computer networking.

 

 INTRODUCTION TO COMPUTER NETWORKS

 

 

DATA COMMUNICATION  :-

when we communicate , we are  sharing  information . The sharing can be local or remote . between individuals, local communication usally oocurs face to face, while remote communication takes place over distance.

components :- 

A data  communication system has five components.

1. message :-

The message is the information (data) to be communicated . popular forms of information include text , number , pictures , audio and video. 

2. Sender :-  

Its a device which sends the data message. It can be a computer ,workstation , telephone handset , video camera and so on.

3. Receiver :-

Its a device that receives the message .

4. Transmission medium :- 

The transmission medium is the physical path by which a message travels fro sender to  receiver . Some examples of transmission media include twisted pair wire , coaxial cable , fibre-optic cable an d radio waves.

5. Protocol:- 

A protcol is a set of rules that govern data communications. It represents an agreement between  the comunicating devices . Without a protocol , two devices may be connected but not communicating just as a person speaking french cannot be understood by a person who speaks only japanese.

 Data representation :-

    Information can be in the form of text , numbers , images, audio, and video.

1. Text:- 

 Text symbols are represented with a sequence of bits 0 and 1. Each sequence is called a code and the process is called coding.Two coding standards are 

• Unicode

• ASCII

• Unicode:- 

unicode is an international coding standard where each letter , digit or symbol is represented with the unique sequence of 32 0s and 1s . so this code can define 232 characters . It can be used in different languages.

Notation :  U-XXXXXXXX

Where X= hexadecimal number and ranges from 0 to F.

• ASCII  :-

American standard code for information interchange is a coding standard where each letter, number or symobls represented with  unique sequence of 7 0s and 1s . so  this code can define 27 (128)  character . It is    used for english language only .

ASCII ( Basic Latin ) is subset of unicode and occupies first 7 bits of unicode for 128 code and is represented in hexadecimal form as :

00000000-0000007F

     2 . Number :-

Number are also represented with a sequence of 0 and 1. ASCII is not used for number representation . Instead , the   following numbering system is used in order to simplify  the mathematical operations :

• Base 10 (decimal)
• Base 2 (binary )
• Base 8( octal)
  
• Base 16 ( hexadecimal)
• Base 256 (IP address)

 Note :-    Number = 789456  

Symbol  =    7   8  9  4  5  6 

Position  = 5  4  3  2  1  0

• Base 10  ( decimal) :-

The base 10 or decimal number system use 10 symbols : 0,1,2 ,3,4,5,6,7,8,9

Weight  = 10 position 

• Base 2 ( binary) :-

The base 2 or binary number system uses two symbols : 0,1 

Weight  = 2position 

• Base 8 ( octal) :-

The base 8 0r octal number system uses 8 symbols : 0,1,2,3,4,5,6,7

Weight  = 8position

• Base 16  ( hexadecimal) :- 

The base 16 or hexadecimal  number system uses 16 symbols :0,1,2,3,4,5,6,7,8,9 A  B  C  D  E  F

Weight   =  16position 

• Base 256 ( IP address) :-

The base 256 number system uses 256 decimal number raging from 0 to 255. It is used to represent ipv4 address where each symbol is separates the position.

For Example ,

IPv4 address : 192.168.1.1

Symbol :   192   168   1    1

position :  3   2    1   0  

weight : 2563  2562  2561  2560

    3.  Images :-

An image is also represented with a sequence of 0 and 1 . A digital image is made up of small units called pixels .Each pixels is assigned a bit pattern whose size depend on the nature of the image.

   4 .  Audio :- 

A  sound which lies within the human frequency range of 20 to 20000 hertz is called  audio . the sound is recorded with microphone  and then digitized  to represent in the form of bit patterns  . Its transmitted form is called an audio signal.

 computer networking :-

A computer network is a system in which multiple computers are connected to each other to share information and resources.

                                 OR

A network is a set of device connected by communication links. A node can be a computer , printer, or any other device capable of sending and/or  receiving data generated by other nodes on the network .

 

 

Characteristics of a Computer Network:-

• Share resources from one computer to another.

• Create files and store them in one computer, access those files from the other computer(s) connected over the network.

• Connect a printer, scanner, or a fax machine to one computer within the network and let other computers of the network use the machines available over the network.

Following is the list of hardware's required to set up a computer network.

• Network Cables
• Distributors
• Routers
• Internal Network Cards
• External Network Cards

what is SQL? let`s get easy full knoweledge and notes.

              

• what is SQL?
  

SQL is stands for structured query language. According to ANSI(  american national standard institutes) in 1986.It is the standard language for relational database management system .
basically sql stands for sturctured query language is a database management language relational database.
sql  isn`t a programming language ,its a query language.
some common relational database management system  that use sql are : Oracle , sybase ,microsoft sql server etc.
The standard  sql commands such as "select","Insert","Update"," Delete","Create","Drop" can be used to accomplish almost everything that one needs to do with a database.

   
                               Every table is divided into smaller entities called fields. The fields in the Customers table consist of CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country. A field is a column in a table that is designed to maintain specific information about every record in the table.

A record, also called a row, is each individual entry that exists in a table. For example, there are 91 records in the above Customers table. A record is a horizontal entity in a table.

• Uses of SQL:-
  

1. SQL is used to communicate with a databse.
2. sql statements are used to performs tasks such as update data on a database.
3. Retrieve data from a database .
4. SQL lets you access and manipulate database.
5. sql can create views in a database.
6. sql can set permission on tables procedures and users.

• Data Definition language (DDL):- :- 

The SQL-DDL contains set of commands, which sets up , chnages or removes/delete data sturctures from the database. These data structures can be tables or pther database objects.

• Data manipulation language(DML):-

The SQL-DML includes those commands , which are based on both the relational algebra and the tuple relational calculus . DML is a language that enales users to access or manipulate data. By data manipulation ,we mean:

1. The retrieval of information stored in the table .
   
2. The insertion of new rows with information into the table.
3. The modification of information stored into the table.
   

• DCL:-   Data control language.
• TCL:- Trasaction control language.  
  

what is rdbms ? easy nd full explanation let`s learn it.

   What is RDBMS?

      Rdbms signifies relational database management system.It is used to organise and manipulate the data like –Oracle,DB2,MS SQL server,My SQL etc.

                                            & nbsp;                    Therefore, rdbmses are subset of DBMSes .A relational database refer to a database that keep/store data in a structured format,using rows and columns. By this it easy to find  and retrieve specific values within the database the queries run across multiple tables at once by the rational structure.
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What is DBMS?

     DBMS signify database management system.  DBMS provides user's and programmer's a systematic way/organised to make , update & run data.

    What is table?

      Table is collection of related data entries which means that the table should contain column  and rows. Horizontal subset of the table knew as a row and  the vertical subset of the table knew as a column . 

  The rows in  the relation are not ordered.
   "Since relation is a set aren't ordered hence no ordering defined on tuples of relation".

    Meta data:-

             Data that describe the properties or characters of other data some of there  properties consist data.ex:- datatype - integer,chara char,float,double.

    Key:-

     An group of attributes in a table that identifies a tuple uniquely is known as a key.

Types of key are following:-

          

• Primary key:-

       Candidate key selected identify tuples/records uniquely.

•   Alternate key:--

       Candidate key that aren't select to be primary key . It can be any of keys.

• Foreign key:--

        Attributes or set of attribute within one relation that matches candidate key same relation.

• Secondary key:-

       Attribute or set of attribute used for compunction key accessing records, but not necessarily unique.

• Composite key:-

      If we use multiple attributes to create a primary key than that primary key is called composite key.

•  Candidate key:-

      A minimum set of attributes that uniquely identifies each occurrence of a tuple. Attributes of candidate can`t have null value.

• Advantage:-

     1. Support for acid trans action. 

     2.  Security

     3.  Data manipulation.

     4.  provides multiple interface.

     5.  Good integrity.

•    Disadvantages:-

     1  sharing of data is poor.
     2  inconsistent data.

     3  inflexibility.

     4  inforcement of standards are poor.