost of the concentrators.

(3) STAR-WIRED

A star-wired topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring. The Token Ring protocol uses a star-wired topology.

(4) TREE TOPOLOGY

A tree topology combines characteristics of linear bus and star topologies.It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantage

• Point-to-point wiring for individual segments.

Disadvantages

• Overall length of each segment is limited by the type of cabling used.
• if the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies.

(5) ETHERNET

      Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless

ethernet cables

(6) LOCALTALK

     

    LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s.CSMA/CA was implemented as a random multiple access method.

LocalTalk cable adapter

connect directly to the Ethernet and LocalTalk

WEEK 5

INTRODUCTION TO NETWORKING

      A network is a collection of connected intelligent computing devices. The connection is not necessarily a fancy one. A connection between two computers by direct cabling is qualified to be a network. By this definition, a workstation which is loaded with a computer, a scanner, and a printer, is not treated as a network.

 








COMPUTER NETWORKING

      A computer network is simply two or more computers connected together so

they can exchange information.  A small network can be as simple as two

computers linked together by a single cable.

 

TYPE OF NETWORK

 








A network is a medium that connects computers around the world. With the network, information or data can be sent quickly without the limitations of distance and time.

     
 Computer networks are divided into five types:

1)      Local Area Network (LAN) is a small-scale private network inside the building.LANs are often used for connecting personal computers and workstations in a corporate office or factories to use shared resources (eg printers) and exchange information.

2)      Metropolitan Area Network (MAN) basically a LAN version of the larger size and usually use the same technology to the LAN. MAN could include corporate offices are located adjacent or also a town and can be used for private purposes (private) or public. MAN is able to support data and voice, even may be associated with cable television network.

3)      Wide Area Network (WAN) its scope covers a wide geographical area, often covering a country or even continent. WAN consists of a collection of machines that aim to run the programs (applications) user.

4)      Internet, Actually there are many in this world networks, often using hardware and software that is different. People who connect to the network often wish to communicate with others who connect to other networks. These desires need relationships between networks that are often not kampatibel and different. Usually to do this required a machine called a gateway in order to have sex and perform the necessary translation, both hardware and software. A collection of interconnected networks is called the Internet.

5)      Wireless Networking is a solution to the communication can not be done by using a cable network. For example, people who want to get information or to communicate despite being on top of a car or plane, it is absolutely necessary because the cable network without a cable connection is not possible to be made in the car or plane.Currently, wireless networks have rapidly adopted the use of satellite services and can provide faster access speeds than the network cables.

NETWORK COMPONENT

      In order for a computer to operate on a network, there are a range of different components that are required.  As part of the OCR syllabus, you need to be able to describe various devices and explain their role within a network

ROUTER

      A Router is a device that transfers data from one network to another in an intelligent way. It has the task of forwarding data packets to their destination by the most efficient route.

      In order to do this, the router has a micro computer inside it.  This holds a table in memory that contains a list of all the networks it is connected to, along with the latest information on how busy each path in the network is, at that moment. This is called the 'routing table'.

Function of router is:

1)      Reads the data packet's destination address

2)      Looks up all the paths it has available to get to that address.          

3)      Checks on how busy each path is at the moment     

4)      Sends the packet along the least congested (fastest) path

                                                                                                                                  BRIDGE                                                                                                                               

      A Bridge does just what you would expect it to do - it joins two networks together so as far as data packets are concerned it looks like one large network.

PROTOCOL

      A 'protocol' is a rather technical word. But it simply means an agreed method of doing something.

      A 'NETWORK PROTOCOL' is the agreed method of communication to be used within the network.

      Elements of a network protocol:

Ø  The list below indicates some the things that  need to  be considered:-

1)      Speed of the network - for example 10Mbit /s

2)      Error checks of the data packets when they arrive- how is it done

3)      Error correction of the data packets - method to be used

4)      Data packets received correctly - what method/signal will be used to tell the other machine that the data has arrived correctly

5)      How does the receiving machine know that the sending machine has finished sending all of the data? - what is the code to indicate this

6)      Data compression - does the protocol allow this to take place and if so, what method does it use?

Ø  There are many protocols in use across various networks:

1)      TCP - the protocol that the internet uses

2)      Kermit - popular for use with modems

3)      X.25 - a packet switched protocol

      Anyone can invent a protocol. Indeed some large companies develop their own often hoping the rest of the world will use it as well.

      Most widely used network protocols have been agreed and developed by international standards organisations such as the ITU (International Telecommunication Union).

GATEWAY

      A gateway converts the data passing between dissimilar networks so that each side can communicate with each other.

      The gateway is a mixture of hardware components and software.

HUB

      The network 'Hub' allows computers to share data packets within a network.

      Each computer will be connected to a single 'port' on the hub. So if you purchase an '8 port hub', you will be able to connect up to eight computers together.

      You can also 'daisy chain' hubs to allow even more computers to join the network.

 

SWITCH

      A switch has a number of ports and it stores the addresses of all devices that are directly or indirectly connected to it on each port.

      As a data packet comes into the switch,  its destination address is examined and a direct connection is made between the two machines.

END NODES

      Within a vast computer network, the individual computers on the periphery of the network, those that do not also connect other networks, and those that often connect transiently to one or more clouds are called end nodes. Typically, within the cloud computing construct, the individual user / customer computer that connects into one well-managed cloud is called an end node. Since these computers are a part of the network yet unmanaged by the cloud's host, they present significant risks to the entire cloud. This is called the End Nodes problem. There are several means to remedy this problem but all require instilling trust in the end node computer.

BLUETOOTH

      Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area network (PANs) with high levels of security. It can connect several devices, overcoming problems of synchronization. The devices can switch roles, by agreement, and the slave can become the master. At any given time, data can be transferred between the master and one other device.

 

INFRA-RED

      This is a very familiar method of transferring data if you are at all aware of your remote control ! The television remote control makes use of an infra-red link. Personal organisers often make use of an infra-red link to synchronise calendars and 'to-do' lists.

WEEK 3 (DATA COMMUNICATION)

DATA COMMUNICATION ?

-Data Communications is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it. The actual generation of the information is not part of Data Communications nor is the resulting action of the information at the receiver. Data Communication is interested in the transfer of data, the method of transfer and the preservation of the data during the transfer process.
-Data communication is, vey simply, the collection and disrtibution of the electronic representation of information from and to remote facilities by means of electrical transmission systems such as telephone lines, satellites or coaxial cable. The information can appear in a variety of formats; data, text, voice, still pictures, graphics and vedio. Prior to transmission, the raw information must be digitised.


WHAT IS "MODEM" ???

-Modems are often used to enable computers to communicate with each other across telephone lines. A modem converts the digital signals of the sending computer to analog signals that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer.

To convert a digital signal to an analog one, the modem generates a carrier wave and modulates it according to the digital signal. The process of receiving the analog signal and converting it back to a digital signal is called demodulation. The word "modem" is a contraction of its two basic functions: modulation and demodulation.

COAXIAL CABLE ??

-Coaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor.

The outer shield protects the inner conductor from outside electrical signals. The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than Twisted Pair cable.

OPTICAL FIBRE??

-Optical Fibre consists of thin glass fibres that can carry information at frequencies in the visible light spectrum and beyond. The typical optical fibre consists of a very narrow strand of glass called the Core. Around the Core is a concentric layer of glass called the Cladding. A typical Core diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns. Coating the cladding is a protective coating consisting of plastic, it is called the Jacket.

AMPLITUDE,PERIOD AND FREQUENCY..

 
Analog signal on the other hands, is like the human voice. It is formed by continuously varying voltage levels that create a wave that can be grasped by an analogue transmitter like microphone. This analogue signal features involves 2 parameters, which are frequency and amplitude as shown in figure.
Amplitude (A): how high the peaks are or how low the troughs are, in meters.

The displacement is how far the wave vibrates / oscillates about its equilibrium (center) position.

Amplitude is correlated with the total energy of the system in periodic motion. Larger amplitude = greater energy.

Period (T): the time it takes for one cycle, in seconds.

Frequency (f): the rate, or how many cycles per second, in Hertz (cycles per second).

DATA TRANSMISSION ???
 Digital transmission is the language of computer. The physical connection determines how many bits (1's or 0's) can be transmitted at a single instance of time. If only 1 bit of information can be transmitted over the data transmission medium at a time then it is considered a Serial Communication.

Digital signal need to be changed into analogue signal to be transmitted through PSTN lines that act as the media transmission.the process of changing analogue to digital signal is called modulation and process of changing its back to the analogue form is called demodulation. MoDem is the hardware that used in computer to do this process.


WHAT IS DATA FLOW ???

-Data flow is the flow of data between 2 points. The direction of the data flow can be described as:

1) SIMPLEX

-Simplex: data flows in only one direction on the data communication line (medium). The role of the transmitter and the receiver are fixed. Examples are Radio and Television broadcasts. They go from the TV station to your home television.

 

2) HALF DUPLEX

-data flows in both directions but only one direction at a time on the data communication line. One station transmitts information to anoyher station without any interruption. Examples, conversation on walkie-talkies is a half-duplex data flow. Each person takes turns talking. If both talk at once so that will not occur!

 

3) FULL DUPLEX

-Data flows in both directions simultaneously. Its consists of two simplex channels are channel is used to forward while the other as the reversal channel, linking at the same point. Modems are configured to flow data in both directions.

 

WEEK 2 (WEB BROWSER)

WHAT IS WEB BROWSER ???

A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier (URI) and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users easily to navigate their browsers to related resources. A web browser can also be defined as an application software or program designed to enable users to access, retrieve and view documents and other resources on the Internet.

Although browsers are primarily intended to access the World Wide Web, they can also be used to access information provided by web servers in private networks or files in file systems. The major web browsers are Firefox, Google Chrome, Internet Explorer, Opera, and Safari.

Examples of web browser::

• Microsoft Internet Explorer
• Mozilla Firefox,
• Apple Safari
• Netscape
• Opera

METASEARCH ENGINE ??

-A metasearch engine is a search tool that sends user requests to several other search engines and/or databases and aggregates the results into a single list or displays them according to their source. Metasearch engines operate on the premise that the Web is too large for any one search engine to index it all and that more comprehensive search results can be obtained by combining the results from several search engines. This also may save the user from having to use multiple search engines separately.

Examples of METASEARCH ENGINE:

BOOKMARK (WORLD WIDE WEB)???

-In the context of the World Wide Web, a bookmark is a locally stored Uniform Resource Identifier (URI). All modern web browsers include bookmark features. Bookmarks are called favorites or Internet shortcuts in Internet Explorer. Bookmarks are normally accessed through a menu in the user's web browser, and folders are commonly used for organization. In addition to bookmarking methods within most browsers, many external applications offer bookmark management. Bookmarks have been incorporated in browsers since the Mosaic browser in 1993. Bookmark lists were called Hotlists in Mosaic and in previous versions of Opera; this term has faded from common use. Other early web browsers such as ViolaWWW and Cello also had bookmarking features.

With the advent of social bookmarking, shared bookmarks have become a means for users sharing similar interests to pool web resources, or to store their bookmarks in such a way that they are not tied to one specific computer or browser. Web-based bookmarking services let users save bookmarks on a remote web server, accessible from anywhere.

CLEAR HISTORY ??

-Clear History is free and powerfull windows desktop application to clean search history from your computer. It is full featured program that greatly surpasses most commercial programs out there. What does it clear :

• Clear search history (browser history)
• Clear typed URL-s (website address)
• Clear location bar history ( option to exclude URL-s from clearing)
• Clear cache (temporary internet files)
• Clear cookies (with option to exclude some cookies from deleting)
• Clear autocomplete forms and passwords
• Clear index.dat files
• Delete recent documents (in Windows)
• Delete run history
• Delete find computers history
• Delete Windows temporary files
• Delete Recycle Bin without recovery (shred it after deleting)
• Clear clipboard (memory space reserved for copy/paste operations)
• Clear Windows Open/Save dialog history
• Clear tracks from Ms Office, Word, Excel, Access, Power Point and Front Page
• Clear tracks from WinZip, WinRar, Windows Media Player, Wordpad, Media Player Classic

WHAT IS CLEAR CACHE(VIDEO)???

-Cache files are nothing but regular files from web pages you visited, pictures, videos etc. Those files are used by browser instead of downloading again so your pages load faster. But, cache files are an evidence of where you have been and what you were doing on internet. So if you don't want your internet habits to be discovered you should clear cache on regular basis. To clear cache in your web browser is very straightforward - follow the instructions bellow.

To clear cache from your computer do the following:

     In Firefox:

• Go to the Tools menu
• Select Clear Private Data
• Make sure Cache is checked. Uncheck others as you wish.
• Click on Clear Private Data Now and your cache is cleared.

CLEAR URL HISTORY ???

-If you don't clear URL history files, your web browser automatically keeps a detailed record of all web sites you've visited usually for more than forty days. The history feature enables you to have a more exact internet surfing experience. However if you want to eliminate only specific private searches from your URL history because there are other users of your PC who would like their URLs logged, you can selectively clear URL history files.If you don't clear URL history files, your web browser automatically keeps a detailed record of all web sites you've visited usually for more than forty days. The history feature enables you to have a more exact internet surfing experience. However if you want to eliminate only specific private searches from your URL history because there are other users of your PC who would like their URLs logged, you can selectively clear URL history files.

MULTITASKING ??

-The ability to execute more than one task at the same time, a task being a program.

In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.

PLUG-IN ???

In computing, a plug-in (or plugin) is a set of software components that adds specific abilities to a larger software application. If supported, plug-ins enable customizing the functionality of an application. For example, plug-ins are commonly used in web browsers to play video, scan for viruses, and display new file types. Well-known plug-ins examples include Adobe Flash Player, QuickTime, and Microsoft Silverlight.

Among popular plug-ins to download are Adobe's Acrobat, a document presentation and navigation program that lets you view documents just as they look in the print medium, RealNetworks' streaming video player, and Macromedia's Shockwave for DIrector, an interactive animation and sound player. There are now hundreds of possible plug-ins. Most users wait until they need a particular plug-in before they download it.