• A Network is a collection of devices that share a common communication protocol and connected with some communication medium.
• A protocol defines a set of rules to which all the communicating parties adhere to (agree).
• The java.net package was designed with a group of classes and interfaces which not only provide low level but also hight level communication details.
• java.net package provides support for the two common network protocols. i. TCP (Transmission Control Protocol) ii. UDP(User Datagram Protocol)
• The term network programming refers to writing programs, then execute across multiple devices, in which the devices are all connected to each other using a network.

Network Programming

   1. Socket Programming
   2. URL Processing

1. IP Address

• It is a logical address that can be changed. IP Address are 32-bit number (IPv4 format) often represented as a quad of four 8-bit numbers separated by periods. Eg : 192.168.0.1

2. Protocol

• It is a set of rules basically that is followed for communication. Eg: TCP, UDP, FTP, POP, SMTOP, HTTP, HTTPS

3. Port Number

• The port number is used to uniquely identify different applications. It acts as a communication end point between applications.
• The valid port number range from 1 - 65535.
• The ports upto 1023 are reserved for well known services and hence are well-known ports. Eg: 80 for HTTP, 21 for FTP, 22 for SSH

4. Socket

• A socket is a end point between two way communication.
• It defines a network connection as a Stream from which bytes can be read and similarly bytes can be sent.
• Java socket can be used to provide both connection-oriented (TCP) as well as connectionless (UDP).