This document provides an introduction to networking and internet concepts like protocols, TCP, UDP and client-server computing. It explains key classes in the java.net package used for network programming like InetAddress, Socket, ServerSocket, DatagramSocket, DatagramPacket, URL, URLConnection and ContentHandler. The classes help establish connections, send/receive data and interact with resources on the web. Common port numbers and their associated protocols are also listed. TCP establishes links between source and destination ports while UDP is connectionless and sends data in datagrams without delivery assurance.
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