WIRELESS TRANSMISSION MEDIA SUCH AS INFRARED, RADIO WAVE AND SATELLITE.

WIRELESS TRANSMISSION MEDIA SUCH AS INFRARED, RADIO WAVE AND SATELLITE..

Wireless Technology

In a wireless media however, signal transmission is unguided and the device communicates without using wires between nodes, usually by relying on radio frequencies instead.

INFRARED

• Infrared is a wireless transmission medium that sends signals using infrared light waves. Infrared is used in devices such as the mouse, wireless keyboard and printers. Some manufacturers provide a special port called the IrDA port that allows a wireless keyboard to communicate with a PC. Infrared signals have frequencies between 300 GHz to 400 THz.

RADIO WAVE

• Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. When an antenna transmits radio waves, they are propagated in all directions. This means that the sending and receiving antennas do not have to be aligned. Our AM and FM radio stations, cordless phones and televisions are examples of multicasting.

SATELLITE

• Satellite is an object which has been placed into orbit by human endeavor. A communication satellite is a space station that receives microwave signals from an earth-based station, amplifies (strengthen) the signals, and broadcasts the signals back over a wide area to any number of earth-based stations.

MEDIUM

Identify various types of cables such as Unshielded Twisted Pair (UTP), Shielded Twisted Pair (STP), coaxial and fiber optic cable

Shielded Twisted-Pair Cable

• Its Four pairs of colour-coded wires are each wrapped in metallic foil, and all four are then collectively wrapped in a layer of metallic braid or foil. Finally, this layer is wrapped with outer jacket.

Unshielded Twisted-Pair Cable

• Consist of two wires or conductor twisted together, each with it own plastic insulation. Cancel out the electromagnetic interference that can cause crosstalk, the noise generated by adjacent pairs.

Coaxial Cable

• The coaxial cable, often referred to as ‘coax’, consists of a single copper wire surrounded by at least three layers. They are an insulating material, a woven or braided metal and a plastic outer coating. This cable is often used as cable television (CATV) network wiring because it can be cabled over longer distances in comparison to the twisted-pair cable.

Fibre Optic Cable

• The fibre optic cable is a networking medium that uses light for data transmission. The intensity of light is increased and decreased to represent binary one and zero. The binary system is a way of counting using just the two numbers 0 and 1.

DEVICES NEEDED IN COMPUTER NETWORK COMMUNICATION..

MODEM

• A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines.
• Use to convert digital signal to analog signal and vise versa.

NIC ( NETWORK INTERFACE CARD)

• Network Interface Card (NIC) is also commonly referred to as a network adapter and is an expansion card that enables a computer to connect to a network using a given protocol.

WNIC ( WIRELESS NETWORK INTERFACE CARD)

• Wireless Network Interface Card (WNIC) is a network card that provides wireless data transmission. This card uses an antenna to communicate through microwaves.

WIRELESS ACCESS POINT

• A Wireless Access Point is a central communications device that allows computers and devices to transfer data wirelessly to a wired network using Wi-Fi, Bluetooth or related standards.

ROUTER

• A network device that forwards packets or data from one network to another according to the packet’s destination address.

SWITCH / HUB

• A hub or switch is a device that provides a central point for cables in a network. Switches allow user to send information, such as email, and access shared resources, including printers

INTERNET, INTRANET, EXTRANET

INTERNET..

- The Internet is a global system of interconnected computer networks use the standard
Internet Protocol Suite (TCP/IP) to serve billions of users worldwide

- It is a network of networks that consists of millions of private, public, academic,
business, and government networks, of local to global scope, that are linked by a
broad array of electronic and optical networking technologies

INTRANET..

- An intranet is a private computer network
- Use Internet Protocol technologies to securely share any part of an organization's
information within that organization
- Example of intranet application: telephone directories, job posting, event
calendars
- Example employees can access the company information by using username and password

EXTRANET

- An extranet is a private computer network which allows partner/vendors/customer
or suppliers to access part of its intranet.
- Also need username and password to access the company information
- Example such as an online banking application managed by one company on behalf of
affiliated banks

TYPES OF NETWORKS TOPOLOGIES

Types of network topologies

BUS TOPOLOGY

A bus topology consists of a single central cable called the backbone to which all computers and other devices connect. It acts as the main physical pathway or central cable where all other devices are connected. All nodes share the backbone to communicate with each other on the network. Sometimes, a bus network has more than one server. Sometimes, a server is not needed on the network.

The bus transmits data, instructions, and information in both directions. When the sending device transmits data, the address of the receiving device is included with the transmission so that data is routed to the appropriate receiving device.

An advantage of the bus network is that computers or other devices can be attached or detached at any point without disrupting the network. If one of the nodes fails, the transmission simply bypass the faulty device and the bus network would still function as long as the backbone is working. Other advantage include easy implementation and extension, comparatively cheaper since the use of cable is minimal, able faults are easily identified.

The disadvantages however are due to limited cable length and number of stations, if there is a problem with the cable, the entire network fails, maintenance cost is higher in the long run, performance degrades as additional computers are added or with heavy traffic and proper termination is required.

RING TOPOLOGY

A ring topology consists of all computers and other devices that are connected in a loop. Ring topology is also known as a ring network. In a ring network each node directly connects to two neighbouring nodes. Data transmitted on the ring network travels from device to device around the entire ring in one direction only.

When a computer or device sends data, it will travel to each computer in the ring network until it reaches its destination. If a computer or device in the network fails, all devices before the failed device are unaffected, but thos after will not function. The ring network can span a larger area than a bus network but is more difficult to install.

A server may exist in a ring network, but it will not connect to all the nodes in the network. The server, like other nodes, will only communicate to its two neighbouring nodes. This type of topology is primarily used for LANs but can also function in WANs.

The advantages of this type of topology are :- minimal cable requirement, no wiring cabinet or closet needed, message can be automatically acknowledge, no data collision between nodes.

The disadvantages include network failure if any nodes goes down, troubleshooting is difficult because of the one way communication and the number of nodes and distances are limited.

STAR TOPOLOGY

In a star network, every node or devices are connected to a central device, usually a hub, that provides a common connection for the nodes.

All data transfers from one node to another will go through the hub. Data travels in both directions. Every node must connect to the hub in order to communicate. If one of the nodes fails, the star network can still function as long as the hub is working.

A star network is easier to install and maintain but it need more cables. Nodes can be added or removed from the network without disrupting the network. In other words is one node or device fails the network will not be affected. But if the hub fails the entire network will be down.

The advantages of this topology are :- its easy to install and set up, easy to detect or remove faulty devices, network is not affected by failed devices, easy to expand( add more nodes), easy to troubleshoot since the problems can be isolated and is more suited for a larger network.

The disadvantages are : - failure of central hub will result in network failure, cost more compared to bus or ring topologies and it requires more cable

SOFTWARE - Operating System (OS)

Types of Operating System (OS)

Operating system is a set of programs containing instructions that coordinate all the activities among the computer hardware resources. Most operating system performs similar functions that include starting booting a computer, managing memory and configuring devices. Some operating system also allow user to control a network and administer security measures.

• Stand-alone OS – WinXP, Windows Vista, Mac OS, Linux, Dos
• Networking Operating System (NOS) – Windows NT, Windows Server 2000, Linux, Unix, Solaris
• Embedded Operating System – Windows CE, Palm OS, Symbian OS, Embedded Linux.

Platforms For Operating System

PC Platform Operating Systems - The examples of operating systems used on PC platforms or IBM compatible computers are DOS used a command line interface when Microsoft first developed it. Microsoft Windows XP’s operating environment is a Graphical User Interface (GUI). Both are closed source software.

Apple Platform Operating Systems - The operating systems used on Apple platforms are Mac OS & Mac OS X. Mac OS was the first commercially successful graphical user interface. It is a closed source software and are targeted for use with home desktops and workstations. Mac OS X is a multitasking operating system and targeted for use with home desktops, workstations and servers. It also has better security protection compared to Mac OS, for example the integrated firewall utility.

Cross-Platform Operating Systems - Cross-platforms operating systems are UNIX and LINUX. UNIX is a multitasking operating system. Some versions of UNIX have a command line interface but most versions of UNIX offer a graphical user interface. Linux is a popular, free, UNIX-like graphical user interface operating system. It is an open source software. Linux provides a great deal of liberty to those that interact with Linux technology. Although Linux runs on many kinds of equipment, it is best known for its support of IBM-Intel PC-based hardware.

The Main Functions Of OS

• starting a computer
• providing a user interface
• managing data & program
• managing memory
• configuring devices

Starting the Computer - The first function of an operating system is to start the computer. This process is called booting. Booting means to load & initialize the operating system. It can happen in two ways: warm boot or cold boot.

• A warm boot means restarting a computer that is already on. It normally happens after installing a new software or hardware or after an application crashes or stops working.
• A cold boot means starting a computer that is already off. It happens when we turn on a computer that has been completely powered off.

Providing a User Interface - This function controls how the user enters data and instruction and how information is displayed. The three type of user interface are Command-Line, Menu-Driven and Graphical User Interface . The user interface typically enables users:

• to start an application program
• to manage disks and files such as formatting, copying and renaming
• to shut down the computer safely by following the correct procedures

Managing Data & Programs - When we start an application, the CPU loads the application from storage into memory. In the early days, single-tasking operating systems could run only one application at a time. Multitasking operating systems enable users to work with two or more application programs at the same time.

Managing Memory - The computer's operating system is responsible for managing memory such as:

• optimizing the use of RAM
• allocating data & instruction to an area of memory while being processed
• monitoring the contents of memory
• releasing data & instructions from being monitored in memory when the process is done

Configuring Devices - Another function of an operating system is handling input and output, as well as enabling communication with input and output devices. Most operating systems come with drivers for popular input and output devices. These drivers install new devices and check whenever there is conflict with these devices.

Operating System Interface

The three type of user interface are Command-Line, Menu-Driven and Graphical User Interface.

COMMAND LINE USER INTERFACE

Command-Line User Interface

The command-line user interface requires a user to type commands or press special keys on the keyboard to enter data and instructions that instruct the operating system what to do. It has to be typed one line at a time.

It is difficult to use because it requires exact spelling, syntax or a set of rules of entering commands and punctuation. Complicated rules of syntax that specify exactly what you can type in a given place require memorization. It is also easy to make a typing mistake. The advantage of command-line interface is, it helps the user to operate the computer quickly after memorizing the keywords and syntax.

MENU DRIVEN USER INTERFACE

MENU DRIVEN USER INTERFACE

Menu-driven user interface enables the user to avoid memorizing keywords such as copy, paste and syntax. On-screen, menu-driven interface provide menus as means of entering commands. It shows all the options available at a given point in a form of text-based menu. Menu-driven user interfaces are easy to learn.

GRAPHICAL USER INTERFACE

Graphical User Interface (GUI) - GUI makes use of the computer’s graphics capabilities to make the operating system and programs easier to use, which is also called ‘user-friendly’. Today GUIs are used to create the desktop that appears after the operating system finishes loading into memory.

GUI is commonly used and has become a standard. It is easy to differentiate the interfaces between Mac OS, Windows XP or Linux by looking at their desktops. GUI with menus and visual images such as buttons, icons and other graphical objects to issue commands where many actions can be initiated by clicking icons that represent computer resources such as files, programs and network connections. On the desktop, we can initiate many actions by clicking the icons that represent the computer resources such as files, programs and network connections.

Differences Between Command-line Interface and Graphical User Interface

HARDWARE - Storage

Storage

Primary Storage (RAM, ROM) - Primary storage is the main memory in a computer. It stores data and programs that can be accessed directly by the processor. There are two types of primary storage which are RAM (Random-Access Memory) and ROM (Read-Only Memory). RAM is installed inside computers. RAM is also known as a working memory.

• Random-Access-Memory (RAM )- The data in RAM can be read (retrieved) or written (stored). RAM is volatile which means the programs and data in RAM are lost when the computer is powered off. Computer uses RAM to hold temporary instructions and data needed to complete tasks. This enables CPU to access instructions and data stored in the memory very quickly. RAM stores data during and after processing.
• Read-Only-Memory (ROM) - ROM is another type of memory permanently stored inside the computer. ROM is non-volatile. It holds the programs and data when the computer is powered off. Programs in ROM have been pre-recorded. It can only be stored by the manufacturer; once it is done, it cannot be changed. Many complex functions, such as start up operating instructions, translators for high-level languages & operating systems are placed in ROM memory. All the contents in ROM can be accessed and read but cannot be changed.

• 

Secondary Storage (magnetic medium optical medium, flash memory)

Secondary Storage is another alternative storage device to keep your work and documents. It is very useful to store programs and data for future use. It is installed externally. It is non-volatile, which means that it does not need power to maintain the information stored in it. It will store the information until it is erased.

Secondary storage can be divided into magnetic medium, optical medium and flash memory.

• Magnetic Medium - Magnetic medium is a non-volatile storage medium. It can be any type of storage medium that utilizes magnetic patterns to represent information. The devices use disks that are coated with magnetically sensitive material. The examples of magnetic storage are magnetic disk ( floppy disk, used for off-line storage, hard disk, used for secondary storage), magnetic tape ( video cassette, audio storage reel-to-reel tape & others)

• Optical Medium - Optical medium is a non-volatile storage media that holds content in digital form that are written and read by a laser. These media is usually a flat, circular portable disc which include various types of CDs and DVDs. These following forms are often commonly used:
• CD, CD-ROM, and DVD are a read-only storage, used for distribution of digital information such as music, video and computer programs.
• CD-R is a type of optical storage where it can be written once and cannot be erased or written over once it is saved.
• CD-RW, DVD-RW, and DVD-RAM allow data that have been saved to be erased and rewritten It is however slow to write but fast reading type of storage.

The disk capacity of optical media is more compared to magnetic media. Durability is another feature of optical media; they are able to last for up to seven times as long as traditional storage media.

• Flash Memory - Flash Memory is a solid-state, non-volatile, rewritable memory that functions like RAM and a hard disk drive combined. Flash memory store bits of electronic data in memory cells just like DRAM (Dynamic RAM), but it also works like a hard disk drive that when the power is turned off, the data remains in the memory. Flash memory cards and flash memory sticks are examples of flash memory.

Flash memory cards are also used with digital cellular phones, MP3 players, digital video cameras and other portable digital devices. Flash memory is also called USB drives, thumb drives, pen drives or flash drives, are the up-and-coming players in the portable storage market.

The advantages of flash memory are, it offers faster reading or access time compared to other secondary storage devices, (though not as fast as RAM) it is durable and requires low voltage. It is also light and small. The disadvantage is it is more expensive than the magnetic disk of the same capacity.