Networking involves connecting computing devices together to share resources using a mix of hardware and software. Devices are uniquely identified on a network using IP addresses. There are several layers in the networking model including the physical, link, network, transport, and application layers. The application layer contains protocols like HTTP, FTP, and SMTP that are used by user programs. URLs contain the protocol, hostname, port, and filename to uniquely identify resources. Sockets provide connections between applications to allow data transfer using protocols like TCP and UDP.

1. Core Java
Debasish Pratihari
Networking:

Networking is the linking of two or more
computing devices together with a purpose of
sharing data and other resources.

Networks are built with a mix of computer
hardware and computer software.

In networking the communication language used
by computer devices is called protocol.

An IP address helps to uniquely identify a
device in the network.
Network Layers :
Application Layer
(HTTP, FTP,Telnet…)
Application Layer
(HTTP, FTP,Telnet…)
Transport Layer
( TCP, UDP )
Transport Layer
( TCP, UDP )
Network Layer
(IP,…)
Network Layer
(IP,…)
Link Layer
( Device driver,..)
(IP,…)
Link Layer
( Device driver,..)
(IP,…)
Physical Layer – Ethernet, wireless, etc…
Note :
 The OSI Model is
having seven layers.
 As a java
programmer you are
programming
Application
Layer.
IP Address :

An Internet Protocol (IP) address is a numerical
identification (logical address) that is assigned to
devices participating in a computer network.

It is a 32-bit number(4-octects)

Example :192.168.1.1

Note :
The IP address in IPv6
is 128 bit. However
IPv4 is still in use and
will be in use for some
more years.
When a computer is configured to use the same IP
address each time it powers up, this is known as a
Static IP address. In contrast, in situations when
the computer's IP address is assigned automatically,
it is known as a Dynamic IP address.
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2. Core Java
Port :
 Is a logical connection
Network.
Debasish Pratihari
end-point in the

Transport Layer protocols specify a source and
destination port number in their packet header.

A port number is a 16-bit unsigned integer(065,535).

A process associates with a particular port
(called binding) to send and receive data.

Port number 0- 1023 are knows as wellknown ports
Application Layer:

The Application Layer involves all the user
related programs like web browsers and ftp.

The application layer programs use various
protocols:
HTTP
FTP
Telnet
SMTP
Hyper Text Transfer Protocol
File Transfer Protocol
the telnet protocol provides for
console sessions.
Simple Mail Transport Protocol email.
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3. Core Java
Debasish Pratihari
URL:

Browsers obtain resources from the Web by
specifying the Web addresses, which are
referred to officially as Uniform Resource
Locators (URL).

Example :

URL components :
o Protocol identifier
o Resource Name

A general Format of URLs :
http://www.lakshyatraining.org/
Protocol_ID://Host_IP_address:Port/Filename#Target
Where
Protocol_ID
HTTP, FTP, etc
Host_IP_address Host name in either numerical IP or
hostname format
Port
default is 80
Filename
Target
Name of a hypertext web page or
other type of file. Default
index.htm[l]
optional reference address within a
Web page
Socket:


Sockets provide connections between applications
and allow streams of data to flow.
Java provides two kinds of sockets:
 Socket: provides a connection-oriented
protocol that behaves like telnet or ftp. The
connection remains active, even with no
communications occurring, until explicitly
broken.
 DatagramSocket:
o a connectionless protocol
o transfers datagram packets
o no fixed connection
o does not keep packets in order
o no guarantee a packet will arrive at its
destination
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Note :
 Socket uses
TCP/IP and
DatagramSocket
uses UDP protocol
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4. Core Java
Debasish Pratihari
URL Example :
25%
import java.net.*;
import java.io.*;
public class URLDemo
{
public static void main (String[] args) {
if (args.length !=1) {
System.out.println ("Error: missing the url argument");
System.exit (0);
}
}
try {
URL url = new URL (args[0]);
System.out.println ("Protocol = " + url.getProtocol ());
System.out.println ("Host = " + url.getHost ());
System.out.println ("File name = " + url.getFile ());
System.out.println ("Port = " + url.getPort ());
System.out.println ("Target = " + url.getRef ());
}
catch (MalformedURLException e) {
System.out.println ("Bad URL = " + args[0]);
}
}
MalformedURLException :


Each of the four URL constructors throws a
MalformedURLException if the arguments to
the constructor refer to a null or unknown
protocol.
you cna handle this exception by embedding
try/catch to your
try {
URL myURL = new URL(. . .)
} catch (MalformedURLException e) {
...
// exception handler code here
...
}
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5. Core Java
Debasish Pratihari
Using Socket:
 A socket is one endpoint of a two-way
communication link between two programs
running on the network.
 A socket is bound to a port number so that the
TCP layer can identify the application that data
is destined to be sent.
 Basic Steps :





Open a socket.
Open an input stream and output stream to
the socket.
Read from and write to the stream according
to the server's protocol.
Close the streams.
Close the socket.
Java Sockets for connection oriented
Communication:
 Socket types:
o ServerSocket
o Socket
 To create a ServerSoket:
ServerSocket ss=
new ServerSocket(port,quelength);
Where
Port
- port number
queuelength -Specifies the number of clients that can
wait for a connection and pressed by the server. If the queue is
full client connection refused.

To accept a connection request from the
client:
Socket con= ss.accept();

To get the input/output stream:
Con.getInputStream();
Con.getOutputStream();

To send and receive data:
BufferedWriter br=
new BufferedWriter(newInputStreamWriter(
con.getOutputStream());
BufferedReader br= new BufferedReader(new
InputStreamReader(con.getInputStream());
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6. Core Java
Debasish Pratihari
Example :
Objective – To get the server date using Stream
Socket
Server Program
FileName-DayServer.java
import java.net.*;
import java.io.*;
import java.util.*;
public class DayServer{
private ServerSocket ss;
public static void main(String args[]) throws
IOException{
DayServer ds = new DayServer();
for(;;)
ds.serve();
}
public DayServer() throws IOException{
ss= new ServerSocket(13,5);
}
public void serve() throws IOException{
Socket s = null;
s = ss.accept();
BufferedWriter out = new BufferedWriter( new
OutputStreamWriter(s.getOutputStream()));
out.write("Day & Time :"+ (new
Date()).toString());
out.close();
s.close();
}
}
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7. Core Java
Debasish Pratihari
Client Programs
FileName – DayClient.java
import java.net.*;
import java.io.*;
import java.util.*;
public class DayClient {
String Host;
Socket soc;
public DayClient(String phost) throws
IOException{
this.Host=phost;
}
public void getDate() throws IOException{
soc= new Socket(Host,13);
BufferedReader br = new BufferedReader(new
InputStreamReader(soc.getInputStream()));
System.out.println(br.readLine());
br.close();
soc.close();
}
public static void main(String args[]) throws
IOException{
DayClient dc= new DayClient(args[0]);
dc.getDate();
}
}
To Run (in single system):
 Compile both the programs.
 Run the Server program first.
 Open a new command window and run the client
as follows:
 Java DayClient localhost
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