Network Programming :-

Network Programming is to write a program that communicates with other programs across a computer network.

Before we go to write a server/client program first we will understand the concept of Server, Client,       IPAddress, Port, Protocol and Socket.

Server

·         A server is a program that awaits and fulfills requests from client programs

·         A server is an entity which is a provider of information.

Client

·         The client makes a service request from the server, which fulfills the request.

·         A client is an entity which is a seeker of information.

IP address

An IP address is assigned to each device on a network for the purpose of identification.
For example:

In Fig 1.1 There are four computers in a network. If device ‘A’ wants to communicate with device ‘B’ it will connect with the IP address “192.168.2.1” because this IP address is the address of ‘B’ computer

Port

The Port value identifies a particular application on a device.

(The IP address will Identify a particular device on a network but that device could also be running multiple applications, So with the help of IP address the data will arrive at the specific device, but if no port number is assigned the data will be lost because the computer doesn’t know to which application data has to be moved)

For Example:

In Fig 2.2, On device ‘B’ there are two applications running ‘Alpha’ with port number 5000 and ‘Beta’ with port number 8000. Now if application ‘Beep’ on device ‘A’ wants to send data to device ‘B’ to application ‘Alpha’. It will send the data to IP address “192.168.2.1” with 5000 port number assigned. If port number is not assigned the data cannot reach to application ‘Alpha’

Similarly if we want to send data to device ‘B’ to application ‘Beta’ we have to define the IP address “192.168.2.1” and port number 8000.

 

Socket

A socket is one endpoint of a two way communication between two Programs running on a network

(It is a software component not hardware)

When the socket is created (we will learn how to create a socket soon). It should be bound to port number and IP address once it is bound it can be used to send and receive data.

Below explanation of sockets and protocols is not necessary at this point you can skip this part if you want to

There are three types of socket

(1)       Stream Socket.

(2)       Data gram Socket.

(3)       Raw Socket.

Stream Socket is based on TCP/IP protocol.                                                        (See below for protocols)

Data gram Socket is based on UDP protocol.

Note:  We will use a Stream socket in our Server/Client Program which is based on TCP/IP protocol which guarantee the delivery of data

Protocols

(1)    TCP/IP protocol.

(2)    UDP protocol.

TCP/IP protocol ensures the delivery of message between two computers.

For example if computer A sends some message to computer B. The TCP/IP protocol would ensure that this message will reach at its destination computer B.  TCP/IP protocol would not let the message get lost on its way to computer B.

Real life example would be ‘E-mail’. When you send e mail to your friend it does reach to your friend’s inbox 100%.

UDP protocol does not guarantee the delivery of message between two computers.

For example if computer A sends some message to computer B. The UDP protocol cannot ensure that this message will reach at its destination B.

Real life example would be ‘Media Streaming’ where some message (packet) might get lost. That is why when you see any live TV show on media streaming you can get some scenes skipped.

Socket Programming

So this is how our Server/Client program is going to work

 
                                                                                                                                                                        The above diagram is like a flow chart of our socket program that we are going to make.

Creating Server…

In Fig 3.3 see the list of functions at server side only

(1)    socket()

(2)    bind()

(3)    listen ()

(4)    accept()

(5)    recv()

(6)    send()

(7)    close()

It means that we have to code our server program in the same sequence of steps as mention above

So when you are making a server program you simply have to remember these seven steps.

First step

First step is to create a socket.

Second step

In second step we use the bind() function to “bind”  this socket with IP address and port number (details of IP address and port number are listed above).

Third step

In third step we use the listen() function to  “Listen” for any incoming connection from client

Listening simply means that server is ready and looking for client .

                     

Fourth step

In Fourth step the server will wait until the connection request arrives from client, when the request arrives the server will accept the client connection request via accept() function.

To understand what ‘connection request’ means consider the real life example

If you want to use the facebook, you first have to connect the facebook by sending the connection request first, you send the connect ion request to  facebook by writing “www.facebook.com” in the URL. In this case you are client and facebook is ‘server’

Since we are still in the beginning of network programming, In our client /server program our client connects to server by assigning the IP address and port number of server.

(You will see in client program how the client connects to server)

Fifth step

In Fifth step the server will again wait to receive data from client via Receive() function

Sixth step

In sixth step the server will send data to client via send() function.

Seventh step

In Seventh step the connection with the client is closed via close() function.

That’s it, just implement these seven steps in your code and you have your server ready.

First add two namespaces in your server program.

(1)    using System.Net;

(2)    using System.Net.Sockets;

Here are the codes of Server program…

// Preparing IP address and Port number

IPAddress ipAddress = IPAddress.Parse(“192.168.1.1”);

IPEndPoint endPoint = new IPEndPoint(ipAddress, 8000);

// Creating a Socket -- First Step

Socket  serverSocket = new 
Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);

// Binding the socket with endpoint  which contains the IP address and port number – Second Step

serverSocket.Bind(endPoint);

// Server listens for connection from client – Third Step

serverSocket.Listen(10);

// Will accept the client connection request – Fourth Step

Socket  clientConnected = serverSocket.Accept();

 // Receive the data/message send by client – Fifth Step

 byte[] rcvdData = new byte[10];

 int size = clientConnected.Receive(rcvdData);

 string convertedData = Encoding.ASCII.GetString(rcvdData,0,size);

 Console.WriteLine(convertedData);

 // Send the data/message to client – Sixth Step

 Console.WriteLine("Enter Message...");

 string readData = Console.ReadLine();

 clientConnected.Send(ASCIIEncoding.ASCII.GetBytes(readData));

 // close the connection with client – Seventh Step

clientConnected.Close();

See server program follows the same sequence we have discussed in Fig 3.3

Now some explanation of codes..

Ø  IPAddress ipAddress = IPAddress.Parse(“192.168.1.1”);

The above code will assign the IP address. We have to put IP address of server. Assuming our server and client runs  on different compter,  We can also make server and client on the same computer in that case change the ip to “127.0.0.1”

Ø  IPEndPoint endPoint = new IPEndPoint(ipAddress, 8000);

The endpoint object contains the IP address and port number

Ø  Socket  serverSocket  = new   Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);

The above code will create a socket.

Now I will explain the details of the above code you can skip this part as it is not necessary to go into the details at this point .

We have discussed Stream and UDP socket above, In the below explanation I will show you how to create Stream socket and UDP socket.

Creating Stream Socket…

 Socket  streamSocket  = new   Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);

So Inorder to create a stream socket.

We have to specify  AdressFamily to ‘InterNetwork’.

We have to specify  SocketType to ‘Stream’.

We have to specify ProtocolType to ‘Tcp’.

Creating UDP Socket ….

Socket  udpSocket  = new   Socket(AddressFamily.InterNetwork,SocketType.Dgram,ProtocolType.Udp);

So Inorder to create a udp socket.

We have to specify AddressFamily to ‘InterNetwork’.

We have to specify SocketType to ‘Dgram’.

We have to specify ProtocolType to ‘UDP’.

That’s it by changing the  properties in code we can make either Stream or Udp socket.

Remember in our Server/client program we will only use the stream socket. Understanding of UDP socket is not necessary at this point. I am showing you to create UDP Socket here only because so that you can have better understanding of properties such as (AddressFamily, SocketType, ProtocolType) used in the code to create a socket.

Ø  serverSocket.Bind(endPoint);

The Bind() method will bind the IP address and port number to socket via endpoint.

                                                                                                                                                                      

Ø  serverSocket.Listen(10);

The server will starts to Listen for connection from clients.

I will explain in my next lecture that why we put the value’10’ in Listen function as for now just remember that  you  have to put value ‘10’ in Listen function

Ø  Socket clientConnected = socket.Accept();

Accept() will block the further execution of program untill there is any connection request made by client.. When the client is connected the accept method will accept its request and then the program will be able to execute the codes below the Access method.

Ø  byte[] rcvdData = new byte[10];

 int size = clientConnected.Receive(rcvdData);

 string convertedData = Encoding.ASCII.GetString(rcvdData,0,size);

 Console.WriteLine(convertedData);

The above first three lines of codes is used to receive data from client.

byte[] rcvdData = new byte[10];

We have to make Array of bytes in which the data/message is going to store sent by client. You can put any size of Array you want to but if the data/message sent by client is larger than the size of array you have defined then you will not receive wole message sent by client

int size = clientConnected.Receive(rcvdData);

Receive method will put client message in byte Array ‘rcvdData’. Receive method  also blocks the program like Accept() we have discussed above, the Receive method blocks the program utill it did not receive any data/message from client. Once it receive the data from client the further execution of program can take place

string convertedData = Encoding.ASCII.GetString(rcvdData,0,size);

Since the data we received is in bytes from so we need to convert  the data into string ‘Encoding.ASCII.GetString(rcvdData,0,size)’  will convert the bytes into string

Console.WriteLine(convertedData);

Console.WriteLine is simply printing the convertedData on screen which contains the client message.

Ø  Console.WriteLine("Enter Message...");

 string readData = Console.ReadLine();

 connectedClient.Send(ASCIIEncoding.ASCII.GetBytes(readData));

The sbove second and third line of code will send the data/message to client

Console.WriteLine("Enter Message...");

This will simpliy print the “Enter Message” on screen

string readData = Console.ReadLine();

Console.ReadLine()  also blocks the program like Accept() we have discussed above, it will wait untill we put any message in that and then that message is going to save in ‘readData’

connectedClient.Send(Encoding.ASCII.GetBytes(readData));

Inorder to send the data to client we have to convert our string data into Bytes

“Encoding.ASCII.GetBytes(readData)”  will do the job for us it will convert the readData into Bytes

Then the Send method will simply send the data to client.

That is all for the server program

Now heading towards the client …

Creating Client…

In Fig 3.3 see the list of functions at client side only

(1)    socket()

(2)    connect()

(3)    send()

(4)    recv()

(5)    close()

It means that we have to code our client program in the same sequence of steps as mention above.

 So when you are making a client program  you simply have to remember these five steps.

First step 

First step is to create a socket .                                          (Similarly as we have created socket in server)

Second step 

 Second  step is to Connect  that socket via connect() function. Through the connect() function you actually made connection request to server.

Third step

In third step the client will send data to server  via send() function.

Fourth step

In fourth step the client will wait to receive data from server  via Receive() function.

Fifth step

In Fifth step the connection with the server is closed via close() function.

That’s it just implement these five steps in your code and you have your client ready.

First add two namespaces in your client program.

(3)    using System.Net;

(4)    using System.Net.Sockets;

Here are the codes of Client program…

// Preparing IP address and Port number

IPAddress ipAddress = IPAddress.Parse(“192.168.1.1”);

IPEndPoint endPoint = new IPEndPoint(ipAddress, 8000);

// Creating a Socket

Socket  clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

// connecting it with the server

clientSocket.Connect(endPoint);

// Send the data/message to server

 Console.WriteLine("Enter Message:");

 string readData = Console.ReadLine();

 clientSocket.Send(ASCIIEncoding.ASCII.GetBytes(readData));

// Receive the data/message sent by server

 byte[] rcvdData = new byte[1];

 int size = clientSocket.Receive(rcvdData);

 string rcvdMsg = ASCIIEncoding.ASCII.GetString(rcvdData, 0, size);

 Console.WriteLine(rcvdMsg);

// close the connection with server

 clientSocket.Close();

Explanation of codes..

Ø  IPAddress ipAddress = IPAddress.Parse(“192.168.1.1”);

The above code will assign the IP address. Although this is a client program but we have to put IP address of server because the client will connect to server with the help of IP address of server.

Ø  IPEndPoint endPoint = new IPEndPoint(ipAddress, 8000);

The endpoint object contains the IP address and port numberAgain we have to assign port number of server application because with the help of port number client data will reah at specific application.

Ø  clientSocket.Connect(endPoint);

The Connect method will connect the client to server.

Remaining codes of client is same as of the server program.

This is our simple server/client application

I Hope it helps

Thankyou for reading