a2 ict g063 revision guide

Thomas Roe13B/It1Mr. Moore

The Systems Life CycleThe stages of the systems life cycle are as follows:1. Definition2. Feasibility3. Investigation4. Analysis5. Design6. Implementation/Installation7. Introduction/Development8. Testing9. Monitor/Evaluate10. Maintenance11. Documentation

Systems Life Cycle task

Jack Cornwall College is considering replacing it’s computer network. The present hardware/software that the College has is - two server computers running Windows server 2000, multiple workstations running Windows 98 and Microsoft Office 2003. The servers do all the basic network functions (i.e.) file and print serving, e-mail, internet connection etc.

Using this scenario show how structured system analysis and design would help the College to bring in a new system. This is called the SYSTEMS LIFE CYCLE.

1. Definition of Problem2. Feasibility study3. Investigation4. Analysis5. Design6. Implementation/Installation7. Introduction and Development 8. Testing9. Monitoring and Evaluation10. Maintenance11. Documentation

Write a short paragraph to describe how the College should go through each step in the cycle to successfully bring in a new system.


The college should firstly, define the problem (i.e. replace the computer network) and identify the software/hardware currently in use.Feasibility should be included within the following considerations: Cost User friendliness Complexity Time Skills needed Hardware/Software required Training

It is best for the college to completely revamp their system, in my opinion as it improves their performance by 70%.

The system should then be investigated for potential upgrades, software purchases and software that can be kept in the future.

However, the software that needs to be bought must meet the requirements set by the end-user and the design must reflect that by designing interfaces that uses the newly bought hardware and software in their plans. Key parts, such as the validation methods and the user interfaces must be implemented and tested, still keeping the customer requirements in mind.

After all of this, they must install the software, if everything goes to plan with the software and hardware.They can choose to directly install (switch on, switch off), parallel install (run both), phase the install (install in small chunks) or pilot the install (new system installed and tested in parts).

User documentation then needs to be developed to show potential users and technicians how to use the system and how to repair any faults or answer any questions that may need to be asked. This can also be done on-screen.

When all of this is done, the evaluation must be performed. Did the software meet the customer’s requirements? If not, this must be checked out.

Maintenance of the software can be done in 3 ways.Corrective maintenance involves identifying problems after the install process.Adaptive maintenance involves strategic or methodology changes.Perfective maintenance involves addressing minor tweaks bought up by customers.


Investigative ApproachesThere are 4 types of approaches that can be taken to investigate a system. These are:1. Document Analysis2. Questionnaires3. Interviews4. Participant Observation

All of these methods have their own consideration factors and their own advantages and disadvantages. I will go through each one in turn and state some of the advantages and disadvantages of each method.

An analyst has been given the job of finding out the shortcomings in the old system and producing a set of requirements for the new system. He is unsure of the investigative methods available to him in order to carry out this work.

Describe the advantages and disadvantages of each of the following in a report and recommend two methods that are best suited to this situation

1. Document Analysis 2. Questionnaire 3. Interviews 4. Participant Observation 5. Meetings

Document AnalysisThis can use any paper-based document such as receipts, invoices and reports.

Data types and formats can be examined in each document and they can be useful for inefficient data flows.

However, they cannot capture the efficiency of the data collection and the analyser cannot understand how the document was used.

QuestionnairesQuestionnaires are useful to gather information from people. However, there are a lot of factors that need to be taken into consideration to ensure that the questionnaire can extract useful information.

Open and closed questions can be used in questionnaires. Open questions allows for expansion on answers.

Consideration factors include quantity (people do not want a 20 page document), wording (they need to be able to understand the question) and presentation (clarity is important here).

Thomas Roe13B/It1Mr. MooreEveryone can be asked the same questions in a questionnaire, lots of data can be collected and the questionnaire can be planned ahead.

However questionnaires are impersonal and closed questions cannot be expanded upon. Also, the questionnaire is only as good as the questions in it.

InterviewsThe questions in interviews are usually open and focus in on certain factors. 3 types of interview can be performed.1. An initial interview (to scope the problem)2. A interview involving gathering the facts3. A final interview, when the drafts have been completed.

With interviews, personal contacts can be achieved and extra detail can be added. It can also be planned in advance.However, there are time limits, practicality limits and the interview must be well-structured in order to get a successful interview.

Participant ObservationThe factors to consider when observing participants involve how tasks are completed, how long tasks take and any delays or problems that may be encountered when carrying out the tasks.

Observation can be direct or indirect. Direct observation involves someone sitting next to the person and watching them do the task. It gives the observer a chance to ask questions. Indirect observation involves video cameras and the recording of footage of the task being performed.

With participant observation, inefficiencies are spotted, timescales are measured and persistent problems are identified. However, it is not efficient at quantitative (numerical) data, people do not like being watched and there are time constraints.

In conclusion, if I was to choose 2 methods that were best suited to this analyst, I would probably want him/her to give questionnaires and to interview people face to face to find out what is exactly required for the new system and to gain a wide range of opinions.


Software Development Approaches

Investigate the following questions adding your answers to your notes.

Describe the evolutionary and throw-away prototyping methodologies in your own words.

Describe the RAD methodology.

Investigate software systems that could be developed using the prototyping methodology.

What is “prototyping?”

Prototyping is an “iterative” process and a system that uses prototyping is not a fully working one.

There are 2 different types of prototyping, evolutionary prototyping and throw-away prototyping.

Evolutionary Prototyping

Evolutionary prototyping involves feedback and comments from the user after each stage and developing it further. The prototype is incorporating the changes made and as a result, it evolves into the finished product.

Advantages of this are that the delivery is quick, the user interacts a lot with the system and it is tailored to the user’s requirements.

However, there is no knowledge of when to stop tweaking and start finishing the prototype.

Throw-Away Prototyping

Throw-Away prototyping involves developing a small part of the system, evaluating the small part and throwing away the old prototype. This ensures that all of the customer requirements are met and it reduces the risk of poorly defined requirements.

The throw-away prototype focuses the user on one part of the system, however, developers may be forced by the user to make the final system and all of the work of putting together a prototype will be lost.


Prototyping – Pros & Cons

1. The system is of better quality2. Money is saves3. Training can be carried out4. Problems are identified in the early stages5. User requirements can be fulfilled6. The user feels more involved

1. Development time is too long2. The system can differ greatly from the prototype so users are confused.3. The development time can be greater if features are missing.4. There is too much focus on one part of the system.5. Constructing a prototype costs money (due to hardware and development time).

RAD – Rapid Application Development

Systems are developed faster under this process. This can be done by:

Workshops & Focus Groups – The user is actively involved and feels satisfied as he/she owns the project. There are fewer last minute changes and the requirements are much more detailed.

JAD (Joint Application Development) can be used to involve the user as much as the development team.

Prototyping – refining the system, heavy user involvement.

Strict Timescales – Each part of the requirements is like a “mini-project”. The requirements are divided into tasks, each with a set time limit. If one task is late, it can be added to another task, simplified or scrapped.

Re-using software components - This speeds up the delivery process using RAD and enables the existing software to be used to the maximum effect. This can be done by using software libraries, software classes or frameworks (complete environments with built in features).


RAD – Pros & Cons

1. The user is more involved.2. The requirements specification evolves over time.3. The project is sped up.

1. Not everyone is 100% satisfied.2. The system is not ideal for everyone.

A project that could be developed using the RAD methodology

User Input Screens

1. Initial prototype is made, tried out by users, immediate feedback given2. Requirements specification developed, developer changes interactions.3. Adjusted prototype tried out, feedback is given.4. The interaction is eventually accepted and signed off.5. A new prototype is released with all graphics correct, feedback is again given.6. The prototype evolves toward the finished system.


Testing & Test Plans

Factors Affecting Testing

There are 3 major factors that affect the quality of testing procedures.

The first factor is the critical nature of the system. The more important a system is, the more thorough the testing needs to be. For example, a customer records form would need to be tested thoroughly.

The second factor is the time available. The thoroughness of the job would be measures by the amount of time that is available to do the project. The project will be more thorough if testers had one month to test the system rather than one week.

There are other external constraints to deal with such as the fact that systems could have to meet legal requirements e.g. software features controlling systems in cars need to be tested to an industry-recognised standard. An external audit will take place to ensure everything has been tested properly and everything is working.

Selecting Tests

It is impractical to test everything in the system. The skill is in selecting a practical number of tests that can be done in the time available and to be confident the system is working.

The Testing Team

A team of testers can be chosen to test the system. BETA testers check the system does everything exactly as planned in the specification. This team can check if the system is ‘user-friendly’ but it is not their main role. A separate team is appointed, which is made up of front end users.

Test Data

Any testing checking validation procedures must include:

Normal data that lies in the specified range

Extreme data on the extreme limits of the range e.g. £50 should be tested if the rule is <=£50.

Erroneous data that should not be accepted e.g. <=£50 and entering p.

Test Plans

Test plans must be carried out and it is a detailed document which a team of testers follow carefully.

Every test is set out, data is entered and results are obtained.

The testing procedure should cover the requirements of the system, the performance of the system, the pathways in the system and the validation methods of the system.


The testing process involves people following the exact plan, entering the data, recording the observations and deciding whether the test passes or fails. If it passes, the next test is set up. If not, the developers work on the concerned area. The best people to test the system are real users as they will do things that the designers do not expect.

Iteration & Looping

Testing is an iterative process. The problems may be with the user requirements.


Requirements, Design and System Specification

There are 3 types of specification used in the design process.

User Requirements Specification – This is done at the end of the investigation & analysis stage and investigates the capabilities of the system.System Specification – This is done during the design stage and evaluates the technical detail of the system.Design Specification – This is done at the start of the design stage.

The user requirements spec needs to include: Scope Objectives Timing Constraints Inputs Outputs ProcessingThis is like a contract between the end user and the person delivering the project.

The design spec needs to include:

Purpose Screen Layouts/Style Templates Data Structures Input/Output/Processing Details Validation Rules Error Messages Modelling Diagrams (such as Entity Relationship Diagrams) Software/Hardware Requirements Test Plans

It is basically an outline of what needs to be done.

The systems spec needs to include:

Thomas Roe13B/It1Mr. Moore Software Applications Storage Requirements System Memory Requirements Input/Output Devices Processing/Computing Power required Security & Backup System Requirements Manpower Requirements Building & Office Requirements Network Configuration Requirements System Feeds Required

This is basically an outline of how the system is made.

The notable differences between the 3 specs is that they deal with different parts of the system and they are done in different stages in the design process.

Roles & Responsibilities within an IT Team

Thomas Roe13B/It1Mr. MooreProject Manager – Manage staff, plan project/staff training, co-ordinate problem solving, manage budget, documenting & processing.

Systems Analyst – meet with end user to decide on system, requirements, problems and processes.

Systems Developer – technical duties (design, planning, selecting, writing, producing), people duties (explaining to client, talking to other team members)

Programmer – Write codes and technical documentation for the new system.

Tester – Test the whole system and decide how to test it.

Project Planning

Thomas Roe13B/It1Mr. MooreThe reasons why a project fails is due to:

Poor planningPoor time managementOver optimism/unrealistic time framesPoor budgetary controlInsufficient budgetPoor communication within project team or users

This wastes time, money and company resources.

However, there are tools available that can help to rectify and prevent project failings in the future.

Gantt Charts are charts recording timescales. They record timescales on the horizontal axis and the activities are recorded down the side. The time taken for each task will be clearly shown by shading relevant boxes.

As can be seen, the bars show the amount of time each task should take, with the times on the horizontal axis and the activities on the vertical axis.

The times are shown, tasks are shown individually, the chart is set up like a calendar and the project can be completed easily with a Gantt chart. However, the charts can be too simplistic or huge on large projects, and there is a lack of critical paths.

This comes with Critical Path Analysis, which identifies each stage and the time allowed for it. Staff are employed to ensure they are not falling behind with the project.

The activities are identified and prioritised.The completed activities are identified.The earliest start time (EST) and latest finish time (LFT) is identified.The FLOAT is identified – tasks outside the critical path.

Thomas Roe13B/It1Mr. MooreThe critical path is identified.

Efficiency is increased, time scales are enabled, tasks are scheduled in a logical order, tasks are not held up and waste is reduced.

However, skilled people are needed, the usefulness is limited with complex and large project and accurate time estimates are needed.


8 – Critical Path Analysis

TasksPrimary Research – 1 weekInvestigation of the old systemQuestionnaire – 2 weeksMeetings – 1 week (dependant on the observations being completed)Observations – 3 weeksCreate the user requirements – 2 weeksCreate the design specification – 4 weeksDesign the systemDatabase (Entity Relationship Diagrams/Data flow diagrams) – 2 weeksFront end/User Interface – 3 weeks (dependant on the database being completed)Implement the system – 4 weeksTest the system – 2 weeksMeet with the user to check the system is fully operational and meets the user requirements – 2 week

Tasks Description Order/Logic TimePrimary Research Research task Do first 1 week

Questionnaire Investigate old system

After Research 2 weeks

Meetings Meet with client After Research 1 weekObservations Observe what

client doesAfter Research 3 weeks

Create user requirements

Create specification for

user

After Investigation 2 weeks

Create design specification

Create design template

After Investigation 4 weeks

Database (Entity Diagrams)

Start database After Analysis 2 weeks

User Interface Start User Interface After Analysis 3 weeksImplementation Implement the

systemAfter Design 4 weeks

Testing Test the system After Design 2 weeksMeeting with user Evaluate with user After

Implementation & Testing

2 weeks

Primary Research1 week

1A

Observation3 weeks

4D

Testing2 weeks

20/19/21

Implementation4 weeks

18/17/19

I

User Interface3 weeks

14/13/15

H

Design Specification4 weeks

9/8/10F

Database2 weeks

11/10/12

G

User Requirements2 weeks

5/4/6E

Questions2 weeks

3B

Meetings1 week

2C

Evaluation2 weeks

22/21/23



10 – Entity Relationship Diagrams

One-One Relationships

One to Many Relationships

Many-Many Relationships

AppointmentAppointmentID

DoctorDoctorID

PatientPatientID

TimeDateType

PatientPatientID

NameAddress Line 1Address Line 2

TownPostcodeDoctor

DoctorID

DoctorName

Address Line 1Address Line 2

TownPostcodeDoctorID


DoctorName

Address Line 1Address Line 2

TownPostcodeDoctorID

PatientPatientID

NameAddress Line 1Address Line 2

TownPostcodeDoctor

DoctorID

AppointmentAppointmentID

DoctorDoctorID

PatientPatientID

TimeDateType

Treatment/PrescriptionPatientIDPatientDoctorIDDoctorTreatment requiredFrequency

Diagnosis

Off

Dependent on burglar being present

Senses intruder

Alarm activated

When burglar is present

5-10 seconds


11 – Flowcharts & State Transition Diagrams

State transition diagrams represent something that occurs in different ways, such as traffic lights. They can be on red, red & amber, green, amber (and then back to red). Each of these modes is called a state and the transfer from one to another is called a transition event. The system can be transmitted as a state transition diagram.


3.3.2 – Designing Computer Based Information Systems

1 – Batch, Interactive & Real Time Processing Methods

L.O. Discuss batch, interactive and real-time in terms of processing methods, response time and user interface requirements.

Task One

1.) Give 3 examples of tasks that are not suitable for batch processing and give a number of distinct reasons why this is the case.

2.) Thinking about the 3 examples you have chosen, what type of processing method would be suitable? Why?

3.) Make a table with all three different types of processing methods. Make a column to write what kind of response times each has. What are their user interface requirements?

Batch processing is used when large quantities of data are to be collected together and treated in a similar way. The data is collected together before processing and the job is treated as a single unit with no human intervention. It is often run at night when there is slack time on the computer system and so results are not immediately available but can be scheduled to be used at an appropriate time. Typical uses include payroll, billing systems, multiple choice exam papers, etc.

Real-time processing is used when inputs need to be dealt with very quickly i.e. in real-time. This has to be programmed very carefully to ensure that nothing is missed off.

Examples include: traffic lights, heart rate monitoring, aircraft control, computer games and controlling robots e.g. remote control cars.

These examples cannot be used for batch processing because the inputs need to be dealt with instantaneously without any delays. Also, the inputs have to be done separately and humans have to provide the input before it is dealt with.

Interactive processing is also known as transactional processing and occurs when inputs are dealt with after a short delay (in terms of computer time, it may seem that the processing is done straight away). It may have spent the delay doing other things, such as booking concert tickets, ordering books online, handling bank accounts and booking a holiday. Interactive processing occurs one at a time. A GUI is the most common type of interface for interactive processing.

The user interface is very important with interactive processing. It must be clear, easy to use and very responsive. Data validation should take place to ensure all data is present, accurate and precise.


Processing Type Response TimeReal Time Instantaneous

Batch DailyInteractive/Transactional After short delay


2 – Operating Systems Learning Objectives

Describe the difference between types of operating systems (single-user, multi-user, multi-tasking, interactive, real time, batch processing and distributed processing systems) by identifying their major characteristics.

Operating Systems

An Operating System is a program written to make computers useable by people other than specialist engineers. You do not need to worry about how to write a character to the screen, how to print, how to load or save to disc, … Most Operating Systems are very complex – some of the most complex programs ever written

The Operating System directly interfaces with the computer’s architecture – think of the Operating System as a layer wrapped around the hardware. Most users interact with an application program such as a spreadsheet. You can think of these applications as another layer wrapped around the Operating System. The application program translates the user input/output into commands which the Operating System understands. The Operating System then translates these commands via machine code routines into a form which the hardware understands.

A large number of operating systems have been designed over the years, and they have all been set up with one specific computer or system in mind.

Windows/Linux – PCs

MacOS – Mac computers

Unix – Mainframe computers

Symbian, Android – Mobile phones

Common functions are: provision of a user interface, storage of computer memory and hardware.

Single User

2 types

Single Application – deals with one user at a time, e.g. mobile phone or iPad

Multi-tasking – deals with many applications running at the same time, whilst still being designed with the single user in mind e.g. Windows Vista, Windows 7, Linux, Mac OS X Leopard.

Thomas Roe13B/It1Mr. MooreDifferences – One handles a different amount of applications to the other and because of this, the memory available is expanded, commonly to Gigabytes.

Multi-User

Allows more than one user to log on and use the system at the same time with the computer and resources. It also allows people to multi-task and run many applications at one time.

The operating system has to manage the users, the allocation of resources, security, processing time and efficiency.

Another example would be a computer running a single user, multi-tasking operating system connected to a network, allowing it to share peripherals and documents.

Interactive

This allows the user to directly interact with the operating system while one or more programs or applications are running on the computer. This is common in most operating systems.

Real-Time

This type of operating system is designed to handle input data within a specific time frame (“latency”). This time could vary, depending on the type of application that needs to be run.

Batch

This operating system is set up to run “jobs” (i.e. input data files) without any user interaction at all.

The jobs consist of inputs, processing and outputs.

Distributed

This is where single tasks are split up into smaller components and they are worked on separate computers and gathered together at the end of the whole task. Distributed operating systems manage this process.


4 – Methods of Dialogue

Learning Objectives

- Compare and contrast different methods of dialogue that allow interaction between computer and person, person and computer, and computer and computer

Methods of Dialogue

There are four main features of interaction between a computer and a person:

o prompts o nature of input o methods of input o feedback

The type of dialogue is responsible for selecting the most appropriate method of dialogue to be used. The choice will depend on the investigations that have been completed, the tasks that the users need to complete and the requirements of the business.

Prompts

A prompt is most commonly used in a command line interface. It indicates that the user needs to input an appropriate command. When the command has been input the command line interface will then complete the required action. This type of dialogue can be difficult for 'every day' users to learn and so is best used for technical administration of the system.

Prompts can also be used in a graphical user interface (GUI). Unlike command line interface, a GUI uses icons to prompt the user. The icons should be intuitive and simple to use and represent a concept that is familiar to a user, such as a dustbin image for deleting or an X to close a window.

A menu-driven interface will, by nature of its characteristics, use menus to offer the user a selection of possible inputs to choose from.

Question - Describe how prompts could be used in a command line interface

Nature of Input

The nature of the input can also differ between interfaces. Interactive interfaces decide the nature of the next user input (e.g. by asking a question or by requiring a selection to be made) based on the response to the previous input.

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Thomas Roe13B/It1Mr. MooreForms might be used as the basis for the dialogue with those being displayed being decided by a pre-determined sequence of user inputs.

Method of Input

If the dialogue is being completed using a command line interface, then the usual method of input is a keyboard. The user will have no need for other peripherals. Form-based interfaces can also be used with only a keyboard, however it is often simpler to also use a mouse. Touch screens have become a popular method of input (e.g. on cash machines).

Question - Investigate other applications where the method of input is a touch screen

Feedback

Any dialogue must provide feedback. This could be in the form of menus that provide options for the user to select. A menu option may be a sub-menu giving further options, for example a designer might provide a general menu with sub-menus that provide specific areas or tasks that need to be carried out.

The feedback given in a real-time or interactive interface is a further set of required responses or the completion of the task providing the user with the required results. This type of feedback will give the user very specific and limited choices because the responses given to each set of questions of choices will limit the response given.

Mind Mapping Task

Read the following text and have a go at this using the text to the left hand side. There are also some questions in there for you to answer. Get creative!

Right now tens of thousands of students around the world are taking lecture notes in a completely inefficient way: writing them down line by line; or, in some languages, column by column.

But the brain does not work that way. It does not store information in neat lines or columns.

It stores information like branches on a tree – on branches called dendrites. It also stores information by patterns and associations. And to store information the way your brain does – British psychologist Tony Buzan has invented Mind Mapping.

Thomas Roe13B/It1Mr. MooreSo don't take notes, make Mind Maps. And make them with trees, with pictures, with colours, with symbols, with patterns and associations.

1. Imagine your brain cells are like trees, with each one storing related information on its branches.

2. Now try arranging the key points of any topic on a sheet of white paper in the same treelike format.

3. Start with the central topic – preferably with a symbol – in the centre of the page, then draw branches spreading out from it.

4. Generally record only one word and/or symbol for each point you want to recall – one main theme for each branch.

5. Put related points on the same main branches, each one shooting off like a new sub-branch.

6. Use different coloured pencils or markets for related topics. 7. Draw as many pictures and symbols as you can.


• Human Computer Interface• A term used to describe the interaction between the user and a computer.

The method by which the user tells the computer what to do and the responses which the computer makes

• Importance of good interface design• A good interface design ensures that users carry out their tasks• Safely – think of a pilot flying a jumbo jet• Effectively – operating a video recorder successfully to record the correct

program• Efficiently – users can obtain money from a cash machine, inserting card and

pin, obtaining cash and removing their card• Enjoyably – can use a computer program to learn tables, for example• Interface Styles• There are a number of interface styles including:• Command line interface• Menus• Natural Language• Forms and dialogue boxes• WIMP • Command Line Interface• Provides a means of expressing instructions to the computer directly using

single characters, whole word commands or abbreviations.• Very little help is given.• Commands enable a user to quickly and concisely instruct the computer what

to do• User requires the knowledge of the commands available and the syntax for

using them• Operates via DOS• Menu interface• Full screen menu – front end application use. Stays on screen until the user

makes a choice. Eg A switchboard on a database• Pull down menu – displayed along the top of a screen. When the user clicks

on an item, a submenu appears. Always present at the top of the screen whatever screen the user is looking at in the application.

• Pop-up menu – menu pops up due to a response, say, a click of the right mouse button on a particular area of the screen.

• Natural Language – “plain English”Advantages

• No need for training in a specialised command language• Extremely flexible and powerful• User is free to construct her own commands, frame her own questions, etc.

Disadvantages


• People find it difficult to stick to grammatical correct English• A well designed artificial language can say the same thing more concisely

than natural language• A natural language can mislead a user into believing the computer is more

intelligent than it actually is• Forms & Dialogue Boxes• A form is used to enter data, such as customers names.• A dialogue box is a special type of form, usually in the Windows environment,

for example, a form appears when a print job is set up to the printer.Points to consider when designing a form:-

• Should have a title to identify it• Not be too cluttered – space and blanks are important• Corrections should be allowed before the data is accepted• Items should appear in a logical sequence to assist the user• Default values should be set up whenever possible so a minimum of data

entry is required• Full help and exit facilities should be provided• WIMP Interface

Windows, Icons, Mouse and pull down menus.• Window – area on screen through which a particular piece of software or

data file may be viewed.• The window can be the whole screen or several windows can be set up, each

one being moved or resized, as necessary.• An icon is a small picture representing an item such as a piece of software.

Selected by using the mouse.• Mouse moves a cursor, positioning it were required and then selecting the

item.


6 – Perception, Attention, Memory and Learning

Learning Objectives

Explain how a potential user’s perception, attention, memory and learning can be taken into account when designing an interface.

A user interface needs to be designed with the typical perception traits in mind or else it will be confusing for them.

The colour and sound of the interface can also be important.

Red means a mistake has been made.

Green means everything is OK.

If the wrong colour is put with the wrong outcome (i.e. it shows green for something wrong) then it can seem confusing.

Also sounds can be used to illustrate errors, such as high pitched sounds for something good or low pitched, staccato sounds for something bad. It does not need to be too loud, but it does need to be correct.

Shapes can mean different things, for example starry shapes can indicate a headline or a big offer. Tick shapes can indicate correctness, crosses can indicate being incorrect.

Advertising and movement can be a good method to illustrate points, but it should be used only occasionally as well as with colours and pictures, so as not to distract the user.

When a user interface is being designed, only information relevant at that second should be displayed and no distraction should be caused.

Common ways to distract other people include using constant background sound tracks, bad colour combinations and inconsistent design. Animation, colours and pictures should only be used occasionally and the interface should be clear and easy to navigate through for everyone.

Thomas Roe13B/It1Mr. MoorePeople have short-term memory, i.e. not remembering a lot of things for a long period of time. Due to this, the user interface should have common features, such as a navigation bar, so that the user will be familiar with these and will be able to navigate through the site with ease, without having any unnecessary shocks along the way. The background, text and pictures should be consistent in order to ease this process.

A user interface should be mostly like typical interfaces. This means that the user will find it much easier to navigate through than if a really complicated interface was used and because of this, the learning curve would be much shallower for the user. There needs to be a lot of instructions present in order to guide the user through the interface if there are any problems that could crop up during design.


7 – Mental Models

Learning Objectives

Describe mental models and how they can be applied to the design of a user interface.

Discuss the importance of designing a system model that matches closely the user’s mental model.

Task One

Answer these questions about mental models:

1.) What is a mental model?

2.) What might go wrong with a system which did not match a user’s mental model? Use everyday examples such as traffic lights or screws (clockwise to screw in anti to unscrew etc or on/off switches) in your answer.

A mental model is a constant stream of information that is processed by the brain to help it achieve specific tasks. For example, when the brake pedal is pressed in a car, the car should stop.

A mental model is formed of the expected event so if the system did not match the personal mental model, accidents could happen. For example, if the brake pedal in the car was pressed and the car did not brake or it accelerated, the mental model will be perceived to be incorrect and the car will probably need to be taken to a mechanic to have it checked.

Task Two

1.) Using a pen and paper or using design software on the computer, design a user interface for a mobile phone or anything else similar that the user will find intuitive and easy to use.

2.) On your design annotate the features that conform to a user's mental model and their expectations about how things should work.

3.) What will the user expect from each of these features and why is having this in place important?

Thomas Roe13B/It1Mr. Moore4.) What kind of effect will following mental models have on the user's experience of the system? What would it be like if you didn't follow mental models?

Benefits of conforming to a mental model

Predictability Easy to learn Easy to use Simple to find controls

Problems with a non-conforming interface

Difficult to learn quickly Harder for guessing where things are Mistakes more likely to happen


8 – Model Human Processor Learning Objectives

- Describe the user interface design tool known as the Model Human Processor

- Explain how its principles can be applied in terms of computer based interactive systems.

The model begins with the fact that our ears and eyes are input sensors. Each of these inputs is provided as separate channels as they store different types of information.

This information can only be stored for a few seconds and it will disappear after a period of time as this is short term memory.

As this happens, this information has to be processed so as much of the information as possible is kept for a longer period of time without being forgotten again.

The outputs from the audio and visual sources are stored in a cognitive source (i.e. stored together). Multiple interface streams are being combined in one go, so this is why there should not be any confusion between the information (also known as “cognitive dissonance”). Only a limited amount of information can be stored at any one time, typically 7 elements. A good example of this would be a 7 digit telephone number.


However, the information will only be remembered for a short time unless the user is reminded of the action at a later stage in the processing.

This information is then fed into the cognitive processor. This information is combined with information stored in long-term memory to try to ascertain a complete understanding of the instantaneous occurrences. If the effort is worthwhile, then the new information is put into the long-term memory store.

If something needs to be released from long-term memory, then recognition is much faster than recall because there is nothing in recall that is easily recognisable. An instantaneous answer is much harder to find in recall than in recognition.

The last thing involved in the model human processor is the physical part where things have to be done. There is a muscle memory able to do these things without even thinking about doing them, they will become “second nature” to people.

Although the model human processor works well in some cases, it does present a few problems.

The processor assumes that the person concerned is doing one thing at a time.

The processor does not consider the effects of other people.

There is no consideration for the environmental conditions.


OCR A2 ICT – Theory, Chapter 2Mid Chapter Mini Quiz

1. Define batch processing.3 marks

2. Define interactive processing.3 marks

3. What is an operating system?2 marks

4. Give an e.g. of when a single user OS might be used.1 mark

5. What is a multi tasking OS? 3 marks

6. List the 6 factors that you must consider when designing a HCI.

6 marks

7. List the 4 main features of interaction between a computer and a person.

4 marks

8. What 2 types of prompts are most commonly used in a GUI?

2 marks

Thomas Roe13B/It1Mr. Moore9. How does a batch processing system differ to an

interactive OS?3 marks

10. Explain what you think a ‘natural language’ HCI might be.

3 marks


OCR A2 ICT – Theory, Chapter 2Mid Chapter Mini Quiz - Answers

11. Define batch processing.3 marks

Where large amounts of the same or similar data is processed in batches. Usually done in the evening’s or at weekends when the system is not being used. An example of this could be printing utility bills such as gas bills.

12. Define interactive processing.3 marks

Where data is processed one transaction at a time, often used in booking systems for e.g. booking tickets. This is so that seats can’t be sold more than once.

13. What is an operating system?2 marks

The ‘brain’ of the computer. It is the core software that allows the computer to be used as a useful device.

14. Give an e.g. of when a single user OS might be used.1 mark

On a personal computer or a smart phone.

15. What is a multi tasking OS?3 marks

An operating system that allows you to work within several different applications at the same time e.g. using both the Internet and word processing software at the same time.

16. List the 6 factors that you must consider when designing a HCI.

6 marksUse of colour, layout, quantity of information, font size, complexity of language and type of controls

17. List the 4 main features of interaction between a computer and a person.

4 marks

Prompts, nature of input, methods of input and feedback

18. What 2 types of prompts are most commonly used in a GUI?

2 marksMenus and icons

19. How does a batch OS differ to an interactive OS?

3 marksBatch OS is given a set of tasks to run without any user intervention whereas an interactive OS is one in which there is durect user interaction while a program is running

20. Explain what you think a ‘natural language’ HCI might be.

3 marksFor e.g. a satnav which allows the user to select by speaking into the device.


Networks & Communication1 – Bandwidth and Transmitting Data

Bandwidth is a measure of the capacity of a communications channel. It is measured in bits per second. It is common to use kilobits per second and megabits per second

Thomas Roe13B/It1Mr. Mooreto describe the bandwidth of modern links, such as the Internet. Bandwidth determines the overall connection speed of a network. The lowest bandwidth determines the maximum speed.

Early modems have a speed of 300-9600 bits per second.

Modern modems have a speed of 56 kilobits per second.

ISDN (Integrated Services Digital Networks) have a speed of 64-128 kilobits per second.

Most ADSL (Asymmetric Digital Subscriber Line) links have a speed of 512 kilobits per second to 2 megabits (2000 kilobits) per second.

High-end networks in Korea, Sweden and Japan have a connection speed from 2 megabits per second to 1000 megabits per second.

There are 3 different types of cable that can be used for connections.

Copper Cabling consists of a copper core surrounded by insulation.

UTP (Unshielded twisted pair) cabling is used to reduce signal loss. However, twisted pair cabling can be used to prevent interference between the signals.

Fibre optic cabling uses light to transmit information rather than electrical signals.

• LANs and Extranets• Thomas Roe• 13B/It1• Mr. Moore• LANs• Also known as Local Area Networks.


• Small area (e.g. schools, offices)• One computer is the file server, rest are workstations.• Cables are used to connect the computers together.• Advantages of Local Area Networks• Fast data transfer.• Low cost for set up.• Secure network.• All software loaded on 1 computer.• Share resources.• E-mail can be accessed.• Disadvantages of Local Area Networks• Expensive installation• Expertise for administration.• File server may fail, whole system halts.• Cable can break, whole network stops.• Extranets• Private networks - use technology from Internet and telecommunications

devices - share information with others.• Similar to an intranet - extended to an outside company.• Requires security and privacy. Firewalls and encryption techniques.• Uses of Extranets• Large amounts of data can be exchanged using EDI, many data segments

involving singular facts from many data elements can be transferred.• Catalogues exclusively shared.• Software programmes can be developed and used by the business.• Services for other companies can be accessed and used.• News of common interest between the employees can be shared.

Network Topologies

There are 3 types of network topology; bus, ring and star. They all have their advantages and disadvantages.

Thomas Roe13B/It1Mr. MooreA bus network consists of a single cable which connects all of the hardware and computers together.

It is the best choice for temporary networks, it is easy to install, it uses little cabling and it is simple to add extra workstations.

However, there is limited security, a maximum number of workstations, a termination in the connection if the central cable fails and data collisions for large amounts of data, which can travel slowly.

4 – Networks – Client & Peer to Peer

Quiz


Round 1 – Networks

1. Name 3 advantages of networks. [3]

2. Name 3 disadvantages of networks. [3]

Round 2 – Client Server

3. What is a client server network? [3]

4. Name 3 advantages of client server networks. [3]

5. Name 3 disadvantages of client server networks. [3]

Round 3 – Peer to Peer

6. What is a peer to peer network? [2]

7. Name 3 advantages of peer to peer networks. [3]

8. Name 3 disadvantages of peer to peer networks. [3]

Round 4 – True or False

Thomas Roe13B/It1Mr. Moore9. A peer-peer network is complex to set up. [1]

10. A client server only needs basic skills? [1]

11. A peer to peer has a server? [1]

12. A client server has all the applications loaded onto every computer? [1]

13. A client server uses a better operating system? [1]

14. A peer to peer has the lowest level of security? [1]

15. A peer to peer has basic login settings? [1]

16. Are devices managed centrally in a client server network? [1]

17. In which network can users roam from machine to machine? [1]

4 – Networks – Client & Peer to Peer

Answers

Thomas Roe13B/It1Mr. Moore18. Name 3 advantages of networks.

3 from:

Accessibility of data, internet connection, software, files. Share Hardware/Software Security Issues Central Backup

19. Name 3 disadvantages of networks.

3 from:

Network Failure Data Transfer/slowing down network Viruses Expensive equipment Expert Support

20. What is a client server network?

A client-server network is a network where clients are connected to a central hub, which is then connected to a central server on the system. If the server goes down, the client’s connection goes down.

21. Name 3 advantages of client server networks.

3 from: All files are stored in a central location Network peripherals are controlled centrally Backups and network security are controlled centrally Users can access shared data which is centrally controlled.

22. Name 3 disadvantages of client server networks.

3 from: A specialist operating system is needed

Thomas Roe13B/It1Mr. Moore The server is expensive to purchase Specialist staff such as a network manager is needed If any part of the network fails, a lot of disruption can occur.

23. What is a peer to peer network?

A peer to peer network is one where no central server is needed to access the network. This is as simple as two people using a hub to connect to each other’s computer. However, the permission rights do have to be set so no-one can see each other’s work. For example Peer 1 cannot see Peer 2’s work unless Peer 2 gives Peer 1 permission to do so.

24. Name 3 advantages of peer to peer networks.

3 from: There is no need for a network operating system It does not need an expensive server There is no need for network technicians It does not need specialist knowledge to set up If one computer fails, no other computers are affected (it just means no-one can

access their work).

25. Name 3 disadvantages of peer to peer networks.

3 from: The performance may be slowed because each computer is accessed Files and folders cannot be centrally backed up Files and resources are not centrally organised Individual users need to ensure viruses are controlled There is little security beside the permissions.

26. A peer-peer network is complex to set up.FALSE

27. A client server only needs basic skills.FALSE


28. A peer to peer has a server.FALSE

29. A client server has all the applications loaded onto every computer.FALSE

30. A client server uses a better operating system.TRUE

31. A peer to peer has the lowest level of security.TRUE

32. A peer-peer has basic login settings.TRUE

33. Are devices managed centrally in a client-server network?YES

34. In which network can users roam from machine to machine?CLIENT-SERVER

Optical Communication MethodsLearning Objectives Understand the different optical communication methods.Discuss their advantages and disadvantages.Discuss typical applications of optical communication.Infra-red is the earliest type of communication and is in use today. Their uses are in TV, DVD and entertainment remotes. The speed of this communication is about 115.2

Thomas Roe13B/It1Mr. Moorekbps. It has a range of 10 metres. It is cheap, it has a moderate bandwidth and it does well on short distances. However, it can only be used in line of sight, it has a short range and it has a low bandwidth compared to other communication types.Fibre Optic communication has the widest bandwidth and is made from glass fibre. A transmitter converts the input into light and a detector converts the light into output. A repeater is needed every 70 kilometres. Data is transferred at 40 GB per second. 1% of fibre optics is lit for paying customers. Fibre optic is immune to interference. Signals can be sent over a longer distance, it has a large data capacity, it is immune to electric interference and corrosion, many services can be on the same line, it is used in hazardous environments, the security is good, one cable is used for many fibres and each fibre is used for a different service. However, fibre optic is expensive, the connection is difficult, expertise is required, it cannot carry power and failure of this is worse than copper.Laser communication can also be used for communication between campuses, emergency data links, back-up networks and outdoor events. It has a wide bandwidth compared to infra-red and is quick to set up. However, it is affected by the weather and needs line-of-sight to be able to work. LASER stands for Light Amplification by Stimulated Emission of Radiation.

7 – Communication Applications

E-mail

/w EPDw UJNDU1O


Sort by

Electronic mail is a method of exchanging digital messages across the Internet or other computer networks.Electronic mail, commonly called e-mail, is a method of exchanging digital messages across the Internet or other computer networks.You can attach files to accompany your messagee.g. pictures, links, or files.These attachments can also be viruses however.

Uses

BusinessFriends & FamilyBroadcast infosending & receiving documents

Confidentiality important

Pros & Cons

Little trainingFree to sendQuick responseNot presentAny timeAttachmentsMultiple copiesCarbon copyRequest proofPrepared in advanceEncryptionElectronic signatures

Must have e-mail addressNo message if no e-mail address knownChange e-mail addressSPAMWastes working timeInboxes can be full (for example, when going on holiday) Waiting a long time for messagesVIRUSESSome companies don't allow attachmentsEMAIL SCAMSNo guarantee from legitimate sender. E-mails can be SPOOFED.

Thomas ROE wrote:

BusinessFriends & FamilyBroadcast infosending & receiving documents

Date


Confidentiality important

I should clarify that Thomas means that this can be used in between business employees and other businesses and between everyone and anyone else on the planet.

It’s also used to make sales and to send people viruses.

The original email systems allowed communication only between users who logged into the same host or "mainframe". This could be hundreds or even thousands of users within an organization.


Tele/Video Conferencing

Sort by

A videoconference is a set of interactive telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously.

Audio & Video Conferencing

This allows people in different locations to communicate with each other.

Uses: Business meetings, training, education, family and friends (webcam is cheap), gaming, virtual tourism, remote medical care.

Pros: No need for time and money travelling, seeing people as well as hearing them, no need for others to travel to one location, everyone views something, ideas and knowledge communicated between people, one trainer can provide lectures to hundreds of people at the same time.

Cons: Access to hardware and software required, fast data link needed, slight delay between responses (even with a fast connection), hardware breakdown means everyone suffers, different time zones, no substitute for face to face meeting.

Issue: Eye contact plays a large role in conversational turn-taking, perceived attention and intent, and other aspects of group communication. Some systems have cameras located in the screens that reduce this. The issue of eye-contact may be solved with advancing technology.

Can't you still see people's eyes when you are on camera??

The point here is if you look at your webcam on your laptop, it is not where you will be looking on the screen aka you will not be looking directly into the camera which means that you will not be making 'eye contact' which in some cultures is perceived as being rude. (Issues with using video conferencing internationally here!)

You will be losing out on body language that is important in the business world especially when trying to convince somebody or sell something to them. This would be a disadvantage of video conferencing as the application would not be suitable to this situation.

Alan sugar makes the most of it on apprentice

video conferencing is used in law where individuals cannot attend the physical legal setting

It may also be used for witness protection where the witness is too distressed or scared to be in the same room/building as the accused.

Can also be used in the court rooms where the defendant is too young to stand and give evidence.

With high speed internet video conferencing has become easier and more available

Date

/w EWBQKp96Hx


Bulletin Boards

Sort by

A bulletin board is a place where people can leave public messages, for example, to advertise things to buy or sell, announce events, or provide information.Message boards and even internet forums are interchangeable

Bulletin boards are particularly prevalent at universities. There are hundreds of thousands of public bulletin boards, used for everything from advertisements by extracurricular groups and local shops to official notices.

Internet forums are becoming a global replacement for traditional bulletins. Online bulletin boards are sometimes referred to as message boards. The terms bulletin board, message boards and even internet forums are interchangeable, although often one bulletin board or message board can contain a number of internet forums or discussion groups. An online board can serve the same purpose as a physical bulletin board.

Bulletin Boards

Internet based

Often called a "forum"

This is a bulletin board.

Forums set up for everything, can be used by anyone (informal or formal)

Un-moderated (posts loaded as soon as they are sent) or moderated (someone looks at it before it is sent), this is an un-moderated one.

Excellent knowledge base.

Terms: "Forum" or "Board" ( topic area), "Thread" (related messages), "Post" (single message), "Troll" (deliberate offender), "Lurker" (reads messages, not replying)

Uses: Hobbies, sharing knowledge, discussing real-time events, professional

I may be a "lurker" as I have only sent one message in each category.

Is this an un-moderated board Thomas? ;)

WHAT IS UNMODERATED?

This is a moderated board

Moderated means that the forum has someone checking over the board for offensive posts and is checking what people write. Thomas said that this forum was un-moderated which I disagree with.

If you post anything offensive, is it likely to be on here in 5 minutes time?

Date

Thomas Roe13B/It1Mr. MooreInternet forums are becoming a global replacement for traditional bulletins. They are also used for business purposes, where individuals/creators make money through advertising. So, can be a source of finance.

Fax

Sort by

A fax (short for facsimile) is a document sent over a telephone line :)Fax machines are normally used in a business environment rather than personal use, as it can send a lot of information at once. Personal users don't use them as there are quicker ways of communicating such as e-mail.The main alternatives are e-mail and Internet fax. Internet fax uses the Internet to receive and send faxes.Fax is also paper based and used for sending documents, scanning the paper document at one end and printing it out at the other. For email you would need to scan the document to send as an attachment

FAX

Transmits image copy of graphical info

only deals with A4

Optical scanner able to do this

Converts into digital file

Used in business offices for:

InvoicesOrdersDrawings/SketchesContracts

There are A3 fax machines!!!

I've seen an A3 FAX machine.

Date


Internet Relay Chat

Sort by

Richard Moore Internet Relay Chat

Research Internet Relay Chat and store the information here. There are some useful links under 7. Communication Applications

David CLARKEIRC is an internet protocol.

Date


Thomas ROE IRC What is it?

Text based real time messaging system; uses are chatting to friends using text, webcam services and business colleague messages.

Features

View messages"Buddy" listsBlock peopleUse graphical imagesStatus availableSending attachmentsArchive messagesInviting people for a chat

Joshua COOPERIRC is mainly designed for group communication in things called

'channels'


Josh WEATHERBYBecause IRC connections are usually unencrypted and typically

span long time periods, they are an attractive target for crackers. Because of this, careful security policy is necessary to ensure that an IRC network is not susceptible to an attack such as an IRC takeover war. IRC networks may also K-line or G-line users or networks that have a harming effect.

Matthew SCHOFIELDAn IRC Server can connect to several other IRC Servers which

expands the network.

Joshua COOPERIRC is easily archived.

IRC is accessed through programs called 'clients'

a popular example of a client would be mIRC or XChat


Francesca SPARHAM IRC QUIT You can end a session by entering the command: "QUIT"

Parameters: []

David CLARKEA user may be part of several channels at once.

However, the use of 10 channels is recommended as a limit for all standards of users.

Jodi LEWIS K line and G line When a user is k-lined, it bans the user from a certain server, either

for a certain amount of time or permanently.

G-line or global kill line (also written G:line) is a global network ban applied to a user


Joshua COOPERIRC uses 'bots' to help protect channels and act as points of contact

for information and protection. Bots are always being developed for more complex tasks - such as a 'trivia' bot which starts up a trivia game.

Josh WEATHERBYK-Line - Internet Relay Chat term, applied to a specific user. When a

user is k-lined, it bans the user from a certain server, either for a certain amount of time or permanently. Once the user is banned, they are not allowed back onto that server; they have to join a different server to get onto IRC.

G-Line - is a global network ban applied to a user. Whenever a G-lined person attempts to connect to the IRC network, the services will automatically disconnect the client

Martin WILCOXUsers can create file servers that allow them to share files with each

other by using customised IRC bots or scripts for their IRC client


Jodi LEWIS A lot of use... As of May 2009, the top 100 IRC networks served more than half a

million users at a time, with hundreds of thousands of channels

Joshua COOPERIRC Bouncers are 'ghost' users or a persistent proxy. The main

purpose is to maintain a connection to an IRC server - if the client loses connection to a certain IRC server - the bouncer will remain connected and archive the chat. This will allow the user to reconnect and resume his IRC session.

David CLARKEFirst programmes created for the initial time-sharing computers in

early 1960's were designed to be able to support real-time chat


Joshua COOPER'Quakenet' www.quakenet.org - is the largest IRC network in the

world.posted 26/11/2010 09:04

Josh WEATHERBYMost modern servers support detection of users attempting to

connect through an insecure (exploited) proxy server, which can then be denied a connection.

Francesca SPARHAM Host masks A host mask is a unique identifier of an IRC client connected to an

IRC server. IRC services and bots can use it to identify the client. The host mask looks similar to, but should not be confused with, an e-mail address. It is a combination of the nickname, identity, and hostname. If identity is not available, then the username is used after being prefixed with a tilde sign. If the IP address cannot be resolved to a valid hostname, then the IP address is used instead.


Jodi LEWIS Modes Users and channels may have modes which are represented by

single case-sensitive letters and are set using the mode command.User modes and channel modes are separate and can use the same letter to mean different things

e.g. LetterI DescriptionInvisible? Cannot be seen without a common channel or knowing the exact name

Matthew SCHOFIELDAutomated clients are called bots.

Most modern IRC services typically implement bot-like interfaces, through which users can communicate with and control the functionality. Bots have also been created for malevolent uses, such as flooding or taking over channels, ousting their rightful owners.

Jodi LEWIS PROBLEMS


Issues in the original design of IRC were the amount of shared state data being a limitation on its scalability, the absence of unique user identifications leading to the nickname collision problem....

Matthew SCHOFIELDFlooding or scrolling on an IRC network is a method of disconnecting

users from an IRC server. It will exhaust bandwidth, thereby causing network latency ('lag'), or just annoying users. Floods can either be done by scripts (written for a given client) or by external programs. It is possible to flood a user off simply by sending those data faster than they can receive it.


8 – Comparing Broadband Connections

In order to consolidate what we have learnt so far, look back over sections 3-6 and create a table that looks like this:

Example Situation

Connection Type Suggested

Justification

Homes ADSL

This would be most appropriate so the users can get a quick connection with minimal cable usage.

Small businesses Wireless

This would be most appropriate as shopping centres would not want cables as it would present a tripping hazard for other people inside the small business.

Schools Wireless

This would be most appropriate as schools would not want cables as it would present a tripping hazard to other students.

Banks Leased Line

This would be most appropriate as banks would not want cables as it would present a tripping hazard.

Global Positioning Systems in cars Satellite

This would be most appropriate as they are situated in the sky so it would be easy to track the position of the vehicle.

Shopping centres Wireless This would be most appropriate as shopping centres want people to be able to connect quickly


without having the hassle of cables.

Abroad on holiday Wireless

When people are abroad, they want fast connections to be able to keep up with news back at home.

Asymmetric Digital Subscriber Line (ADSL, generic broadband connection)

Cable

Wireless

Leased Line

Satellite

System

The Switching system (SS) is very operative system in which many crucial operations are conducted, SS holds five databases with in it which performs different functions. If we talk about major tasks of SS system it performs call processing and subscriber related functions. These five databases from SS systems are HLR, MSC, VLR, AUC and EIR. Let’s study each database in detail and learn what functions this little systems performs.

Thomas Roe13B/It1Mr. MooreHLR- Home Location Register:HLR is database, which holds very important information of subscribers. It is mostly known for storing and managing information of subscribers. It contains subscriber service profile, status of activities, information about locations and permanent data of all sorts. When new connections are purchased, these subscribers are registered in HLR of mobile phone companies.

MSC- Mobile Services Switching Centre:

MSC is also important part of SS, it handles technical end of telephony. It is built to perform switching functionality of the entire system. It’s most important task is to control the calls to and from other telephones, which means it controls calls from same networks and calls from other networks. Toll ticketing, common channel signalling, network interfacing etc. are other tasks which MSC is responsible for.

VLR- Visitor Location Register:

VLR performs very dynamic tasks; it is database which stores temporary data regarding subscribers which is needed by Mobile Services Switching Centre-MSC VLR is directly connected to MSC, when subscribe moves to different MSC location, Visitor location register – VLR integrates to MSC of current location and requests the data about subscriber or Mobile station (MS) from the Home Location Register –HLR. When subscriber makes a call the Visitor location register-VLR will have required information for making call already and it will not be required to connect to Home Register Location - HRL again.

AUC- Authentication Centres:

AUC is small unit which handles the security end of the system. Its major task is to authenticate and encrypt those parameters which verify user’s identification and hence enables the confidentiality of each call made by subscriber. Authentication centre – AUC makes sure mobile operators are safe from different frauds most likely to happen when hackers are looking for even smallest loop wholes in systems.

EIR – Equipment Identity Register:

EIR is another important database which holds crucial information regarding mobile equipments. EIR helps in restricting for calls been stolen, mal functioning of any MS, or unauthorized access. AUC – Authentication centre and EIR- Equipment Identity registers are either Stand-alone nodes or sometimes work together as combined AUC/EIR nodes for optimum performance.

The Base Station System (BSS)

The base station system have very important role in mobile communication. BSS are basically out door units which consist of iron rods and are usually of high length. BSS are responsible for connecting subscribers (MS) to mobile networks. All the communication is made in Radio transmission. The Base station System is further divided in two systems. These two systems, they are BSC, and BTS. Let’s study these two systems in detail.

BTS – The Base Transceiver Station:

Thomas Roe13B/It1Mr. MooreSubscriber, MS (Mobile Station) or mobile phone connects to mobile network through BTS; it handles communication using radio transmission with mobile station. As name suggests, Base transceiver Station is the radio equipment which receive and transmit voice data at the same time. BSC control group of BTSs.

BSC – The Base Station Controller:

The Base Station normally controls many cells, it registers subscribers, responsible for MS handovers etc. It creates physical link between subscriber (MS) and BTS, then manage and controls functions of it. It performs the function of high quality switch by handover over the MS to next BSC when MS goes out of the current range of BTS, it helps in connecting to next in range BTS to keep the connection alive within the network. It also performs functions like cell configuration data, control radio frequency in BTS. Data moves to MSC-Mobile switching centre after BSC done processing it. MSC is switching centre which acts as bridge between different mobile networks.

Making a Phone Call via Satellite

1. A subscriber in Russia is calling her friend in San Francisco on her satellite phone. Her signal is handled by a passing satellite.

2. The satellite relays the call to a Gateway in its footprint.

3. The Gateway converts the signal to work with the local public service telephone network (PSTN) and passes on the call. Depending on the distance between the callers, a satellite call might pass through several Gateways and PSTNs

Thomas Roe13B/It1Mr. Moorebefore locating the receiving phone. The PSTN uses the call's routing information to connect to another Gateway that knows where the receiving phone is located.

4. The Gateway located closest to the receiving phone converts the signal to the correct format and uplinks it to a satellite (5). This Gateway knows that the receiving phone is in its contact area because an earlier satellite relayed that phone's power-on registration message to the Gateway. This information was stored in the Gateway's Visitor Location Register (VLR).

6. The call is relayed to the receiving phone and the call linkage is complete!

SATELLITE Television

Television could not exist in its contemporary form without satellites. Since 10 July 1962, when NASA technicians in Maine transmitted fuzzy images of themselves to engineers at a receiving station in England using the Telstar satellite, orbiting communications satellites have been routinely used to deliver television news and programming between companies and to broadcasters and cable operators. And since the mid-1980s they have been increasingly used to broadcast programming directly to viewers, to distribute advertising, and to provide live news coverage.

Arthur C. Clarke, a British engineer turned author, is credited with envisioning the key elements of satellite communications long before the technical skill or political will to implement his ideas existed. In 1945 he published a plan to put electronic relay stations--a radio receiver and re-transmitter--into space at 23,000 miles above the earth's equator. At this altitude, the satellite must complete a full rotation around the earth every 24 hours in order to sustain orbit (countering the pull of the earth's gravity). Given the rotation of the earth itself, that keeps the satellite at the same relative position. This "geosynchronous orbit" is where several hundred communications satellites sit today providing telephone and data communications, but mostly, relaying television signals. Television is currently the largest user of satellite bandwidth.

An "uplink" transmitter on earth, using a "dish" antenna pointed toward the satellite, sends a signal to one of the satellite's "transponders." The transponder amplifies that signal and shifts it to another frequency (so as not to interfere with the incoming signal) to be transmitted back to earth. A "downlink" antenna and receiver on earth then captures that signal and sends it on its way. The essential advantage of the satellite is that the uplink and downlink may be 8000 miles apart. In practice, satellite communications is more efficient over a shorter distances than that, but the advantages over terrestrial transmissions--cable, fiber optics, and microwave--are profound, particularly across oceans. As with Direct Broadcast Satellites (DBS), satellites can transmit to an unlimited number of ground receivers simultaneously, and costs do not increase with distance.

Each satellite has a distinct "footprint," or coverage area, which is meticulously shaped and plotted. In 1971, the first communications satellites carrying "spot beam" antennas were launched. A spot beam antenna can be steered to focus the satellite's reception and transmission capabilities on a small portion of the earth, instead of the 40% of the earth's

Thomas Roe13B/It1Mr. Mooresurface a wider antenna beam could cover. Spot coverage is crucial in international broadcasting, when neighboring countries may object to signal "spillover" into their territory.

Communications satellites since the 1960's have received uplink signals in a range of frequencies (or "bandwidth") near six GHz (gigahertz, or a billion cycles per second) and downlinked signals near four GHz. This range of frequencies is known as "C-band." Each range of frequencies is subdivided into specific channels, which, in the case of C-band, are each from 36 to 72 MHz wide. A single analog television transmission may occupy enough bandwidth to fully utilize a single 36 Mhz channel. Hundreds or thousands of voice or data signals requiring far less bandwidth would fit on the same channel. In the 1980s a new generation of satellites using bandwidths of 11 to 12 GHz (uplink) and 14 GHz (downlink) came into use. The "Ku-band" does not require as much power to be transmitted clearly, thereby permitting the use of small (and less expensive) earth stations for uplink and downlink. With the introduction of the Ku-band, television entered the era of live news--satellite news gathering (SNG)--as "Ku-band" satellites made it easy to uplink television signals with a portable dish from the scene of a breaking news story. Television news has also made some use of another satellite technology, remote sensing, using pictures taken by satellites to illustrate or verify news stories.

In the late 1970s, with the satellite distribution of Home Box Office, home satellite dishes, or "television receive only" (TVRO), became popular for people out of reach of cable television. Later, direct satellite broadcasting (DBS) to small home dishes became possible through the use of these higher frequencies. Since 1988 DBS has been heavily used in Europe, and it is rapidly gaining popularity in the United States. Overuse of the C and Ku bandwidths and the desire for even greater signal strength is leading to new satellites that use other areas of the radio spectrum. A typical communications satellite launched in the early 1990s has a mix of C and Ku-band transponders, and is capable of relaying over 30,000 voice or data circuits and four or more television transmissions. Telephony and television use roughly equivalent portions of available satellite capacity, but the demand for DBS has led to a number of satellites dedicated to TV transmission.

Like other communications technologies, the satellite industry has embraced digitalization and signal compression as a means of maximizing the use of limited bandwidth. By converting analog signals to digital signals, less bandwidth is required, and digital signals can be broken into smaller pieces for transmission through bits of available bandwidth, and reassembled at the point of reception. Compression eliminates otherwise redundant portions of a television transmission, allowing for a signal to be sent using far less bandwidth. Encryption, or scrambling, of satellite television signals is now becoming common to ensure that only customers who have bought or rented a decoder can receive transmissions. Even inter-company television feeds via satellite, such as daily feeds to broadcasters from television news agencies, are being encrypted to prevent unauthorized use. Typical television transmissions via satellite in the 1990s are digital, and are often compressed and encrypted. Compression technology is expected to considerably increase the number of DBS services available.

Some developing countries have demonstrated success in using satellite delivered television to provide useful information to portions of their populations out of reach of terrestrial broadcasting. In 1975, an experimental satellite communications project called SITE (Satellite Instructional Television Experiment) was used to bring informational television programs to rural India. The project led to Indian development of its own satellite network. China has also embarked on a ambitious program of satellite use for development, claiming substantial success in rural education.

STAR-TV, controlled by media mogul Rupert Murdoch, transmits television programming over much of Asia and has forced governments worldwide to reevaluate their stance on issues of national sovereignty and control of incoming information. STAR-TV reaches over 50 countries and potentially half of the world's population--far more than any other satellite television service (though it is technically not DBS, still requiring larger dishes). A slew of contentious political and cultural issues have resulted. Murdoch dropped BBC World Service Television

Thomas Roe13B/It1Mr. Moorefrom his STAR-TV program lineup as a concession to the Chinese government. Other governments have complained about the unrestricted importation of news presented from an Anglo-American viewpoint, though their concerns about political consequences are often couched in terms of protecting local culture. Reports of disruptions to local cultures stemming from international satellite broadcasting are widespread.

In all these instances satellite technology has called into question conventional notions of the nation state. Geographic borders may be insufficient definitions of culture and nationality in an era of electronic information, beamed from multiple sources into the sky, and down again into almost any location.

-Chris Paterson

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