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Fundamental Chapter 4

Q. Describe the various application of Networking?

Ans:-  There is a long list of application areas which can be benefited by establishing networks few of the applications of computer networks are:-

·   Information retrieval systems which search for books, technical reports, papers and articles on particular topics.
·   News access machines which can search past news, stories or abstracts with given search criteria.
·        Airline reservation, hotel-booking, railway reservation, car rental etc.
·  A writer’s aid; A dictionary, thesaurus, phrase generator, indexed dictionary of quotations etc.
·    Stock market information systems which allow searches for stocks that meet certain criteria, performance comparisons, moving averages, and various forecasting techniques.
·        Electronic financial transactions (FFT) between banks and via cheque clearing house.
·        Electronic mail messages systems (EMMS).
·  Corporate information systems such as marketing information system, customer information system, product information system, personnel information system etc.
·  Corporate systems of different systems such as order-entry system, centralized purchasing, distributed inventory control etc.
·        On-line systems for investment advice and management, tax minimization etc.
·        Resources of interest to a home user.
·        Sports results.
·        Theater, movies and community events information.
·        Shopping information, prices, advertisements.
·        Restaurants, good food guide.
·        Household magazine, book reviews, film reviews etc.
·        Holidays, hotels, travel booking.
·        Radio & TV programs.
·        Medical assistance service.
·        Insurance information
·        Transmission channel
·        Network Interface Unit (NIU)
·        Servers
·        Workstations

Q.  Write a Short note on the following.

i. Analog and Digital Signal
ii. Bandwidth
Analog and Digital Signals:-  Like the data they represent, signals can be either analog or digital.  An analog signal has infinitely many levels of intensity over a period of time.  As the waves moves from value A to value B.  It passes through and includes an Infinite number of values along its path.  A digital signal, on the other hand, can have only a limited number of defined values.  Although each value can be any number, it is often as simple as 1 and 0.

Program:-  Comparison of Analog and Digital signals.

Bandwidth:-  Difference between the maximum and minimum frequency of a frequency spectrum of the signal is known as bandwidth of the signal.
Here the term frequency spectrum of a signal means the set of all frequencies that constitutes it.  A simple signal has only a single frequency, However a complex signal can be broken down into simple signals having different frequencies.  The set of these frequencies are known as spectrum of the signal.
In other words, we can say that the difference between the highest frequency and the lowest frequency is known as bandwidth.  To calculate the bandwidth, Subtract the lowest frequency from the highest frequency of the range.

Frequency:-  The frequency is the rate at which the signal repeats.

Q.  Write a short note on the following.
i. Packet Transmission
ii. Long Distance Communication

Ans:- Packet Transmission:-  In a packet transmission, data are transmitted in discrete units of potentially variable.  Variable length blocks called packet is established by the network.  Longer transmission are broken up into multiple packets each packets contains not only data but also a header with control information (such as priority codes and source and destination addresses).  The packets are sent over node to node.
Two popular approaches of packet switching:-
·        Datagram approach
·        Virtual circuit approach

Datagram Approach:-  In Datagram approach, To packet transmission, each packet is treated independently from all others.  Even when one packet represents just a piece of multi packet transmission, the network treats it as though it existed alone.  Packets in this technology are referred to as datagrams.

This approach can cause the datagrams of a transmission of a transmission to arrive at their destination out of order.

Virtual Circuit Approach:-  In the virtual circuit approach to packet transmission, the relationship between all the packets belonging to a message.  A single route is chooses between sender and receiver at the beginning of the session.  When the data are sent, all the packets of the transmission one after another along that route.
Virtual circuit transmission is implemented in two formats:-
·        SVC (Switch Virtual Circuit)
·        PVC (Permanent Virtual Circuit)

SVC:-  In this method, a virtual circuit is created whenever it is needed.  For example- Imagine that station A wants to send four packets to station X.  First, A requests the establishment of a connection to X.  Once the connection is in place, the packets are sent one after another and is sequential order.  Only one single rate exists for the duration of transmission.
Each time that A wishes to communicate with X, a new route is established.  The route, many be the same each time or it may differ in response to varying network conditions.

PVC (Permanent Virtual Circuit):-  Permanent Virtual Circuits are comparable to leased lines in circuit switching.  In this method the same virtual circuit is provided between two users on a continuous basis.  The circuit is dedicated to the specific users.  No one else can use it and, because it is always in place.  It can be used without connection establishment and connection termination. Where as two SVC users may get a different route every time they request a connection, Two PVC users always get the same route.

Q. Explain the concepts of database with its relevant advantages and disadvantages. What are the characteristics  of an ideal database?


Database:-  A database is a collection of related information stored so that it is available to many uses for different purposes.  The content of a database is obtained by combining data from all the different sources in an organization.  Database play a critical role in almost all areas where computers are used, including business, law, engineering, medicine, education, library science etc.

The management of data in database system is done by means of a general purpose S/W package called a database management system.  The database management system is the major S/W component of a database system.  Some commercially available DBMS are INGRES, ORACLE, SYBASE.

The role of the DBMS as an intermediate between the users and the database is very much like the function of a salesperson in a consumers distributor system.  A consumer specified desired items by filling out an order from which is submitted to a salesperson at the counter.  The salesperson present the specified items to consumer after they have been retrieved from the storage room.  Similarly, the database use needs to know only what data he or she requires; the DBMS will take care of retrieving it.

Data:-  Data can be defined as a representation of facts, concepts or instruction in a formalized manner suitable for communication or processing by human or electronic machine.  Data is represented with the help of characters like Alphabets (a-z), digits (0-9) or special characters (1, -, 1, *, <, >, = etc.)

Data Item:-  A set of character which are used together to represent a specific data element.  Example Name of a student in a class is represented by the data item, say NAME.

Record:-  Record is a collection of related data items e.g- A payroll record for an employee contains such data fields as name, age, qualification, sex, basic pay, DA, HRA, PF etc.

File:-  File is a collection of related records stored in secondary storage that is available for future use e.g- Payroll file might consist of the employee pay records for a company.

Information:-  Information is classified data so that it has some meaningful values.

Data Processing:-  Data Processing means manipulating the data (raw data) to make it more useful.  Data Manipulation consists of such operation as classification, sorting & calculations etc.

Definition of Database:-  A database is well organized collection of data that are related in a meaningful way which can be accessed in different logical orders but are stored only once.
In this definition, it is clear that data in a database has the following features:-
·        It is well organized.
·        It is related.
·        It is accessible in different orders.
·        It is stored only once.

Data Base System, Concept and Meaning:-
A database system consists of a collection of interrelated data and a set of programs to access the data.  Hence, database system is the DBMS S/W together with the data itself.  It is a S/W that assists in maintaining and utilizing a database.
A Database Management System (DBMS) consists of –
·        A collection of interrelated data.  This part of DBMS is usually referred to as the database.
·        A set of application programs used to access, update and manage that data.  This portion forms the Data Management System.

The goal or purpose of a database system is to provide an environment that is both convenient and efficient to use in.
·        Retrieving information from the database, and
·        Storing information into the database.
In other words, a DBMS allows you to store, update and retrieve data hence making it easy to maintain and retrieve information from a database.

Advantages of Database System:-

·        Minimal Redundancy:-  In file systems each application has its own private files.  This can often lead to considerable redundancy in stored data, with reinltant waste in storage space.  For example, A personnel application and an education-records application may each own a file containing department information for employees.  These two files can be integrated, and the redundancy eliminated, if the DBA is aware of the data requirements for both applications.
·        Sharing of Data:-  It means not only that existing applications can share the data in the database, but also that new applications can be developed to operate against that same stored data.  In other words, the data requirements of new applications may be satisfied without having to create any new stored files.
·        Standards can be enforced:-  With central control of the database, the DBA can ensure that all applicable standards are followed in the representation of the data such as format of data items, documentation standards etc.  Which will result in uniformity of the entire database as well as its usage.
·        Search Capability:-  The user of a database may ask wide variety of the questions about the data if a quick answer is needed at a terminal the search will have to be fast the capability to search a database quickly.  An objective of database organization, then, may be achieve fast flexible search capability.
·        Integrity:-  By integrity we mean unification of several files into one file.  When a database contains data employed by many different users it is important that the data items & associations between data items not be destroyed.  Hardware failures  various types of accidents will occur occasionally.  The storage of data  its updating & insertion procedures, must be such that the system can recover from these circumstances without harm to the data.  This integration eliminates inconsistency.
·        Privacy & Security:-  Data in database systems must be kept secure & private.  Data security refers to protection of data against accidental or intentional disclosure to unauthorized persons or unauthorized modifications.
·        The Interface with the past:-  Organizations which have been using data processing for some time having a major investment in their existing programs, procedures and data.  When an organization installs new data-base S/W it is important that it can work with the existing programs & procedures and that the existing data can be converted.
·        Data Migration:-  Some data are referenced very frequently and others only occasionally.  It is desirable to store the frequently reference data in such a manner that they can be accessed quickly  conveniently.  The rarely accessed data can be stored in a cheaper fashion.  The rarely accessed data can be stored on magnetic tape & frequently accessed data may be on disk or drum.
            The process of adjusting the storage of data is called data migration.

·        Faster development of new application:-  When a new application is proposed, it is likely that the data required is already stored in the database.  Therefore, development time is reduced as no file creation phase is required for the new application.
·        More control over concurrency:-  In a file system, if two users permitted to access the data simultaneously or both attempt to perform updates, they will interfere, with each other and one might overwrite the value recorded by the other.  A DBMS has subsystems to control concurrency so that transaction are not lost or performed incorrectly.

Disadvantages of Database System:-

·        High Cost of DBMS:-  Because a complete DBMS is very large and sophisticated piece of S/W, it is expensive to purchase.
·        High Hardware Cost:-  Additional memory and processing power may be required to run the DBMS, resulting in the need to upgrade the H/W.
·        High Programming Cost:-  Because a DBMS is a complex tool with many features, it requires experienced programmers resulting in extra payment for their heir and expertise.
·        Complex:-  Another major disadvantages is that database processing tends to complex, large amounts of data in many different formats can be interrelated in the database.
·        Backup & Recovery are more difficult:-  Determining the exact state of the database at the time of failure may be a problem.  It may be even more difficult to determine what should be done next.
            Even the failure of just one application program may pose serious problems.
·        Confidentiality, Privacy and Security:-  When information is centralized and is made available to users from remote locations, the possibilities of abuse are often more that in conventional data processing system.

Characteristics of an Ideal Database:-  A database represent some aspect of the real world, sometimes called the mini world or the Universe of Discourse (U.D.). In, general, an ideal database should provide the following facilities:-
a.      Creation of a file, addition to data, deletion of data, creation, addition and deletion of entire file.
b.      Retrieving data collectively or selectively.
c.      Sorting and indexing of data.
d.      Reports generation facilities.
e.      Mathematical functions can be performed on the data to fetch the desired calculation.

f.       To maintain the data integrity.

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