technical guptaji

Operators in C

2023-07-24T15:56:00.000+05:30

Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical operations, based on the value provided. C language is rich in built-in operators and provides various operators which are given below:

1. Arithmetic Operators

An arithmetic operator is used to perform mathematical calculations or operations such as Addition, subtraction, multiplication, division etc. on numerical values. The following arithmetic operators are:

+(Addition) is used to add two operands.

-(Subtraction) is used to subtract second operand from the first operand.

*(Multiplication) is used to multiple two/both operands.

/(Division) is used to divides the numerator by denominator.

%(Modular) is used to give remainder of after an integer division.

2. Relational Operators

Relational operators are used to describe the relation between two operands. or you can say that relational operators are used to compare two operands. These are also known as Conditional operators. The following Relational operators are:

== (double equal to) is used to checks if the values of two operands are equal or not. If yes, then the condition becomes true.

!= (not equal to) is used to checks if the values of two operands are not equal. If the values are not equal, then the condition becomes true.

> (Greater than) is used to checks if the value of left operand greater than the value of right operand. If yes, the condition becomes true.

< (Less than) is used to checks if the value of left operand less than the value of right operand. If yes, the condition becomes true.

>= (Greater than equal to) is used to checks if the value of left operand greater than or equal to the value of right operand. If yes, the condition becomes true.

<= (Less than equal to) is used to check if the value of right operand less than or equal to the value of right operand. If yes, the condition becomes true.

3. Logical Operators

Logical operators are used to perform the logical operations. or whenever we want to check multiple conditions then we can use logical operators as well. The following logical operators are:

&& (Logical AND) if both the operands are non-zero then the condition becomes true.

|| (Logical OR) if any of the two operands is non-zero then the condition becomes true.

! (Logical NOT) is used to reverse the logical state of its operand. If a condition is True than logical not operator will make it False.

File Operation-Writing

2023-01-09T15:11:00.003+05:30

Writing to the File

In C programming there are three functions used to write data into a file. If we want to write something into the file then we can use one of the function from the following functions:- fprintf(), fputs() and fputc() functions.

All the above functions are used to write the contents to a file.Let us discuss each of them one by one :-

1. fprintf() Function

The fprintf() function is used to write data to a file. It writes a set of character into a file.We can write other types of values like int, float etc. into a file by using this method.

Syntax

int fprintf(FILE *fp, char string[])

The fprintf() function accepts two arguments or parameters. The first one is file pointer which in indicating to the file and the second one is sequence of characters or you can say that array of character means a string.

Program Example

#include<stdio.h>

int main()

{

FILE *fp;

if(fp=fopen("hello.txt", "w"))

{

if(fprintf(fp,"c programming")>=0)

{

printf("write operation successful by using the fprintf function");

}

fclose(fp);

return 0;

}

2. fputs() Function

The fputs() function is used to write a single line of characters into a file. It is used to write a line (Character line) to the file.

Syntax

int fputs(char String[], FILE *fp);

It takes 2 arguments. The first argument is a string which is to be written into the file and the second argument is the pointer of the file means a file pointer in which the string is to be written. It returns 1 if the write operation was successful, otherwise, it returns 0.

Program Example

#include<stdio.h>

int main

{

FILE *fp;

if(fp=fopen("hello.txt","w"))

{

if(fputs("C Programming", fp)>=0)

{

printf("String written to the file successful");

}

fclose(fp);

return 0;

}

3. fputc() Function

The fputc() function is used to write a single character to the file.

Syntax

int fputc(char Character, FILE *fp);

It also takes 2 arguments. The first argument is a Character which is to be written in the file and the second argument is the pointer of the file means a file pointer in which the string is to be written. It returns 1 if the write operation was successful, otherwise, it returns 0.

Program Example

#include<stdio.h>

int main

{

FILE *fp;

if(fp=fopen("hello.txt","w"))

{

fputc('C', fp)>=0)

}

fclose(fp);

return 0;

}

Output

C will be written to the file.

File operations- Reading

2023-01-09T10:10:00.005+05:30

Reading from the File

In C programming we can read content of a file by using fscanf(), fgets() and fgetc() functions. All these functions are used to read the contents of a file. Let us discuss about those functions one by one :-

1. fscanf() Function

The fscanf() function is used to read character set means strings from the file. It returns EOF (End Of File), when all the content of the file are read by it. IT does not read spaces.

Syntax

fscanf(FILE *fp, const char string[])

The fscanf() method accepts two arguments or parameters. first one is a pointer of FILE type which is a file pointer and the other one is the string of character in which the characters are stored after reading from the file.

Program Example

#include<stdio.h>

int main()

{

FILE *fp;

char str[100];

fp=fopen("hello.txt", "r");

while(fscanf(fp,"%s",str)!=EOF)

{

printf("%s",str);

}

fclose(fp);

return 0;

}

2. fgets() Function

The fgets() function in C is used to read string from the stream. We can specify the number of characters which we want to read from the file by the fgets() function. Means we can read a string to a particular range of characters by using fgets() function. This method can read the spaces also.

Syntax

fgets(char *string, int length, FILE *fp);

The fgets() function accepts three parameters or arguments which are given below:-

char string : It is a string which will store the data after reading from the file.

int length : It is an integer which gives the length of string to be considered.

FILE *fp : It is the pointer to be opened file or you can say that a file pointer.

Program Example

#include<stdio.h>

int main()

{

FILE *fp;

char str[100];

if(fp=fopen("hello.txt","r"))

{

printf("%s", fgets(str, 50, file));

}

fclose(fp);

return 0;

}

3. fgetc() Function

The fgetc() function in C is used to return a single character from the file. IT gets a character from the file and return EOF at the end of the file. If we want to read only a single character from the file then we can use fgetc() function.

Syntax

fgetc(FILE *fp)

The fgetc() function accepts only a single parameter or argument that is a file pointer.

Program Example

#include<stdio.h>

int main()

{

FILE *fp;

char str;

if(fp=fopen("hello.txt","r"))

{

while((str=fgetc(fp))!=EOF)

{

printf("%c",str);

}

fclose(fp);

return 0;

}

File Handling In C

2023-01-07T10:30:00.006+05:30

File

A File represents a sequence of bites on the disk where the group of related data is stored.

File is a place on storage disk where a group of related data is stored.Files provides a way to store large volume of data that can be used whenever needed.

Types of File

C programming language supports two types of files and they are as follows :-

1. Text Files

The file that contains ASCII codes of data like digits, alphabets and symbol is called text file or ASCII file like txt file, doc file etc.

2. Binary Files

The file that contains data in the form of bytes (0's and 1's) is called as binary file. Generally, the binary files are compiled version of text files. like bin file.

File Handling

The process of file handling refers to the method of storing data on the disk in the C program in the form of and output or input that might have been generated while running a C program.

File handling in C enables us to create, update, read and delete the files stored on the local file system through our C program. The operations can be performed on a file are given below :-

1. Creation of the new file / Opening an existing file.

2. Reading from the file.

3. Writing to the file.

4. Closing a file/Deleting the file.

Let us discuss one by one:-

1. Creation of the new file/ Opening and existing file

A file can be created or an existing file can be opened by using fopen() function. It is a predefined function which is defined in the stdio.h headerfiles.

firstly, the fopen() function searches the file to be opened.If the file does not exist, it will be created newly in the location where the program is stored with the filename. Then it loads the file from the disk and place it into the buffer. The buffer is used to provide efficiency for the read operation. and sets up a character pointer which points to the first character of the file.

Syntax

FILE fopen(const char filename, const char mode);

The fopen function takes two arguments or parameters.

1. The filename (string) : If the file is stored at some specific location, then we must mention the full path at which the file is stored. For example : A file name can be like "C:folder/subfolder/filename.ext".

2. The mode (string) : The mode in which the file is to be opened. In C programming various modes are available which can be used with the fopen() function on the basis of what operation we wants to do on the file.

Example

FILE *fp;

fp=fopen("student.txt", "w");

In the above example, if the file "student.txt" does not exist, it will be created newly in the location where the program is stored because there is no path if given. If the file is already exists then contents will be deleted and opened as an empty file. Reading operation is not allowed on that file because the file is opened in "w" mode.

If we want to perform reading operation also on that file , then the file should be opened in "w+" mode like

fp=fopen("student.txt", "w+");

Program Example

#include<stdio.h>

int main()
{

FILE *fp;

if(fp=fopen("student.txt", "r"))

{

printf("file opened successfully in read mode");

}

else
{

printf("The file is not exist with that name");

}

fclose(fp);

return 0;

}

We can open the file one of the following modes by using fopen() function :-

"w" mode : Open a text file in write mode. If the file exists, its contents are overwritten and if the file does not exist, it will be created.

"r" Mode : Opens a text file in read mode. If the file does not exist, fopen() returns NULL. If the file exists, it can be read.

"a" Mode : Opens a text file in append mode. If the file does not exist, it will be created. If the file exists, contents can be added to the end of the file.

"w+" Mode : Open for both reading and writing. If the file exists, its contents are overwritten, if the file does not exist, it will be created.

"r+" Mode : Open for both reading and writing. If the file does not exists, fopen() returns NULL, if the file exist, the contents can be read.

"a+" Mode : Open for both reading and appending. If the file does not exist, it will be created. If the file exists, the contents can be added to the end of the file.

"rb" Mode : Opens a binary file in read mode.

"wb" Mode : Opens a binary file in write mode.

"ab" Mode : Opens a binary file in append mode.

Closing a File

Whenever we want to close the file we can use fclose() function. The fclose() function is used to close a file. The file must be closed after all the operations on it.

Syntax

fclose(FILE *fp);

Dynamic Memory Allocation in C

2023-01-04T15:49:00.010+05:30

Dynamic Memory Allocation

Dynamic Memory Allocation means Memory allocated at runtime.

Dynamic Memory Allocation can be defined as a procedure in which the size of data structure (like array)is changed during the runtime.

C programming provides some functions to achieve the Dynamic Memory allocation.

There are 4 library functions provided by C defined under the <stdlib.h> header file.The functions are:

1. malloc()

2. calloc()

3. realloc()

4. free()

1. malloc() function

The malloc means memory allocation method in C is used to allocate a single large block of memory dynamically with the specified size in bytes. malloc() functions returns a generic void pointer which can be cast into a pointer of any form.

It has initialized each block with the default garbage value initially.The memory will initialize in the Heap section.

Generally we use malloc function to locate the memory for structures.

Syntax

ptr= (cast-type*) malloc (byte-size);

Example

ptr= (int*) malloc (20*sizeof(int));

This statement will allocate 80 bytes ( since the size of int is 4 bytes) of memory.and the pointer ptr holds the address of the first byte in allocated memory (base address).

It returns NULL if memory is not allocated or not sufficient.

Program Example

#include<stdlib.h>

#include<stdio.h>

int main()

{

int n,i,*ptr,sum=0;

printf("Enter number of elements:");

scanf("%d",&n);

ptr=(int*) malloc (n*sizeof(int));

if(ptr==NULL)

{

printf("Sorry unable to allocate memory");

exit(0);

}

printf("enter elements of array:");

for(i=0;i<n;i++)

{

scanf("%d", ptr+i);

sum+= *(ptr+i);

}

printf("sum=%d", sum);

free(ptr);

return 0;

}

Output

Enter number of elements : 3

Enter elements of array : 10 11 12

sum=33

2. calloc() function

calloc means contiguous allocation method in C is used to dynamically allocate the specified number of blocks of memory of the specified type.

this method is very much similar to malloc() but has some differences are given below :-

It has two parameters or arguments as compare to malloc() function which has only one parameter.
calloc() method allocate the multiple blocks of specified size.
It initializes each block with a default value '0'.

Syntax

ptr=(cast-type*) calloc(n, element-size);

Here, n is the number of elements and element-size is the size of each block.

Example

ptr=(float*)calloc(25,sizeof(float));

This statement allocates contiguous blocks in memory for 25 elements each with the size of the float.

If space is insufficient, allocation fails and returns a NULL pointer.

Program Example

# include<stdio.h>
#include<stdlib.h>
int main()
{
int *ptr, n, i;
printf("Enter the number of elements in the array:");
sacnf("%d", &n);
ptr=(int*)calloc(n,sizeof(int));
if(ptr==NULL)
{
      printf("memory is not allocated:\n");
      exit(0);
     }
else
{
      printf("Memory successfully allocated using calloc:\n");
      for(i=0;i<n;++i)
      {
          ptr[i]=i+1;
      }
         printf("The elements of the array are:");
         for(i=0;i<n;++i)
         {
              printf("%d",ptr[i]);
          }
       }
   return 0;
}

Output

Enter the number of elements in the array : 5

Memory successfully allocated using calloc

The elements of the array are : 2 5 4 6 8

3. realloc() function

realloc means Re-allocation method in C is used to dynamically change the memory allocation of a previously allocated memory. We can say if the memory previously allocated with the help of malloc() or calloc() function is insufficient, realloc() function can be used to re-allocated the memory dynamically.

re-allocation of memory maintains the already present value and new blocks will be initialized with the default value.

Syntax

ptr=realloc(ptr, newsize);

where ptr is reallocated with the new size "newsize".

Example

int *ptr=(int*)malloc(5*sizeof(int));

This statement will allocate a single memory block of 20 bytes(if the integer size will be 4 bytes) and allocated to ptr.

If we want to change the memory allocated to ptr then we can use realloc() function to change the allocated memory dynamically.

ptr=realloc(ptr, 10*sizeof(int));

By using this statement the size of ptr is changed from 20 bytes to 40 bytes dynamically and allocated to ptr.

Program Example

#include<stdio.h>

#include<stdlib.h>

int main()

{

int *ptr, n, i;

printf("Enter the number of elements in the array:");

scanf("%d", &n);

ptr=(int*)calloc(n,sizeof(int));

if(ptr==NULL)

{

printf("Memory not allocated\n");

exit(0);

}

else

{

printf("Memory successfully allocated\n");

for(i=0;i<n;++i)

{

ptr[i]=i+1;

}

printf("The elements of the array are:");

for(i=0;i<n;++i);

{

printf("%d",ptr[i]);

}

printf("Enter the new size :");

scanf("%d", &n);

ptr=realloc(ptr, n*sizeof(int));

printf("Memory successfully re=allocated\n");

for(i=0;i<n;++i)

{

ptr[i]=-i+1;

}

printf("The elements of the new array are:");

for(i=0;i<n;++i)

{

printf("%d", ptr[i]);

}

free(ptr);

}

return 0;

}

4. free() function

The free() method in C programming is used to dynamically de-allocate the memory which is allocated by the calloc() or malloc() method. It helps to reduce the wastage of memory.

The memory occupied by malloc() or calloc() functions must be released by calling free() function. If we do not free the memory which is already allocated than it will consume memory until program exit.

Syntax

free(ptr);

Note : If we will try to access the memory location which has been de-allocated by using free() function then it will show you an undefined behavior.

Array In C Programming

2022-12-03T10:06:00.003+05:30

Array

An Array is defined as the collection of similar types of data item stored at contiguous memory locations.

Array are the derived data types in C programming language which can store the basic data types such as int, char, float, double etc.

An array can be One Dimensional, Two Dimensional or Multi Dimensional. The C language places no limits on the number of dimensions in an array. A one dimensional array is like a list and a two dimensional array is just like a matrix in the form of rows and columns.

All array elements consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address corresponds to the last address.

Python IDE

2022-05-31T15:38:00.004+05:30

IDE

IDE stands for Integrated Development Environment is defined as a coding tool that helps to automate the process of editing, compiling, testing etc. in an SDLC and provides ease to developer to run, write and debug the code.

It is specially designed for software development that consists of several tools which is used for developing and testing the software.

There are some Python IDE's which are as follows :

PyCharm

Spyder

PyDev

Wing

Thonny

Jupyter Notebook

Microsoft Visual Studio

Eric

PYCHARM

PyCharm was developed by the Jet Brains, and it is a cross-platform integrated development environment specially designed for python. it is the most widely used IDE and available in both paid version and free open source as well. It saves ample time by taking care of routine tasks.

It is a complete python IDE that is loaded with a rich set of features like auto code completion, quick project navigation, fast error checking and correction, remote development support., database accessibility etc.

Features

Smart code navigation

Errors Highlighting.

Powerful Debugger

Supports python web development frameworks, i.e., Angular JS, Java Script.

SPYDER

Spyder is an open source that has high recognition in the IDE market and most suitable for data science. The full name of Spyder is Scientific Python Development Environment. It supports all the significant platforms like Linux, Windows, and MacOS, Etc.

It provides a set of features like localized code editor, document viewer, variable explorer, integrated console etc. and supports number of scientific modules like NumPy, SciPy etc.

Features

Proper syntax highlighting and auto code completion.

Integrates strongly with IPython console.

performs well in multi-language editor and auto code completion mode.

PYDEV

PyDev is defined as one of the commonly used Python IDE, which is an external plugin for Eclipse. It is a natural choice of the Python Developers that are coming from the Java background and very popular in the market as Python interpreter.

Features

Strong parameters like refactoring, debugging, code analysis and code coverage function.

It supports virtual environments, MyPy, and block formatter.

Also supports PyLint integration, remote debugger, Unit test integration, etc.

WING

It is defined as a cross-platform IDE that is packed with necessary features and with decent development support. Its personal edition is free of cost. The pro version comes with a 30 days trial for the developers to try it out.

It has several features that include auto-completion, syntax highlighting, indents, and debugging.

Features

Customized and can have extensions as well.
Supports remote development, test-driven development along with the unit test.

THONNY

Thonny is another IDE which is best suited for learning and teaching programming. it is a software developed at the University of Tartu and supports code completion and highlight syntax errors.

Features

simple debugger

supports highlighting errors and auto code completion

JUPYTER NOTEBOOK

Jupyter is one of the most used Python notebook editors hat is used across the data science industry. It is a web application that is based on the server-client structure and allows you to create and manipulate notebook documents. It makes the best use of the fact that Python is an interpreted language.

Features

Support markdowns

Easy creation and editing of codes

Ideal for beginners in data science

MICROSOFT VISUAL STUDIO

Microsoft Visual Studio is an open source code editor which was best suited for development and debugging of latest web and cloud product. It has its own marketplace for extensions.

Features

Supports Python coding in Visual Studio

Available both paid and free version

ERIC PYTHON

The Eric Python is an editor which is developed in Python itself and can be used for both professional and non-professional work.

Features

Advanced project management capability, version control

In-built debugger and task management support.

Offers configurable window layout, editors, source code folding.

Variable in C Programming

2021-12-15T09:59:00.006+05:30

Variable

A variable is a name of memory location. It is used to store data. Value can be changed, and it can be reused many times.

It is way to represent memory location through symbol so that it can be easily identified.

Syntax : Data-Type Variable-Name;

Example

int a;

float b;

char c; Here a,b,c are variables.

Note : We can also provide values while declaring the variables.

Example

int a=10, b=20;

float f=20.2;

char c='B';

Types of variables

There are various types of variables are available in C programming language. which are discussed below :

1. Local Variable

A variable that is declared inside the function or block is called a local variable.It must be declared at the start of the block.

You must have to initialize the local variable before its first used.

The scope of local variable is always local. Means we can access from only inside the function.

Example

void function()

{

int x=10; // Local Variable

}

2. Global Variable

A variable that is declared outside the function or block is called a global variable. Any function can change the value of a global variable.

It must be declared outside of the block.

The scope of global variable is always global means we can access from anywhere through out the program.

Example

int value=10; // Global variable

void function()

{

int x=30; // Local variable

}

3. Static Variable

A variable that is declared with the static keyword is known as Static Variable. It retains its value between function calls.

Static variable can be defined inside or outside the function.The default value of static variable is zero.

Example

void function1()

{

int x=10; // Local Variable

static int y=15; // Static Variable

x=x+1;

y=y+1;

printf("%d,%d",x,y);

}

In the above example if you call the function many times, the local variable will print same value for each function but the static variable will print the incremented value in each function call.

4. Automatic Variable

All variables in C that are declared inside the block, are automatic variables by default. But if we want to explicitly declare a variable as an automatic variable then we can do with the help of auto keyword.

Automatic variables are similar as local variables.

Example

void main()

{

int x=10; // Local Variable

auto int y=15; // Automatic Variable

}

They both are automatic variables but the difference is that the y is explicitly declared as an automatic variable with the help of auto keyword.

5. External Variable

These variables are defined outside the function. We can share a external variable between multiple C files.External variables can be declared number of times but defined only once.

We can declare external variable with the help of extern keyword.Default value of external variable is zero.

Switching Techniques in Computer Network

2021-12-08T10:04:00.004+05:30

Switching

In large networks, there may be more than one paths exist for transmitting data from sender to receiver.The process of selecting a best path for sending the data from sender to receiver is known as Switching. Switching in a computer network is achieved by using a small hardware device that is called switch which is used to join multiple computers together with one Local Area Network.

The process of moving the data packets towards their destination by forwarding them from one port to the other port is called as switching.

To reduce the collision between packets we use switching. Packet Collision in minimum as it directly communicates between source to destination.

It increases the overall performance of the network by reducing the traffic on the network.

Switching Techniques

Switching technique is used to connect the systems for making one-to one communication. There are various following techniques are available which are given below :

Circuit Switching

Circuit switching is a method of implementing a telecommunication network in which two network nodes establish a dedicated path.In Circuit switching a complete end-to-end path must exist before the communication takes place.

In Circuit switching technique a dedicated path is established between sender and receiver before starting the transmission of packets. and that dedicated path will remain to exist until the connection is terminated.

When any user wants to send the data it may be in the form of voice, video, etc. then it sends a request signal if the path is exist then receiver sends back an acknowledgement to the sender to ensure the availability of the dedicated path. After receiving the acknowledgment, dedicated path transfers the data.

Circuit switching technique is used in public telephone network. It is used for voice transmission.

Communication by using circuit switching has 3 phases :

Connection Establishment (Circuit Establishment) : In this phase a circuit (Path) is established between one node to another node. Circuit provides a full dedicated path to travel the data from source to destination.

Data Transfer : After the connection establishment the entire data are sent through dedicated path (circuit)from source to destination.

Connection Termination : After the completion the process of sending data the circuit is disconnected means the connection between two nodes has terminated.

Total time taken to transmit a message in circuit switched network

= Connection set up time + Transmission Time + Propagation Time + Tear down time

Advantages

Before transmit the data a full dedicated path is established to travel the data.

Data is transmitted without any delay because there is no waiting time at any switch.

Receiver always receives the data in the order. in order.

No re ordering is required.

Disadvantages

The set up required time ( for connection establishment) is too long.

Dedicated channels require more bandwidth.

It is more expensive than other switching techniques.

Routing decisions (The path between two nodes) can not be changed once the circuit is established.

Circuit Switching can use two types of technologies which are :-

Space Division Switches :

In space division switching, a dedicated path is established between the source and destination for the entire period of transmission.

Space Division Switching can be achieved by using crossbar switch. A crossbar switch is a metallic crosspoint or semiconductor gate that can be enabled or disabled by a control unit. This requires separate physical path for each signal connection.

Time Division Switches

The incoming and outgoing signals when received and re-transmitted in a different time slot, is know as Time Division Switching.

In the Time Division switching, sampled values of speech signals are transferred at fixed intervals.The Time Division Switching may be analog or digital.

Time Division Switching uses time-division multiplexing to achieve switching means different ongoing connections can use same switching path but in different time interval.There are two popular methods for Time Division Switching namely Time Slot Interchange (TSI) and the TDM bus.

Channelization Protocols

2021-12-03T13:04:00.005+05:30

Channelization Protocols

Channelization or some times called channel Partition(Division) is a multiple access method in which the available bandwidth of a link is shared in respect with the time , frequency or through codes. It is a channelization protocol that allows the total usable bandwidth in a shared channel to be shared across multiple stations based on their time, distance and codes. It can access all the stations at the same time to send the data frames to the channel. There are three channelization protocols which are as follows : FDMA, TDMA and CDMA.

FDMA (Frequency Division Multiple Access)

This method is used to divide the available bandwidth into equal frequency bands by which multiple users can send data through a different frequency to the subchannel. Each station is allocated a band to send its data.In other words, each frequency bands is reserved for a specific station. Each station also uses a band pass filter to confine the transmitter frequencies. To prevent station interference, the allocated bands, are separated from one another by using a small guard bands. Small guard can reduce the cross talk only not remove it.

TDMA (Time Division Multiple Access)

In Time division Multiple Access method, the stations share the bandwidth of the channel in time. Each station is allocated a time slot during which it can send the data. Each station transmits its data in its assigned time slot.

No Guard Band are required in the Time Division Multiple Access.

CDMA (Code Division Multiple Access)

In CDMA, all stations can simultaneously send the data over the same channel. It means that it allows each station to transmit the data frames with full frequency on the shared channel at all times. It does not require the division of bandwidth on a shared channel based on time slots. If multiple stations send data to a channel simultaneously, their data frames are separated by a unique code sequence. Each station has a different unique code for transmitting the data over a shared channel. For example, there are multiple users in a room that are continuously speaking. Data is received by the users if only two-person interact with each other using the same language. Similarly, in the network, if different stations communicate with each other simultaneously with different code language.

Multiple Access Control in data link layer

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Multiple Access Control

When multiple nodes or stations are connected together by using a common link to transmit data packets or frames. Every node or station are free to transmit the data frame at one time.In that case, multiple stations can access the channel and simultaneously transmits the data over the channel. It may create collision Hence, the multiple access protocol is required to reduce the collision.

For example,Let us assume that there is a classroom full of students.When a teacher asks a question to the students then all the students available in that class start answering the question at the same time. Because all the students respond at the same time so here is very high chances that the data will be overlap or data lost.Therefore it is the responsibility of a teacher which will be act as multiple access protocol to manage the students and make them one student can answer at a time.

To reduce the problem of collision we use the various Multiple Access Protocols :

Random Access Protocols

In random access protocol, no station is superior to another station and none is assigned control over another.This decision depends on the state of the medium (Idle or Busy).

This method gives us two features:

The First is there is no schedule time for station to transmit the data. Transmission is random among the stations that is why it is called Random Access.

The Second is, no rules specify which station should send next. Station compete one another to access the medium. That is why these methods are also called Contention methods. In random access method,each station has right to the medium without being controlled by any other station. However. if more than one station tries to send, there is an access conflict-collision and the frames will be either destroyed or modified(Corrupted).

There are various methods for random access protocols which are given below :

ALOHA (Pure ALOHA and Slotted ALOHA)

CSMA

CSMA/CD

CSMA/CA

ALOHA

ALOHA, the earliest random access method was developed at the University of Hawaii in 1970. It was designed for a radio(wireless) LAN, but it can be used on any shared medium. The medium is shared between the stations. When a station sends a data, another station may attempt to do so at the same time. The data from the stations collide and become garbled.

In this Any station can transmit data to a channel at any time. It does not require any carrier sensing. It require transmission of data after some random amount of time.It can be of two types :

Pure ALOHA

The original ALOHA protocol is called pure ALOHA. This is a simple but elegant protocol.However, since there is only one channel to share, there is the possibility of collision between frames from different station.

If you have data to send, send the data.

If, while you are transmitting data, you receive any data from another station, there has been a message collision. All transmitting stations will need to try resending "later".

In pure ALOHA, each station transmits data to a channel without checking whether the channel is idle or not, the chances of collision may occur, and the data frame can be lost.

When any station transmits the data frame to a channel, the pure Aloha waits for the receiver's acknowledgment. If it does not acknowledge the receiver end within the specified time, the station waits for a random amount of time, called the backoff time. And the station may assume the frame has been lost or destroyed. Therefore, it retransmits the frame until all the data are successfully transmitted to the receiver.Below figure shows an example of frame collision in pure ALOHA.

There are four stations that contend with one another for access to the shared channel. In this figure each stations sends two frames, there are total of eight frames on the shared medium.Some of these frames collide because multiple frames are in contention for the shared channel. Only two frames survive: one frame from station 1 and one frame from station 3.we need to resend the frames that have been destroyed during transmission.If all these stations try to resend their frames after the time-out the frames will collide again.Pure ALOHA dictates that when the time-out period passes, each station waits a random amount of time before resending its frame. The randomness will help to avoid more collision. We call this time the back off time.

Slotted ALOHA

Slotted ALOHA was invented to improve the efficiency of Pure ALOHA. In slotted ALOHA we divide the time into equal time intervals called slots and forces the station to transmit the data only at the beginning of the time slot and only one frame is allowed to be sent to each slot.And if the stations are unable to send data at the beginning of the slot, the station will have to wait until the beginning of the slot for the next time.

However, the possibility of a collision remains when trying to send a frame at the beginning of two or more station time slot.Below figure shows an example of frame collision in slotted ALOHA.

Because a station is allowed to send only at the beginning of the time slot. If a station misses this moment it must wait until the beginning of the next time slot. This means that the station in which started at the beginning of this slot has already finished sending its frame. There is still the possibility of collision if two stations are try to send at the beginning of the same time slot.

CSMA (Carrier Sense Multiple Access)

To minimize the chance of collision and therefor increase the performance, the CSMA method was developed. The chance of collision can be reduced if a station senses the medium before trying to use it. CSMA method requires that each station check the state (Idle or Busy) of the medium before sending the frame.

It means that if the channel is idle, the station can send data to the channel. Otherwise, it must wait until the channel becomes idle. Hence, it reduces the chances of a collision on a transmission medium. In other words, CSMA is based on the principle "Sense before transmit". CSMA may reduce the possibility of collision.

The possibility of collision still exists because of propagation delay : when a station sends a frame, it still takes time for the first bit to reach every station and for every station to sense it. In other words, a station may sense the medium and find it idle, only because the first bit sent by another station has not yet been received.

There are three methods proposed for CSMA which tells us that what should a station do if the channel is Busy or Idle which are given below.

I-Persistent : The I-Persistent method is very simple. In this method, a station continuously sense and after the station finds the line idle.It sends its frame immediately. This method has the highest chance of collision because two or more stations may find the line idle and send their frames immediately at the same time.

Non Persistent : In this method, a station that has a frame to send sense, if the line is idle, it sends immediately. but if the line is busy, it waits a random amount of time and sense the line again.The Non Persistent method reduces the chance of collision because it is unlikely that two or more stations will wait the same amount of time and retry to send on the same time.

P-Persistent : The P-Persistent method is used if the channel has the time slot duration equal to or greater than the maximum propagation time.This method is the combination of two other persistent methods.It reduces the chance of collision and improves efficiency.

CSMA/CD

It is a carrier sense multiple access/ collision detection network protocol to transmit data frames.The CSMA method does not specify the procedure following a collision. CSMA/CD augments the algorithms to handle the collision. In this methods the station monitors the medium after it sends a frame to see if the transmission was successful. If so the station has finished , if there is a collision , the frame is sent again.

It first senses the shared channel before broadcasting the frames, and if the channel is idle, it transmits a frame to check whether the transmission was successful. If the frame is successfully received, the station sends another frame. If any collision is detected in the CSMA/CD, the station sends a jam/ stop signal to the shared channel to terminate data transmission. After that, it waits for a random time before sending a frame to a channel.

CSMA/CA

It is a Carrier Sense Multiple Access/Collision Avoidance network protocol for carrier transmission of data frames. It was invented for wireless network.It receives an acknowledgment when a data frame is sent to check whether the channel is clear or not. If the station receives only a single (own) acknowledgments, that means the data frame has been successfully transmitted to the receiver. But if it gets two signals (its own and one more in which the collision of frames), a collision of the frame occurs in the shared channel. Detects the collision of the frame when a sender receives an acknowledgment signal.

There are three strategies to avoid the collision which are given below :

Inter Frame Space(IFS)

In this method, the station waits for the channel to become idle, and if it gets the channel is idle, it does not immediately send the data. Instead of this, it waits for some time, and this time period is called the Inter Frame Space or IFS. However, the IFS time is often used to define the priority of the station.

Contention window

In the Contention window, the total time is divided into different slots. When the station/ sender is ready to transmit the data frame, it chooses a random slot number of slots as wait time. If the channel is still busy, it does not restart the entire process, except that it restarts the timer only to send data packets when the channel is inactive.

Acknowledgment

In the acknowledgment method, the sender station sends the data frame to the shared channel if the acknowledgment is not received ahead of time.

Flow Control in Data Link Layer

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Flow Control

Data Link layer provides a functionality to control the flow of the data between two nodes is called Flow Control. Flow control in the data link layer is a technique that allows two stations working at different speeds to communicate with each other.

If the sender is on a fast and powerful computer as compared to the receiver then the receiver may get overwhelmed by the frames transmitted by the sender.In such a scenario even if there is no error in the transmission of the frame the receiver may lose some of the frames as it is unable to process the frame with the speed at which the sender is transmitting the frame.

In the data link layer, flow control restricts the number of frames that sender can send before it waits for an acknowledgement from the receiver.

It is a set of measures taken to regulate the amount of data that a sender sends so that a fast sender does not overwhelm a slow receiver.

If there is no flow control mechanism present then after some time the data buffer at the receiver end may get full and overflow as the data link at the receiver may be busy in processing the old received data. In this process, the receiver may lose some frames or data transmitted from the sender. To fix this problem there are two approaches to flow control.

1. Feedback-based Flow Control

2. Rate-based Flow Control

1. Feedback-based Flow Control

In these protocol, the sender sends frames after it has received acknowledgement for the previous sent frame from the receiver. This is used in Data Link Layer.

2. Rate-based Flow Control

These protocols have built in mechanisms to restrict the rate of transmission of the data without requiring acknowledgement from the receiver. This is used in the Network Layer and Transport Layer.

Flow Control techniques in Data Link Layer

Data link layer uses feedback based flow control mechanisms. There are basically two types of techniques to control the flow of data:-

Stop and Wait Flow Control

This method is easiest and simple form of flow control.In this method the following transitions are involved −

The sender sends a frame and stop transmitting until the acknowledgement of the sent data-frame is received.

Once the receiver receives the frame, it sends an acknowledgement back to the sender.

On receiving the acknowledgement, the sender understands that the receiver is ready to accept the next frame. So it send another frame after receiving the acknowledgement from the receiver.

Advantages –

This method is very easy and simple and very accurate.
Each of the frames is checked and acknowledged well.
It can also be used for noisy channels.

Disadvantages –

This method is very slow in compare to other techniques.
In this method, only one frame can be sent at once.
It is very inefficient and makes the transmission process very slow.

Case 1 : Data frame is lost during transmission between sender to receiver.

Sender will think that receiver is busy to accept the fame but actually data is lost.

Receiver will assume no packet has been sent by the sender.

Both will be waiting for each other(sender waits for the acknowledgement and the receiver waits for the data frame) and there will be a deadlock.

Solution : A timer is applied between sender and the receiver and the receiver will wait till timeout timer for the data after that it will confirm that data has been lost.

Case 2 : Acknowledgement lost during transmission between receiver to sender.

After timeout timer expires, sender will assume that the data is lost but actually the acknowledgement is lost. By assuming this it will send the data frame again to the receiver receiver will think that, it is a new frame, hence it will send acknowledgement again so that will be have duplicate data packet.

Solution : To remove duplicate data packet problem a method is introduced that is called "sequence number". which are added to the every data frame. so using frame numbers receiver can easily determine the duplicates frames.

Sliding Window Flow Control

The sliding window protocol is a technique to send the multiple frames at once. In this protocol sender and the receiver both are agree upon the total number of data frames after which acknowledgement is needed to be transmitted. In this method the sender can send various data frames without getting an acknowledgement.

In this method we use sequence numbers for each data frame to avoid duplicate frame received at the receiver side. Each frame has sent according to there sequence number.

This increases and improves network throughput. Sliding window method also known as Windowing.

Sliding window protocol has two types :

1. Go-Back-N ARQ(Automatic Repeat Request)

2.Selective Repeat ARQ

1. Go-Back-N Protocol

It is the type of sliding window protocol means here sender can sent multiple frames at once. In this protocol N is the size of the sender window and the receiver window size is always 1. For example, Go-Back-8, the size of sender window will be 8.

Sender can send multiple frames at once but the receiver can receive only one frame at once because the frame size of receiver is only 1..There is no acceptance of out of order frames.Frames are only accept in order.

In this method a receiver does not receive a corrupted frame if receiver has a frame which is corrupted then it cancels to receive it and when the timer expires, the sender sends the correct frame again.

In this method we use cumulative acknowledgement. means receiver send the acknowledgement for the next expected frames means if receiver has received frame 1, frame 2 and frame 3 then it will send acknowledgement 4 for next expected frame.

In this method the retransmission is very high because the receiver can only receive one frame at once while the sender can send multiple frames at once so if any one of the frame is lost during transmission then receiver waits for that frame and do not receive any other frame before that frame. If the acknowledgment of a frame is not received within the time period, then sender has to be send all frames from starting.

2. Selective Repeat Protocol

Selective Repeat Protocol is also a type of sliding window protocol in which we can transmit the multiple number of frames at once.In this protocol, the size of the sender window is always same to the receiver window size.means the receiver also can receive multiple frames at once without sending a acknowledgement. It can accept out of order frames also.

If the receiver has a corrupt frame, it does not directly cancels it. It sends a negative acknowledgment to the sender. The sender sends that frame again as soon as on the receiving negative acknowledgment. There is no waiting for any time-out to send that frame.

The retransmission is very low in this method.It is more complex to implement because it uses searching and sorting techniques.

Advantages:

Retransmission is very low compare to Go-Back-N protocol.

Disadvantages:

More complexity of sender and receiver.
Each frame must be acknowledge individually because there is no cumulative acknowledgements.
Receive may receive frames out of sequence.

Error Correction Techniques

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Error detection techniques is used to find out the exact number of bits that have been corrupted and as well as their locations.

Error correction can be handled in two ways :

1. Backward Error Correction (Retransmission) : If the receiver detects an error in the incoming data unit, it requests the sender to re-transmit the data frame. It is a relatively simple technique. But it can be efficiently used only where retransmitting is not expensive as in fibre optics.

2. Forward Error Correction : If the receiver detects some error in the incoming frame, it executes error correcting code that generates the actual frame. This saves bandwidth required for retransmission.

If there are two many errors, the frames need to be retransmitted.

A single additional bit can detect the error, but cannot correct it.

For correcting the errors, one has to know the exact position of the error. For example, if we want to calculate a single bit error, the error correction code will determine which one of seven bits is in error. To achieve this, we have to add some additional redundant bits.

Redundant bits : Redundant bits are extra binary bits that are generated and added to the information carrying bits of data transfer to ensure that number of bits were lost during the data transfer.

Suppose r is the number of redundant bits and d is the total number of data bits. The number of redundant bits r can be calculated by using the formula:

Number of redundant bits 2^r>=d+r+1

The value of r is calculated by using the above formula. For example, if the value of d is 4, then the possible smallest value that satisfies the above relation would be 3.

To determine the position of the bit which is in error, a technique developed by R.W Hamming is Hamming code which can be applied to any length of the data unit and uses the relationship between data units and redundant units.

Hamming Code

Hamming Code is a set of error correction code that can be used to detect and correct the errors that can occur when the data is moved from sender to the receiver.

Parity Bits : A parity bit is a bit appended to the data of binary bits to ensure that the total number of 1's in the data is even or odd. Parity bits are used for error detection.

There are two types of parity bits :

Even parity: To check for even parity, if the total number of 1's is even, then the value of the parity bit is 0. If the total number of 1's is odd, then the value of the parity bit is 1.

Odd Parity: To check for odd parity, if the total number of 1's is even, then the value of parity bit is 1. If the total number of 1's is odd, then the value of parity bit is 0.

Algorithm of Hamming Code

Step 1 : Calculate the number of redundant bits by using this formula 2^r>=d+r+1.

Step 2 : Find out the positions of redundant bits.

The redundant bits placed at bit positions of powers of 2 like 1,2,4,8,16,32.... and so on.

Step 3 : calculate the values of each redundant bits.

Each redundant bit, r is calculated as the parity, generally even parity, based upon it's bit position.

Step 4 : Placed the redundant bits into the positions of actual data and sent to the receiver.

Step 5 : At the receiver's end the parity bits are also calculated and if the parity bits having non-zero values then the data is said to be corrupted.

Step 6 : Find out the position of the data which is corrupted and correct them by changing the bit to 0 or 1.

Example : Suppose the original data is 1010 which is to be sent.

At the first step we calculate the number of redundant bits

Total number of data bits 'd' = 4

Number of redundant bits r 2^r >= d+r+1

2^r>= 4+r+1

Therefore, the value of r is 3 that satisfies the above relation. So there we will use 3 redundant bits.

At the second step determine the positions of redundant bits.

The three bits are represented by r1, r2, r4. The position of the redundant bits is calculated with corresponds to the raised power of 2. Therefore, their corresponding positions are 1, 2¹, 2².

The position of r1 = 1

The position of r2 = 2

The position of r4 = 4

Representation of Data on the addition of parity bits:

At the third step determine the values of each redundant(parity) bits so now we find the values of r1, r2 and r4 by the help of this binary representation of every position number.

Determining the r1 bit

The r1 bit is calculated by performing a parity check on the bit positions whose binary representation includes 1 in the first position.

We observe from the above figure that the bit positions that includes 1 in the first position are 1, 3, 5, 7. Now, we perform the even-parity check at these bit positions. The total number of 1 at these bit positions corresponding to r1 is even, therefore, the value of the r1 bit is 0.

Determining r2 bit

The r2 bit is calculated by performing a parity check on the bit positions whose binary representation includes 1 in the second position.

We observe from the above figure that the bit positions that includes 1 in the second position are 2, 3, 6, 7. Now, we perform the even-parity check at these bit positions. The total number of 1 at these bit positions corresponding to r2 is odd, therefore, the value of the r2 bit is 1.

Determining r4 bit

The r4 bit is calculated by performing a parity check on the bit positions whose binary representation includes 1 in the third position.

We observe from the above figure that the bit positions that includes 1 in the third position are 4, 5, 6, 7. Now, we perform the even-parity check at these bit positions. The total number of 1 at these bit positions corresponding to r4 is even, therefore, the value of the r4 bit is 0.

At the step 4 placed the redundant bits into the positions of actual data and sent to the receiver.now the the transferred data is :

Suppose the 4^th bit is changed from 0 to 1 at the receiving end, then parity bits are recalculated at the receiver site in the step 5.

R1 bit

The bit positions of the r1 bit are 1,3,5,7.

We observe from the above figure that the binary representation of r1 is 1100. Now, we perform the even-parity check, the total number of 1's appearing in the r1 bit is an even number. Therefore, the value of r1 is 0.

R2 bit

The bit positions of r2 bit are 2,3,6,7.

We observe from the above figure that the binary representation of r2 is 1001. Now, we perform the even-parity check, the total number of 1's appearing in the r2 bit is an even number. Therefore, the value of r2 is 0.

R4 bit

The bit positions of r4 bit are 4,5,6,7.

We observe from the above figure that the binary representation of r4 is 1011. Now, we perform the even-parity check, the total number of 1's appearing in the r4 bit is an odd number. Therefore, the value of r4 is 1.

Note : If we get all the parity bits are 0 at the receiver end then the data is not corrupted.

But here we get the non-zero parity bits so here is an error or the data is said to be corrupted.

The binary representation of redundant bits, i.e., r4 r2 r1 is 100, and its corresponding decimal value is 4. Therefore, the error occurs in a 4^th bit position. The bit value must be changed from 1 to 0 to correct the error.

Error Control in Data Link layer

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Error Control

Error control in data link layer is the process of detecting and correcting data frames that have been corrupted or lost during transmission.

In case of lost or corrupted frames, the receiver does not receive the correct data-frame and sender is ignorant about the loss. Data link layer follows a technique to detect transit errors and take necessary actions, which is re-transmission of frames whenever error is detected or frame is lost. The process is called Automatic Repeat Request (ARQ).

Error control can be done in two ways.

1. Error Detection : Error detection involves checking whether any error has occurred or not.The number of error bits and the type of error does not matter.

2. Error Correction : Error correction involves finding or calculating the exact number of bit's that has been corrupted and the location of the corrupted bit's.

For both Error detection and Error correction, the sender needs to send some additional bits along with the data bits.

The receiver performs necessary checks based upon the additional redundant bits. If it finds that the data is free from errors, it removes the redundant bits before passing the message to the upper layer.

Error Detection Techniques

There are four main techniques for detecting errors in frames namely Parity Check, Checksum, CRC and LRC.

1. Parity Check

The parity check is done by adding an extra bit, called Parity bit to the data to make a number of 1's either even in case of even parity or odd in case of odd parity.

Parity check also known as "Vertical Redundancy Check"(VRC). In this method, a redundant bit also called parity bit is added to each data unit.

This method include even parity and odd parity.Even parity means the total number of 1's in data is to be even and odd parity means the total number of 1's in data is to be odd.

While creating a frame, the sender counts the number of 1's in it and adds the parity bit in the following way

In case of even parity: If a number of 1's is even then parity bit value is 0. If the number of 1's is odd then parity bit value is 1.
In case of odd parity: If a number of 1's is odd then parity bit value is 0. If a number of 1's is even then parity bit value is 1.

On receiving a frame, the receiver counts the number of 1's in it. In case of even parity check, if the count of 1's is even, the frame is accepted, otherwise, it is rejected. A similar rule is adopted for odd parity check.

The parity check is suitable for single bit error detection only.

Example: If the source wants to transmit data unit 1100111 using even parity to the destination. the source will have to pass through even parity generator.

The scheme makes the total number of 1's even that's why it's called even parity checking.

2. Checksum

In Checksum Error Detection scheme, the data is divided into k segments each of m bits.

At the sender's end the segments are added using 1's compliment arithmetic to get the sum. The sum is complemented to get the checksum.

The checksum segment is sent along with the data segments to the receiver.

At the receiver's end all received segments (included checksum) are added using 1's complement arithmetic to get the sum. The sum is complemented again.

If the result is 0, the received data is accepted otherwise discarded( rejected).

3. CRC

CRC stands for Cyclic redundancy Check. Unlike checksum scheme, which is based on addition, CRC is based on binary division.

In CRC, a sequence of redundant bits, are appended to the end of the data unit so that the resulting data unit becomes exactly divisible by a second, predetermined binary number.

At the destination, the incoming data unit is divided by then same number. If at this step there is no reminder, the data unit is assumed to be correct and is therefore accepted.

A reminder indicates that the data unit has been changed in transit and therefore must be rejected.

Example : Original Message - 1010000 and

Generator polynomial -x^3 +1 (1.x^3+ 0.x^2+0.X^1+1.x^0)

According to polynomial the CRC Generator will be 1001.

If CRC generator is of n bits then append (n-1) zeros in the end of original message.

4. LRC

LRC stands for Longitudinal Redundancy Check. It is also called two dimensional parity check.In this method , data which the user wants to send is organized in the form of rows and columns.In order to detect an error, a redundant bit is added to the whole block and this block is sent to the receiver along with the data.

At the receiver's end these are compared with the parity bits calculated on the received data.After checking data for errors, receiver accepts the data and discards the redundant row of bits.

Example : If a block of 32 bits is to be transmitted, it is divided into matrix of four rows and eight columns.

In this matrix of bits, a parity bit (odd or even) is calculated for each column. It means 32 bits data plus 8 redundant bits are transmitted to the receiver. Whenever data reaches at the destination, receiver uses LRC to detect an error in data.

Advantage : LRC is used to detect burst errors.

Example : Suppose 32 bit data plus LRC that was being transmitted is hit by burst error of length 5 and some bits are corrupted.

The LRC received by the destination does not match with newly corrupted LRC. The destination comes to know that the data is erroneous,so it discards the data.

Note : The main problem with LRC is that,if two bits in one data units are damaged and two bits in exactly the same position in another data unit are also damaged, then the LRC will not able to detect the error.

Error's and type of Error's At Data Link Layer

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When data is transmitted from one device to another device, the system does not guarantee whether the data received by the device is identical to the data transmitted by another device. Data Link layer uses Error control techniques to ensure that frames i.e, bit streams of data, are transmitted from the source to destination with a certain extent of accuracy.

Error

When bits are transmitted over the computer network, they are subject to get corrupted due to interference and network problems. The corrupted bits leads spurious data being received by the destination are called "Errors".

Errors are the condition when the receiver's information does not match with the sender's information. During transmission, digital signals suffer from noise that can introduce errors in the binary bits travelling from sender to receiver. That means a 0 bit change to 1 or 1 bit may be change to 0.

Types of Errors

Errors can be of 3 types namely Single Bit Error, Multiple Bit Error and Burst Error.

1. Single Bit Error: If in the received frame, only one bit has been corrupted, means either changed from 0 to 1 or from 1 to 0 then this type of error is called Single Bit Error.

2. Multiple Bit Error: If in the received frame , more than one bits are corrupted then this type of error is called Multiple Bit Error.

3. Burst Error: If in the received frame, more than one consecutive bits are corrupted then this type of error is called Burst Error.

The duration of noise in Burst Error is more than the duration of noise in Single-Bit Error.

LAN VS WLAN

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A network consist of two or more computers that are linked in order to share all form of resources including communication.

Both LAN and WLAN networks are interrelated and share moreover conman characteristics.

LAN

LAN stands for Local Area Network.LAN connections include both wired and wireless communication.

LAN network is a collection of computers or other such devices in a particular location that are connected together by communication elements or network elements.

LAN is free from external attacks like interruption of signals, cyber criminals attacks etc.So it is more secure.

LAN is not so much popular but less expensive.

Wired LAN needs physical access like connecting the wires to the switches or routers.

In LAN devices are connected locally with Ethernet cable.

It may or may not vary with external factors like environment and quality of cables.

Example : Computers connected in a college or any organization.

WLAN

WLAN stands for Wireless Local Area Network. WLAN connections are completely wireless.

WLAN network is a collection of computers or other such devices in a particular location that are connected together wirelessly by communication elements or network elements.

WLAN is vulnerable to external attack.So it is less secure.

WLAN is popular but more expensive.

WLAN works on connecting wires to the switches and routers are neglected.

Ethernet cable is not necessary in WLAN.

It varies due to external factors. Most of the external factors effect the signal transmission.

Example : Laptops, Phones, Tablets are connected to a wireless router or hotspot.

TCP/IP Model in Computer Network

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TCP/IP Model

The TCP/IP model was developed prior to the OSI model.The TCP/IP model is not exactly similar to the OSI model.It was designed and developed by Department of Defense in 1960. and is based on the standard protocols.

It stands for Transmission Control Protocol/Internet Protocol. TCP/IP model helps you to determine how a specific computer should be connected to the internet and how data should be transmitted between them.

The functionality of the TCP/IP model is divided into four layers, and each includes specific protocols.All these four TCP/IP layers work collaboratively to transmit the data from one layer to another.The layers are :-

1. Process/ Application layer

2. Host to Host/ Transport layer

3. Internet layer

4. Network Access/Link layer

Network Access Layer

A network Access layer is the lowest layer of the TCP/IP model. This layer corresponds to the combination of Data Link layer and Physical layer of the OSI model.

It defines how the data should be sent physically through the network.The functions carried out by this layer are encapsulating the IP datagram into frames transmitted by the network and mapping of IP addresses into physical addresses.

Internet Layer

An internet layer is the second layer of the TCP/IP model.An internet layer is also known as the network layer. This layers parallels the functions of OSI network layer.

The main responsibility of the internet layer is to send the packets from any network, and they arrive at the destination irrespective of the route they take.

It defines the protocols which are responsible for logical transmission of data over the entire network.The main protocols at this layer are-

IP : It stands for Internet Protocol. It is responsible for delivering packets from source Host to destination Host by looking at the IP addresses in the packet headers.

IP has two versions IPV4 and IPV6.

ARP : It stands for Address Resolution Protocol. ARP is a network layer protocol which is used to find the physical address from the IP address. ARP has several types like Reverse ARP, Proxy ARP, Inverse ARP etc.

ICMP : It stands for Internet Control Message Protocol.It is a mechanism used by the hosts or routers to send notifications regarding datagram problems back to the sender.

A datagram travels from router-to-router until it reaches its destination. If a router is unable to route the data because of some unusual conditions such as disabled links, a device is on fire or network congestion, then the ICMP protocol is used to inform the sender that the datagram is undeliverable.

The core responsibility of the ICMP protocol is to report the problems, not correct them. ICMP can send the messages only to the source, but not to the intermediate routers because the IP datagram carries the addresses of the source and destination but not of the router that it is passed to.

Transport Layer

This layer is analogous to the Transport layer of the OSI layer. It is also called The Host to Host Layer. IT is responsible for end to end communication and error free delivery of data.The transport layer is responsible for the reliability, flow control, and correction of data which is being sent over the network.

The two main protocols are presenting in this layer are :-

Transmission Control Protocol

TCP is a reliable protocol as it detects the error and retransmits the damaged frames.Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed.

At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original message.

At the receiving end, TCP collects all the segments and reorders them based on sequence numbers.

User Datagram Protocol

It provides connectionless service and end-to-end delivery of transmission.It is an unreliable protocol as it discovers the errors but not specify the error.

User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged.

Application Layer

An Application layer is the topmost layer in the TCP/IP model. This layer performs the functions of top three layers of the OSI model (Application, Presentation and Session layer) .

This layer allows the user to interact with the application.When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport layer.There is an ambiguity occurs in the application layer. Every application cannot be placed inside the application layer except those who interact with the communication system.

For example: Text editor cannot be considered in application layer while web browser using HTTP protocol to interact with the network where HTTP protocol is an application layer protocol.

Some of the protocols used in this layer are :-

HTTP: HTTP stands for Hypertext Transfer Protocol. This protocol allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio, video. It is known as a Hypertext Transfer Protocol as it has the efficiency to use in a hypertext environment where there are rapid jumps from one document to another.

SMTP: SMTP stands for Simple Mail Transfer Protocol. The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is used to send the data to another e-mail address. It is a combination of HTTP with SSL(Secure Socket layer).

DNS: DNS stands for Domain Name System. An IP address is used to identify the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. Therefore, the system that maps the name to the address is known as Domain Name System.

TELNET: Telnet stands for Teletype Network.It establishes the connection between the local computer and remote computer in such a way that the local terminal appears to be a terminal at the remote system.

FTP: FTP stands for File Transfer Protocol. FTP is a standard internet protocol used for transmitting the files from one computer to another computer.

ISO- OSI Model

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OSI Model

OSI stands for Open System Interconnection. It has been developed by "International Organization of Standardization", in the year 1984.

It is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer.

It is a 7 layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one computer to another across the globe. OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.

The OSI model is divided into two types of layers: upper layers and lower layers.

The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications.

An upper layer refers to the layer just above another layer.The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.

There are the seven OSI layers. Each layer has different functions. A list of seven layers are given below:

Physical Layer
Data-Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

1. Physical Layer

The main functionality of the physical layer is to transmit the individual bits from one node to another node.It is the lowest layer of the OSI model.It establishes, maintains and deactivates the physical connection.

Hub, Repeater, Modem, Cables are physical layer devices. IT also defines the transmission rate.

Functions of a Physical layer

Line configuration : It defines the way how two or more devices can be connected physically.

Data Transmission : It defines the transmission mode whether it is simplex, half-duplex or full-duplex mode between the two devices on the network.

Topology : It defines the way how network devices are arranged.

Signals : It determines the type of the signal used for transmitting the information.

2. Data Link Layer

This layer is responsible for the error-free transfer of data frames. The main function of this layer is to make sure data transfer is error-free from one node to another.

It defines the format of the data on the network.It provides a reliable and efficient communication between two or more devices.It is mainly responsible for the unique identification of each device that resides on a local network.

When a packet is arrives in a network, it's responsibility of Data Link Layer to transmit it to the Host using it's MAC address.

DLL is divided into two sub layers :

Logical Link Control Layer

It is responsible for transferring the packets to the Network layer of the receiver that is receiving.It identifies the address of the network layer protocol from the header.

It also provides flow control.

Media Access Control Layer

A Media access control layer is a link between the Logical Link Control layer and the network's physical layer.It is used for transferring the packets over the network.

Functions of the Data-link layer

Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and source address.

Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is transmitted to the destination address mentioned in the header.
Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with higher processing speed does not exceed the receiving station, with lower processing speed.
Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occur, then the receiver sends the acknowledgment for the re transmission of the corrupted frames.
Access Control: When two or more devices are connected to the same communication channel, then the data link layer protocols are used to determine which device has control over the link at a given time.

3. Network Layer

Network layer works for the transmission of the data from one host to another located in different network.It also take care of packet routing means selection of the shortest path to transmit the packet, from the numbers of route available.

The Data link layer is responsible for routing and forwarding the packets.The sender and receiver IP address are placed in the header by the network layer.

Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an inter network.

The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6.

Functions of Network Layer

Internetworking: An internetworking is the main responsibility of the network layer. It provides a logical connection between different devices.
Addressing: A Network layer adds the source and destination address to the header of the frame. Addressing is used to identify the device on the internet.
Routing: Routing is the major component of the network layer, and it determines the best optimal path out of the multiple paths from source to the destination.
Packetizing: A Network Layer receives the packets from the upper layer and converts them into packets. This process is known as Packetizing. It is achieved by internet protocol (IP).

4. Transport Layer

The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no duplication of data.The main responsibility of the transport layer is to transfer the data completely.

It receives the data from the upper layer and converts them into smaller units known as segments.It is responsible to end to end delivery of the complete message.

The transport layer also provides the acknowledgement of the successful data transmission and re transmits the data if an error is found.

The two protocols are used in this layer are:

Transmission Control Protocol

It is a standard protocol that allows the systems to communicate over the internet.

When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end.

User Datagram Protocol

User Datagram Protocol is a transport layer protocol.It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable.

Functions of Transport Layer

Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When the message has arrived at the destination, then the transport layer reassembles the message based on their sequence numbers.

Connection control: Transport layer provides two services Connection-oriented service and connectionless service. A connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the destination. A connection-oriented service makes a connection with the transport layer at the destination machine before delivering the packets. In connection-oriented service, all the packets travel in the single route.

Flow control: The transport layer also responsible for flow control but it is performed end-to-end rather than across a single link.

Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than across the single link. The sender transport layer ensures that message reach at the destination without any error.

5. Session Layer

This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security. the session layer allows two systems to start communication with each other in half-duplex and full-duplex mode.

Functions of Session layer

Session Establishment, Maintenance and Termination : The session layer allows the two processes to establish, use and termination a connection.

Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is known as Synchronization and recovery.

6. Presentation Layer

A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems.

It acts as a data translator for a network.This layer is a part of the operating system that converts the data from one presentation format to another format.

The Presentation layer is also known as the syntax layer.

Functions of Presentation layer

Translation: It converts the data from sender-dependent format into a common format and changes the common format into receiver-dependent format at the receiving end.
Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted information into another form and sends the resulting message over the network.
Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted. Data compression is very important in multimedia such as text, audio, video.

7. Application Layer

An application layer is not an application, but it performs the application layer functions.These application produce the data, which has to be transferred over the network.

This layer also serves as a window for the application services to access the network and for displaying the receiving information to the user.

Functions of Application layer

File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer, to retrieve the files from a computer and to manage the files in a remote computer.

Mail services: An application layer provides the facility for email forwarding and storage.

Note : OSI Model acts as a reference model and is not implemented in the internet because of it's late invention. Current model being used is the TCP/IP model.

Transmission Media

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Transmission Media

In data communication terminology transmission medium is physical path between the transmitter and the receiver. It is the channel through which data is sent from one place to another.

Transmission media is a communication channel that carries the information from the sender to the receiver. Data is transmitted through the electromagnetic signals.

Types of Transmission Media

there are two types of transmission media which are as follows:

Guided Media
Unguided Media

1. Guided Transmission Media

It is defined as the physical medium through which the signals are transmitted.It is also referred to as wired or bounded transmission media. Signals being transmitted are directed and confined in a narrow pathway by using physical links.

They are secure and and used for comparatively shorter distances.

There are various examples of guided media. Some of these are are as follows:

Twisted pair

Twisted pair is a physical media made up of a pair of cables twisted with each other. A twisted pair cable is cheap as compared to other transmission media. Installation of the twisted pair cable is easy, and it is a lightweight cable. The frequency range for twisted pair cable is from 0 to 3.5KHz.

A twisted pair consists of two insulated copper wires arranged in a regular spiral pattern.The degree of reduction in noise interference is determined by the number of turns per foot. Increasing the number of turns per foot decreases noise interference.

Coaxial Cable

Coaxial cable is very commonly used transmission media, for example, TV wire is usually a coaxial cable.The name of the cable is coaxial as it contains two conductors parallel to each other.

It has a higher frequency as compared to Twisted pair cable.The inner conductor of the coaxial cable is made up of copper, and the outer conductor is made up of copper mesh. The middle core is made up of non-conductive cover that separates the inner conductor from the outer conductor.

The middle core is responsible for the data transferring whereas the copper mesh prevents from the EMI(Electromagnetic interference).

Optical Fibre Cable

Fibre optic cable is a cable that uses electrical signals for communication. Fibre optic is a cable that holds the optical fibres coated in plastic that are used to send the data by pulses of light.The plastic coating protects the optical fibres from heat, cold, electromagnetic interference from other types of wiring. Fibre optics provide faster data transmission than copper wires.

2. Unguided Transmission Media

An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as wireless transmission or unbounded transmission media.

In unguided media, air is the media through which the electromagnetic energy can flow easily.The signals is broadcasted through air.

They are less secure and used for larger distance.

There are 3 types of signals transmitted through unguided media.

Radio waves

Radio waves are the electromagnetic waves that are transmitted in all the directions of free space.Radio waves are imnidirectional, i.e., the signals are propagated in all the directions.The range in frequencies of radio waves is from 3Khz to 1 khz.

In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by the sending antenna can be received by any receiving antenna.

An example of the radio wave is FM radio.

Infrared

An infrared transmission is a wireless technology used for communication over short ranges.The frequency of the infrared in the range from 300 GHz to 400 THz. It is used for short-range communication such as data transfer between two cell phones, TV remote operation, data transfer between a computer and cell phone resides in the same closed area.

It supports high bandwidth, and hence the data rate will be very high.An infrared communication provides better security with minimum interference.Infrared communication is unreliable outside the building because the sun rays will interfere with the infrared waves.

Microwaves

The microwave is another type of electromagnetic waves that have a frequency range of 1 GHz to 300 GHz. The microwave is unidirectional.

In this transmission, whenever the signals are transmitted through an antenna, the signals can make narrow to focus to a particular point. And in this transmission, there is a requirement of proper alignment of sending antenna and receiving antenna.

It supports the bandwidth from 1 to 10 Mbps. Microwave transmission is cheaper than using cables.

Microwaves are of two types:

Terrestrial microwave
Satellite microwave communication.

Network Devices in Computer Network

2021-11-13T14:50:00.000+05:30

Network Device

Networking devices or networking hardware are physical devices that are required for communication and interconnection between hardware on a computer network.

Hardware devices that are used to connect computers, printers, fax machines and other electronic devices to a network are called network devices. These devices transfer data in a fast, secure and correct way over same or different networks.

Network devices may be inter-network or intra-network. Some devices are installed on the device, like NIC card or RJ45 connector, whereas some are part of network, like router, switch, etc. Let us explore some of these devices in greater detail.

Router

A router is a network layer hardware device that transmits data from one LAN to another if both networks support the same set of protocols. A router is a device like a switch that routes data packets based on their IP address.It receives its data in the form of packets, which are data frames with their destination address added.

A router reads its routing table to decide the best available route the packet can take to reach its destination quickly and accurately. The routing table may be of these two types −

Static − In a static routing table the routes are fed manually. So it is suitable only for very small networks that have maximum two to three routers.

Dynamic − In a dynamic routing table, the router communicates with other routers through protocols to determine which routes are free. This is suited for larger networks where manual feeding may not be feasible due to large number of routers.

Switch

Switch is a network device that connects other devices to Ethernet networks through twisted pair cables. It uses packet switching technique to receive, store and forward data packets on the network. The switch maintains a list of network addresses of all the devices connected to it.

On receiving a packet it checks the destination address and transmits the packet to the correct port.The switch can perform error checking before forwarding data, which makes it very efficient as it does not forward frames that have errors and forward good packets selectively to the correct port only.The data is transmitted in full duplex mode.

Data transmission speed in switches can be double that of other network devices like hubs used for networking.This is because switch shares its maximum speed with all the devices connected to it.This helps in maintaining network speed even during high traffic. In fact, higher data speeds are achieved on networks through use of multiple switches.

Gateway

Gateway is a network device used to connect two or more dissimilar networks. In networking parlance, networks that use different protocols are dissimilar networks.

A gateway, as the name suggests, is a passage to connect two networks together that may work upon different networking module.They work basically work as an messenger agents that take data from one system, interpret it, and transfer it to another system.

Gateway uses packet switching technique to transmit data from one network to another. In this way it is similar to a router, the only difference being router can transmit data only over networks that use same protocols.

Hub

Hubs connect multiple computer networking devices together. A hub connects multiple wires coming from different branches, for example the connector in star topology which connects different stations. A hub is the simplest in the family of network connecting devices because it connects LAN components with identical protocols.

Hubs do not perform packet filtering or addressing functions; they just send data packets to all connected devices. Also they do not have intelligence to find out the best path for data packets which leads to inefficiencies and wastage. Hub is an broadcasting device that design to connect different computer with each other.

Bridge

Bridges are used to connect two or more hosts or network segments together. The basic role of bridges in network architecture is storing and forwarding frames between the different segments that the bridge connects. They use hardware MAC (Media Access Control) addresses for transferring frames.By looking at the MAC address of the devices connected to each segment, bridges can forward the data or block it from crossing.

Bridges work only at the Physical and Data Link layers of the OSI model. It is a two port device (one for input and one for output).

It is also used for interconnecting two LAN's working on the same protocol.However, bridges filter incoming data packets, known as frames, for addresses before they are forwarded. As it filters the data packets, the bridge makes no modifications to the format or content of the incoming data. The bridge filters and forwards frames on the network with the help of a dynamic bridge table. The bridge table, which is initially empty, maintains the LAN addresses for each computer in the LAN and the addresses of each bridge interface that connects the LAN to other LAN's.

Repeater

A repeater operates at the physical layer. It is job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network.

Repeaters do not amplify the signal when the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength.

Computer network and Types of Computer network

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Computer Network

A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications.

A computer network can be categorized by their size. A computer network is mainly of four types:

LAN(Local Area Network)
PAN(Personal Area Network)
MAN(Metropolitan Area Network)
WAN(Wide Area Network)

LAN(Local Area Network)

Local Area Network is a group of computers connected to each other in a small area such as building, office (Limited to few kilometres of area.)

LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc.

It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and Ethernet cables.

The data is transferred at an extremely faster rate in Local Area Network.Local Area Network provides higher security.

PAN(Personal Area Network)

Personal Area Network is a network arranged within an individual person, typically within a range of 10 meters.Personal Area Network is used for connecting the computer devices of personal use is known as Personal Area Network.

Thomas Zimmerman was the first research scientist to bring the idea of the Personal Area Network.Personal Area Network covers an area of 30 feet.

Personal computer devices that are used to develop the personal area network are the laptop, mobile phones, media player and play stations.

There are two types of personal area network.

1. Wired Personal Area Network

2. Wireless Personal Area Network

Wireless Personal Area Network: Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network.

Wired Personal Area Network: Wired Personal Area Network is created by using the USB.

MAN(Metropolitan Area Network)

A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network.Government agencies use MAN to connect to the citizens and private industries.

In MAN, various LAN's are connected to each other through a telephone exchange line.

The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL, etc.

It has a higher range than Local Area Network(LAN).

MAN is used in communication between the banks in the city. It can be used in any organization to connect all the different branches of a city.

WAN(Wide Area Network)

A Wide Area Network is a network that extends over a large geographical area such as states or countries.A Wide Area Network is quite bigger network than the LAN.

A Wide Area Network is not limited to a single location, but it spans over a large geographical area through a telephone line, fiber optic cable or satellite links.

The internet is one of the biggest WAN in the world.

A Wide Area Network is widely used in the field of Business, government, and education.

Advantages Of Wide Area Network:

Following are the advantages of the Wide Area Network:

Geographical area: A Wide Area Network provides a large geographical area. Suppose if the branch of our office is in a different city then we can connect with them through WAN. The internet provides a leased line through which we can connect with another branch.

Centralized data: In case of WAN network, data is centralized. Therefore, we do not need to buy the emails, files or back up servers.

Get updated files: Software companies work on the live server. Therefore, the programmers get the updated files within seconds.

Exchange messages: In a WAN network, messages are transmitted fast. The web application like Facebook, Whatsapp, Skype allows you to communicate with friends.

Sharing of software and resources: In WAN network, we can share the software and other resources like a hard drive, RAM.

Global business: We can do the business over the internet globally.

Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

Security issue: A WAN network has more security issues as compared to LAN and MAN network as all the technologies are combined together that creates the security problem.

Needs Firewall & antivirus software: The data is transferred on the internet which can be changed or hacked by the hackers, so the firewall needs to be used. Some people can inject the virus in our system so antivirus is needed to protect from such a virus.

High Setup cost: An installation cost of the WAN network is high as it involves the purchasing of routers, switches.

Troubleshooting problems: It covers a large area so fixing the problem is difficult.

Topology in Computer Network

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Topology

Topology defines the structure of the network of how all components are interconnected to each other.There are two types of topology: Physical and Logical. Physical topology is the geometric representation of all the node in a network.

Types of Topology

There are various type of topology which are given below :

1. Bus Topology

The bus topology is designed in such a way that tell the stations are connected through a single cable known as a backbone cable.Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.

In case of Bus topology, all devices share single communication line or cable.Bus topology may have problem while multiple hosts sending data at the same time.

It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning.

The configuration of a bus topology is quite simpler as compared to other typologies. The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations.

2. Ring Topology

In ring topology, each host machine connects to exactly two other machines, creating a circular network structure. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable.

The data flow is one direction means it is unidirectional.The data flow in a clockwise direction. The most conman access method of ring topology is token passing.

Failure of any host results in failure of the whole ring.Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring.

3. Star Topology

Star topology is an arrangement of the network in which every node is connected to the central device like hub, switch or router or a central computer.

The central computer is known as a server as a server, and the peripheral devices attached to the server are known as clients.Coaxial cable or RJ-45 cables are used to connect the computer.

As in Bus topology, hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts, takes place through only the hub.Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple.

4. Tree Topology

Tree topology combines the characteristics of bus topology and star topology.A tree topology is a type of structure in which all the computers are connected with each other in hierarchical fashion so it is also know as Hierarchical Topology.

The top most node in tree topology is know as root node, and all the other nodes are the descendants of the root node. There is only one path exist between two nodes for the data transmission. Thus it forms a parent-child hierarchy.

This topology divides the network in to multiple levels/layers of network. Mainly in LAN's, a network is bifurcated into three types of network devices. The lowermost is access-layer where computers are attached. The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer. The highest layer is known as core layer, and is central point of the network, i.e. root of the tree from which all nodes fork.

All neighboring hosts have point-to-point connection between them.Similar to the Bus topology, if the root goes down, then the entire network suffers even.though it is not the single point of failure. Every connection serves as point of failure, failing of which divides the network into unreachable segment.

5. Mesh Topology

Mesh topology is an arrangement of the network in which computers are interconnected with each other through various redundant connections. there are multiple paths from one computer to another computer. It does not contain the switch, hub or any central computer which act as a central point of communication.The internet is the example of Mesh topology.

Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to-point links. Mesh technology comes into two types:

Full Mesh: All hosts have a point-to-point connection to every other host in the network. Thus for every new host n(n-1)/2 connections are required. It provides the most reliable network structure among all network topologies.

Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all.

6. Hybrid Topology

A network structure whose design contains more than one topology is said to be hybrid topology. Hybrid topology inherits merits and demerits of all the incorporating topologies.

When two or more different topologies are combined together is termed as Hybrid topology.The above picture represents an arbitrarily hybrid topology. The combining topologies may contain attributes of Star, Ring,and Bus topologies. Internet is the best example of largest Hybrid topology.

Data Flow

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Devices communicate with each other by sending and receiving data. The data can flow between the two devices in the following ways.

1. Simplex Mode

In simplex mode, communication is unidirectional. Only one of the devices sends the data and the other one only receives the data.

A CPU send data while a monitor only receive data.

2. Half Duplex Mode

In half duplex mode both the stations can transmit as well as receive but not at the same time. When one device is sending other can only receive and vice-versa.

Example : walkie-talkie

3. Full-Duplex Mode

In the full duplex mode, both stations can transmit and recieve at the same time.

Example : Mobile phones

Data Representation

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Data is a collection of row facts which is processed to deduce information. There may be different forms in which data may be presented. Some of the forms of data used in communication are as follows-

1. Text : Text includes combination of alphabets in small case as well as upper case. It is stored as a pattern of bits.

2. Numbers : Numbers include combinations of digits from 0 to 9. It is stored as a pattern of bits.

3. Images : A image is a worth of thousand words. In computers images are digitally stored. A pixel is the smallest element of an image. A picture or an image is a matrix of pixel elements.

The pixels are represented in the form of bits. depending upon the type of an image(Black & White or color) each pixel would require different numbers of bits to represent the value of a pixel.

4. Audio : Data can also be in the form of sound which can be recorded and broadcasted. Audio data is continuous not discrete. Example what we hear on the radio is a source of data or information.

5. Video : video refers to broadcasting of data in the form of picture or movie.

Data Communication in Computer Network

2021-10-23T10:45:00.004+05:30

Data Communication

The term data communication comprises two words : Data and Communication.Data can be any text, image, audio, video and any multimedia files. and the communication is an act of sending and receiving data.

Thus data communication refers to the exchange of the data between two or more networked or connected devices. example of such devices include personal computers, mobile phones, laptops etc.

Data communication refers to the exchange of data between a source and a receiver via form of transmission medium such as wired cable.

The data communication is said to be local if communicating devices are in the same building or a similarly restricted geographical area.

The device that transmits the data is known as source and the device that receives the transmitted data is known as receiver.

Components of data communication

A communication system has following components :-

1. Sender : A sender is a device which is capable of sending data over a network. It can be a computer, mobile phone, laptop, smart watch etc.

2. Receiver : It is a destination where finally message sent by source has arrived. It is a device that receives message same as sender. receiver can also be in form of a computer, telephone, mobile , workstation etc.

3. Message : It is the data or information that needs to be exchanged between the sender and the receiver. Message can be in the form of text, image, audio, video, multimedia files etc.

4. Transmission Medium : It is the channel or physical path through which the message is carried from sender to the receiver. The medium can be wired like twisted pair cable, fiber-optic cable etc. or wireless like laser, radio waves and microwaves.

5. Protocol : It is a set of rules that govern the communication between the devices. Both sender and receiver follow same protocols to communicate with each other.

To govern data communication, various set of rules had been already designed by the designers of the communication system, which represent a kind of agreement between communicating devices. These are defines as protocol.

Example of a data communication system is sending an email. The user which send email act as sender, message is data which user wants to send, receiver is one whom user wants to send a message, there are many protocols involved in this entire process, like SMTP(Simple Mail Transfer Protocol), both sender and receiver must have an internet connection which uses a wireless medium to send and receive email.

Characteristics of Data Communication

The effectiveness depends on four fundamental characteristics of data communication.

1. Delivery : The data must be deliver in correct order with correct destination.

2. Accuracy : The data must be deliver accurately means no change in the content of message sent by the sender during the transmission.

3. Timeliness : The data must be deliver in a timely manner late delivered data useless.

4. Jitter : It is the uneven delay in the packet arrival time that cause uneven quality. Jitter refers to the variation in the packet arrival time.

Example : Let us assume that video packets are sent every 30 m.s If some of the packets arrive with 30 ms and others with 40 ms delay, an uneven quality in the video id result.