Virus

A program or piece of code that is loaded on to your computer without your knowledge and runs against your wishes.Like any other program,it contains instructions that tell your computer what to do.

·         Viruses can also replicate themselves.

·         All computer viruses are manmade.

·         A simple virus that can make a copy of itself over again is relatively easy to produce.

·         A virus can be very destructive; it could format your hard drive, overwrite your hard drive boot sector, or delete files and render your machine inoperable.

·         Even such a simple virus is dangerous because it will quikly use all available memory and bring the system to a halt.

·         An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security sytems.


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GSM

                         Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 82% of the global mobile market uses the standard.[1] GSM is used by over 3 billion people across more than 212 countries and territories.[2][3] Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signalling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system.

                         The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM[4]). GSM also pioneered a low-cost, to the network carrier, alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112[5]. This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.

Private IP Address

                       The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets (local networks):

10.0.0.0 - 10.255.255.255

172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

These IP's should not be used on the Internet.

                 I usually use 192.168.0.1, 192.168.0.2, etc. and a subnet mask of 255.255.255.0 when assigning static IP addresses to computers on a small Local Area Networks (LANs).  If a DHCP server is also on the LAN it's scope (range of IP addresses that it can assign to computers on the LAN set to obtain their IP addresses automatically) should be adjusted so it does not interfere with locally assigned static IP addresses.

Wearable Computers

           Computer technology has played an important role in businesses throughout the years. There has been active development of increasingly portable computer hardware.The development originated with desktop and laptop units and is becoming increasingly apparent in palmtop, handheld and now wearable computers.

Sometimes the location of a desktop or laptop computer is inconvenient or inefficient. When accurate information is not available in a timely manner, production decreases. This is a problem for many businesses throughout the world. With rising costs and and demand for increased efficiency, wearable computers give  personnel real-time access to critical information.

The wearable computer provides the ultimate in network access-- hands-free, heads-up operation with complete mobility and ample computing power. Now personnel can connect to enterprise information systems without interrupting their work. With the convenience of voice activation and head-mounted or touchscreen display options, they can meet their ever-broadening responsibilities, supported by immediate access to on-line manuals, catalogs, parts  list, drawings, supplier information, work forms etc.

Input Devices

            Input devices enable data to be fed the computer in a from that the computer can use.Input devices are categorized into two types.

            1. Keyboard entry devices

            2. Direct entry devices

A device through which data can be entered to the computer by pressing keys is called a keyboard entry device whereas all the other types of input devices are called direct entry devices.

Keyboard

           The keyboard is the most commonly used input device and has been used since computers were first introduced.They are intelligent devices and contain their own chips.Each key is a switch,which closes when that particular key is pressed.The microprocessor scan the keyboard hundreds of times a second to see if a key has been pressed; if it has,a code that corresponds to that key is sent to the Processing Unit.The CPU then translates this code into the ASCII code (the code that computers use to represent charaters on the computer keyboard), which is the used by the computer program.

Mouse

             Mouse movements on the desktop are translated into digital information,which in turn is fed to the computer,causing the cursor to move on the screen.Underneath the mouse there is a ball which rotates when the mouse is moved by the user and sensors pick up this movement.A mouse usually has two or three buttons,and these are used to make selections on the screen.

                                                   

Microphone

             A microphone can be used to record sound into a computer.Microphones are also used for voice communication through a computer.

Camera

                   Digital cameras store the images digitally rather than on film.Digital still cameras can be connected to a computer and the pictures taken on them can be transferred while digital motion cameras or web cams can be used to create video and for video conferencing purposes.

                             

Scanner

                 Scanner are input devices normally used to scan pictures.The scans are then stored in a computer’s memory where they can then be accessed and modified using a desktop publishing package,befor being printed.Both black and white,and colour scanners are available.

NetWork Topology

Star Topology

            In a star network all computers and other communications devices are connected to a central point such as a hub, file server or a host computer.

Ring Topology

                 In a Ring network all communications devices are connected in a continuous ring. Messages are passed around the ring until they reach the right destination.

Bus Topology

               In a bus network communications devices are connected to a common channel. There is no central computer and the communications devices transmit messages to the other devices.

Mesh Topology

 

Networks

Network

                 A network is a collection of entities that exchange information or goods.A few examples of networks are railway system, nervous system of animals, telephone system.

Computer Network

               A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs),exchange files, or allow electronic communication.The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

            A communications network is a system of interconnected computers, and communication devices that can communicate with one another and share resoureces. At the most elementary level, a computer network consists of two computers connected with each other by a cable to allow them to share data.A device connected to a network is called a node.A node may be a device such as a computer, a printer, workstation etc.

Local Area Network (LAN) - 

                   LANs are networks usually confined to a geographic area, such as a single building or a college campus. LANs can be small, linking as few as three computers, but often link hundreds of computers.

Metropolitan Area Network (MAN) –

                  MAN is basically a bigger version of a LAN and normally uses similar technology. It might cover a group of near by corporate offices or a city and might be either private or public.

Wide Area Network (WAN) –

                 Often a network is located in multiple physical places. Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services.

WiFi

                  WiFi, wireless fidelity is the way to connect devices together without wires.  It can be done in homes, businesses, between businesses etc.  WiFi offers a lot of advantages over LANS, but it does include disadvantages. 

HOW DOES IT WORK

                  Wireless Internet Access has four components that form its structure: high-speed access, a networking gateway, a wireless network and a wireless customer.  The customer connects wirelessly through the wireless network to the gateway, it then launches their internet browser, authenticates through the gateway by entering a coupon code or purchasing time and the user has high-speed internet.

The four components are:

1)High-speed access which is also known as broadband is an internet connection which is generally faster than dial up service.  Examples of high-speed internet access are ISDN, cable modem, DSL, and also  satellite services.

2) Network Gateway is between your high-speed access connection and the wireless network, it acts like a gate.  This gate will prevent people from accessing your wireless network unless you know about it, the gateway also allows managing tools as well.  These can include authentication, network monitoring, and other services such as printing and voice over IP. 

3) Wireless local area network is a system of connecting PC's and other devices within the same physical proximity using high-frequency radio waves instead of wires.  Wireless networks work as long as your wireless ready device is within range.

4) Wireless customers are people who have a PC and a wireless adapter which means they can access the internet wirelessly.  The wireless adapter can be built in or it can be an external device plugged into your computer. 

WiFi, allows a universal internet connection to be bordercast through radio waves.

                    Radio waves are what make WiFi exist and run.  They allow WiFi networking to occur between numerous people.  The radio waves are transmitted from antennas and routers and are picked up by WiFi receivers such as computers and cell phones equipped with WiFi cards.  When these devices receive a signal within the range of a WiFi network, the WiFi card then reads the signals and produces an internet connection without a cord.   Once a connection is established between user and the network , the user will be prompted with a login screen and password if it is fee based.

                  WiFi networking around the world is creating not spots in the cities where anyone with a laptop can wirelessly plug into the internet.  Hot spots are connection points for WiFi networks; areas where wireless internet is available for those who have internet ready devices.  Hot spots are becoming available everywhere, in restaurants, hotels, airports, schools, etc.

               The following is a simple and understandable way to picture the way WiFi works.  The main source is the antenna; the antenna sends radio signals to the people who want to access the internet.  The people wanting access must have a Wife card; the Wife cards receives the radio signals through its' Wife receivers and creates a wireless connection.

Web Servers
                     Web servers are computers that deliver (servers up) Web pages.Every web servers has an IP address and possibly a domain name. For example, if you enter the URL http://www.news.lk/index.html in your browser, this sends a request to the web server whose domain name is news.lk. The server then fetches the page named index.html and sends it to your browser.
                      Any computer can be turned into a web server by installing server software and connecting the machine to the Internet. There are many web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others.

Tsunami Alarm System 

              The hazards that originate from tsunamis have been recognized for some time. Newspaper reports about undersea earthquakes and movies about meteor-inflicted tsunamis have contributed to public awareness of the threat. Early warning systems were constructed and deployed for instance in the Pacific Rim. Many areas in the world, however, are not covered by traditional warning systems.At the latest in December 2004, when a tsunami has devastated wide areas bordering to the Indian Ocean, the extensive media coverage has elevated the sheer possibility, the effects and the dangers of a tsunami into global public consciousness.In the memory and perception of tourists and holidaymakers seashore sites may forever bear tsunami-related dangers, resulting   in the desire for effective,reliable and easy-to -use tsunami alarm systems.

                     Our Tsunami alarm system contributes to alleviate this problem and has been filed for patent protection. The Tsunami Alarm System has recently been introduced into the market and users can now subscribe. Subscribers to this alarm system will reliably receive an alarm to their mobile telephones, as and when a dangerous tsunami is evoked. In this way the invention enables people to take preventive action many minutes before the devastating tsunami arrives.

ISP

ISP stands for Internet Service Provider, a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mails. In addition to serving individuals, ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs). ISPs are also called IAPs (Internet Access Providers).

GPS

            "Standalone" or "Autonomous" GPS operation uses radio signals from satellites alone. A-GPS additionally uses network resources to locate and utilize the satellites in poor signal conditions. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or be weakened by passing through atmospheric conditions, walls or tree cover. When first turned on in these conditions, some standalone GPS navigation devices may not be able to work out a position due to the fragmentary signal, rendering them unable to function until a clear signal can be received continuously for up to 12.5 minutes (the time needed to download the GPS almanac and ephemeris).

An Assisted GPS system can address these problems by using data available from a network. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.

Assistance falls into two categories:

1). Information used to more quickly acquire satellites

·         It can supply obital data or almanac for the GPS satellites to the GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases.

·         The network can provide precise time.

2). Calculation of position by the server using information from the GPS receiver

·         The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position.

·         The assistance server has a good satellite signal, and plentiful computation power, so it can compare fragmentary signals relayed to it

·         Accurate, surveyed coordinates for the cell site towers allow better knowledge of local ionospheric conditions and other conditions affecting the GPS signal than the GPS receiver alone, enabling more precise calculation of position. (See also Wide Area Augmetation System)

As an additional benefit, in some A-GPS device implementations, known as "MS-Assisted," the amount of CPU and programming required for a GPS receiver is reduced by offloading most of the work onto the assistance server.

A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for aGPS information. If it also has functioning autonomous GPS, it may use standalone GPS, which is sometimes slower on time to first fix, but does not depend on the network, and therefore can work beyond network range, and without incurring data usage fees.^[Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.

Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System and cell-site triangulation and sometimes a hybrid positioning system.

High Sensitivity GPS is an allied technology that addresses some of these issues in a way that does not require additional infrastructure. However, unlike some forms of A-GPS, high-sensitivity GPS cannot provide a fix instantaneously when the GPS receiver has been off for some time.

Basic concepts

Standalone GPS provides first position in approximately 30-40 seconds. A Standalone GPS system needs orbital information of the satellites to calculate the current position. The data rate of the satellite signal is only 50 b/s, so downloading orbital information like ephemeris and almanac directly from satellites typically takes a long time, and if the satellite signals are lost during the acquisition of this information, it is discarded and the standalone system has to start from scratch. In AGPS, the Network Operator deploys an AGPS server. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM,CDMA, WCDMA,LTE or even using other wireless radio bearers such as Wi-Fi. Usually the data rate of these bearers is high, hence downloading orbital information takes less time.

 Modes of operation

AGPS has two modes of operation:

1.       Mobile Station Assisted (MSA) - In MSA mode A-GPS operation, the A-GPS capable device receives acquisition assistance, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and sends the measurements to the A-GPS server. The A-GPS server calculates the position and sends it back to the A-GPS device.

2.       Mobile Station Based (MSB) - In MSB mode A-GPS operation, the A-GPS device receives ephemeris, reference location, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and calculates the position.

Standards

AGPS protocols are part of Positioning Protocol defined by two different standardization body,3gpp and Open Mobile Alliance(OMA).

1). Control Plane Protocol - It is defined by 3gpp for various generations of mobile phone system. These protocols are defined for Ciucuit Switched Networks. Following positioning protocol has been defined.

1. 1.       RRLP - 3gpp defined RRLP or Radio resource location protocol to support positioning protocol on GSM networks.
2. 2.       TIA 801 - CDMA 2000 family defined this protocol for CDMA 2000 networks.
3. 3.       RRC position protocol - 3gpp defined this protocol as part of the RRC standard for UMTS network.
4. 4.       LPP - 3gpp defined LPP or LTE positioning protocol for LTE Networks.

2). User Plane Protocol - It is defined by OMA to support positioning protocols in Packet Switched  Networks. Two generations of User plane Protocol have evolved.

1. 1.       SUPL V1.0
2. 2.       SUPL V2.0

Printers

                             A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work.

Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. There are two other types of page printers that fall under the category of laser printers even though they do not use lasers at all. One uses an array of LEDs to expose the drum, and the other uses LCDs. Once the drum is charged, however, they both operate like a real laser printer.

                     One of the chief characteristics of laser printers is their resolution -- how many dots per inch (dpi) they lay down. The available resolutions range from 300 dpi at the low end to 1,200 dpi at the high end. By comparison, offset printing usually prints at 1,200 or 2,400 dpi. Some laser printers achieve higher resolutions with special techniques known generally as resolution enhancement.

                         In addition to the standard monochrome laser printer, which uses a single toner, there also exist color laser printers that use four toners to print in full color. Color laser printers tend to be about five to ten times as expensive as their monochrome siblings.

Laser printers produce very high-quality print and are capable of printing an almost unlimited variety of fonts. Most laser printers come with a basic set of fonts, called internal or resident fonts, but you can add additional fonts in one of two ways:

·         font cartidges : Laser printers have slots in which you can insert font cartridges, ROM boards on which fonts have been recorded. The advantage of font cartridges is that they use none of the printer's memory.

·         soft fonts : All laser printers come with a certain amount of  RAMmemory, and you can usually increase the amount of memory by adding memory boards in the printer's expansion slots. You can then copy fonts from a disk to the printer's RAM. This is called downloading fonts. A font that has been downloaded is often referred to as a soft font, to distinguish it from the hard fonts available on font cartridges. The more RAM a printer has, the more fonts that can be downloaded at one time.

                          In addition to text, laser printers are very adept at printing graphics. However, you need significant amounts of memory in the printer to print high-resolution graphics. To print a full-page graphic at 300 dpi, for example, you need at least 1 MB  of printer RAM. For a 600-dpi graphic, you need at least 4 MB RAM.

Because laser printers are nonimpact printers, they are much quieter than dot-matrix or daisy-wheel printes. They are also relatively fast, although not as fast as some dot-matrix printers. The speed of laser printers ranges from about 4 to 20 pages of text per minute   (ppm). A typical rate of 6 ppm is equivalent to about 40 characters per second (cps).

Laser printers are controlled through page description languages(PDLs). There are two de facto standards for PDLs:

·         PCL : Hewlett-Packard (HP) was one of the pioneers of laser printers and has developed a Printer Control Language (PCL) to control output. There are several versions of PCL, so a printer may be compatible with one but not another. In addition, many printers that claim compatibility cannot accept HP font cartridges.

·         PostScript : This is the de facto standard for Apple Macintosh printers and for all  desktop publishing systems.