GSM (Global System For Mobile Communications)

GSM network is designed by using digital wireless technology. It offers compatible wireless services to all mobile users in all over the world. The basic requirements for GSM are following:

• Services
• Quality of services and security
• Radio frequency utilization
• Network

Services: The services, which are provided by the system, should be potable to all Mobile Stations or Mobile Phones so that it can b used in all over the world.

Quality of services and security: The quality of both voice and data services of GSM should be good. The voice data is encoded in digital form by using a modulation technique i.e.Gussian Minimum Shift Keying (GMSK).The security features should be provided by the system to protect the network against unauthorized users.

Radio frequency utilization: The system should use the available band of frequencies (For uplink: 890-915MHz & For downlink: 935-960MHz) efficiently.

Network: Network designers manage the identification and numbering plans while switching and mobility management based upon signaling system i.e. Signaling System Number 7(SS7).

GSM Architecture

The main component groups of GSM architecture are:

• Mobile Stations (MSs)
• Base Station System (BSS)
• Network and Switching Subsystem (NSS)

Mobile Stations (MSs):

The Mobile Station (MS) consist of two operational parts.

1. Mobile Equipment (ME)
2. Subscriber Identity Module (SIM)

Mobile Equipment (ME): This is the hard ware used by the subscriber to access the network and it has a unique identity number known as International Mobile Equipment Identity (IMEI).

Subscriber Identity Module (SIM): This is a type of electronic card that is plugs into ME and contains detailed information about the mobile subscriber.

Base Station System (BSS):

BSS is central equipment, which is located at the cell site. It provides the link between MS and NSS. The BSS consists of two operational parts.

Base Transceiver Station (BTS): BTS consists of transmitting and receiving antennas and signaling equipment that provide air interface for a cell to route the call. BTS communicates with the MS.A single BTS can support one or more cells.

Base Station Controller (BSC): All switching functions, which are performed in MSC, are controlled by BSC. It also supports handoff strategies and allocate or release temporary channels for those users whose needed handoff. Several BTSs can be controlled by a single BSC and one MSC can serve many BSCs

Network Switching Subsystem (NSS)

It is the main switching center of GSM network. NSS includes the following:

Mobile Switching Center (MSC): It is the basic unit of NSS, which supports call-switching or routing functions. Its purpose is the same as that of telephone exchange but due to advanced wireless technology, its working is much better than that of exchange. Each MSC provides coverage to a defined geographic area only.

Home Location Register (HLR): For subscriber its a reference data base. Current location of MS, identification numbers and various addresses are maintained in it.

Visitor Location Register (VLR): It's also a type of database. When an MS moves from home location to a visited location then its location is registered as a visitor in the VLR of visited system and this information is also updated in HLR of MS, by the VLR.

Equipment Identity Register (EIR): Its again a type of database, which contains information about MS equipment and check and identify its international validity of hardware and software to work properly.

Authentication center (AUC): Its a processing center and is normally worked together with HLR.Like HLR its also require to continuously access or update subscribers data. Its main purpose is to provide data security features to authenticate the subscriber.

VIRUS IN COMPUTER

A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. However, the term "virus" is commonly used, albeit erroneously, to refer to many different types of malware programs. The original virus may modify the copies, or the copies may modify themselves, as occurs in a metamorphic virus. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive. Additionally, viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan horses. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a file that appears harmless until executed.

How a Computer Virus Works?

The mechanism of a computer virus can undoubtedly be compared with working of a biological virus. Both of them more or less work in a similar way but follow different analogy.Unlike the computer virus, a biological virus is a fragment of genetic code, DNA, which breathes inside a human body and infects living cell by spreading rogue DNA into the cell environment. The viral DNA keeps replicating itself in the cell’s existing machinery.

Likewise, the computer virus seeks for a host i.e. any program or document to infect a machine and replicates itself each time a user opens the program. When the user opens an infected program, the virus loads itself into the computer’s memory and searches for another host to reproduce, thereby creating a vicious circle for itself.

Several viruses were originally designed to infect the boot sector, the part of the operating system that loads at the time you switch on your computer. The boot sector helps the computer in loading the operating system. By putting code in the boot sector, the virus is active every time the user switches on the computer.

General modes of computer virus transmission are infected floppy discs or documents uploaded to bulletin boards. All viruses have a sole aim to ruin computers’ functionality which is the main part of the attack phase. When the virus is being activated, a small program is opened to perform a task. It can be an attractive message on the user’s screen or it may attempt at deleting all the data present on your hard disk drive.

Immediate computer virus repair is must to avoid damage to computers. There are some terrible viruses that are always ready to scour the network’s functionality, thereby making it crucial to avail virus support. With technical support services have become the next big thing and arrival of names like IBM, Dell, iYogi, and Circuit City, the task of removing computer viruses can be done in no time.

Many personal computers are now connected to the Internet and to local area networks, facilitating the spread of malicious code. Today's viruses may also take advantage of network services such as the World Wide Web, e-mail, and file sharing systems to spread, blurring the line between viruses and worms. Furthermore, some sources use an alternative terminology in which a virus is any form of self-replicating malware.

Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.

VLSI (Very Large Scale Integration)

Very-large-scale integration (VLSI) is the process of creating integrated circuits by combining thousands of transistor-based circuits into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. The term is no longer as common as it once was, as chips have increased in complexity into the hundreds of millions of transistors.
The first semiconductor chips held one transistor each. Subsequent advances added more and more transistors, and as a consequence more individual functions or systems were integrated over time. The first integrated circuits held only a few devices, perhaps as many as ten diodes, transistors, resistors and capacitors, making it possible to fabricate one or more logic gates on a single device. Now known retrospectively as "small-scale integration" (SSI), improvements in technique led to devices with hundreds of logic gates, known as large-scale integration (LSI), i.e. systems with at least a thousand logic gates. The same process led to ICs with thousands of devices, becoming LSI. Current technology has moved far past this mark and today's microprocessors have many millions of gates and hundreds of millions of individual transistors.
As at mid 2006, billion-transistor processors are just on the horizon, with the first being Intel's Montecito Itanium Server. This is expected to become more commonplace as semiconductor fabrication moves from the current generation of 65 nm processes to the next 45 nm generations.
At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like Ultra-large-scale Integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use. Even VLSI is now somewhat quaint, given the common assumption that all microprocessors are VLSI or better.

PROGRAMMABLE LOGIC CONTROLLER

A programmable logic controller (PLC), or programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.

PLCs are well-adapted to a range of automation tasks. These are typically industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. PLCs contain input and output devices compatible with industrial pilot devices and controls; little electrical design is required, and the design problem centers on expressing the desired sequence of operations in ladder logic (or function chart) notation. PLC applications are typically highly customized systems so the cost of a packaged PLC is low compared to the cost of a specific custom-built controller design. On the other hand, in the case of mass-produced goods, customized control systems are economic due to the lower cost of the components, which can be optimally chosen instead of a "generic" solution, and where the non-recurring engineering charges are spread over thousands of sales.
For high volume or very simple fixed automation tasks, different techniques are used. For example, a consumer dishwasher would be controlled by an electromechanical cam timer costing only a few dollars in production quantities.
A microcontroller-based design would be appropriate where hundreds or thousands of units will be produced and so the development cost (design of power supplies and input/output hardware) can be spread over many sales, and where the end-user would not need to alter the control. Automotive applications are an example; millions of units are built each year, and very few end-users alter the programming of these controllers. However, some specialty vehicles such as transit busses economically use PLCs instead of custom-designed controls, because the volumes are low and the development cost would be uneconomic.
Very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls.
PLCs may include logic for single-variable feedback analog control loop, a "proportional, integral, derivative" or "PID controller." A PID loop could be used to control the temperature of a manufacturing process, for example. Historically PLCs were usually configured with only a few analog control loops; where processes required hundreds or thousands of loops, a distributed control system (DCS) would instead be used. However, as PLCs have become more powerful, the boundary between DCS and PLC applications has become less clear-cut.

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