Web Programming Essentials

Web Programming Course Resources

• Course materials include javatpoint.com, tutorialspoint.com, geeksforgeeks.org, w3schools.com, and a book by 이용규 on Web Programming

Lecture and Grading Information

• Lecture notes can be found in the KLAS 강의 자료실.
• The grade is determined by attendance (5%), Quizzes (20%), Assignments/Presentation (20%), Mid exam (25%), and Final exam (30%)

Web Programming Topics

• Network Concepts
• Internet and WWW
• HTML, CSS, and XML
• Java Concepts
• Client-side Web Programming: AJAX, JavaScript
• Database Concepts and JDBC
• Server-side Web Programming: PHP, Servlet, JSP

Computer Networks

• Computer networks involve computing devices connected to communicate and share resources
• A node is any device in the network that can send, receive or process data
• A bridge connects two similar networks
• A switch connects several similar networks
• A router connects two or more different networks
• A gateway translates communication between fundamentally different network architectures
• Connections can use physical wires/cables or be wireless
• Data can be transmitted in analog or digital form

Network Classification by Geographic Coverage

• A Local Area Network (LAN) is a small network for homes or offices
• A Metropolitan Area Network (MAN) covers a campus or city
• A Wide Area Network (WAN) operates at a state or country level
• The Internet is the ultimate WAN

Network Classification by Topology

• Ring topology: Nodes are connected in a closed loop
• Star topology: A central node controls all message traffic
• Bus topology: All nodes share a common line
• Modern Ethernet networks use a star topology with a switch at the center, though Ethernet was originally based on bus topology

Network Classification by Transmission Method

• Wired networks use physical cables like Ethernet and fiber optics for stable, high-speed communication
• Wireless networks use radio waves like Bluetooth, Wi-Fi, 4G/5G, microwaves, and infrared for flexibility and mobility

Wireless Network Types

• Bluetooth is optimized for short-range connectivity in devices like smartphones, headsets, keyboards, and mice
• Wi-Fi is designed for local area connectivity and Internet access through WAPs or Wi-Fi routers
• 4G/5G is designed for mobile communication, providing high-speed data and voice over long distances for smartphones and tablets

Network Classification by Message Switching Method

• Circuit switching establishes a dedicated route between sender and receiver, typical in telephone networks
• Packet switching sends data units to the receiver, without requiring a dedicated path

Characteristics of Packet Switching

• Data is stored and forwarded node by node until reaching its destination
• Messages are split into fixed-size packets individually routed and reassembled at the destination
• Routers direct packets between networks toward their destination
• Packet switching is used in the Internet, cloud computing, and LAN/MAN/WAN setups

Network Classification by Communication Model

• The client-server model involves client nodes requesting services and server nodes responding
• The World Wide Web is an example of client server-architecture
• Peer-to-peer (P2P) model: every node can request and respond to services
• In the P2P model, a node can act as either a client or a server
• P2P networks eliminate the need for a single server
• P2P networks are more difficult to administer and prone to security issues
• Blockchain is an example of a peer-to-peer that is cryptographically-secure and decentralized
• P2P is common in LANs, while MANs and WANs tend to use the Client-Server model due to scale

Internetworks

• LANs and WANs are rarely isolated and are typically connected to each other
• An internetwork is formed when two or more different networks connected
• For example, a company might have two offices each with its own LAN and then lease a WAN from a telephone to company connects them.
• Most notably is the Internet, composed of thousands of interconnected networks worldwide

Internet Structure

• Backbone networks owned by companies like AT&T use complex switching systems to carry internet traffic
• Provider networks use the services of the backbones for a fee.
• Customer networks are at the edge of the Internet and use its services

Internet Connection Technologies

• Wired connections use a phone modem, digital subscriber line, cable modem or fiber-optic cables
• Wireless connections use Wi-Fi, mobile networks (4G/5G), or satellite.

Protocols

• Protocols are a set of rules defining how data is formatted and processed on a network
• It serves as a common language for devices
• Open systems use standardized, publicly available protocols and interfaces for interoperability, scalability, and vendor-independent communication.

OSI Reference Model

• The Open Systems Interconnection (OSI) reference model, standardizes network communication into seven layers, allowing interoperability across technologies
• Each layer handles a specific aspect of network communication
• Specific list of these layers are physical, data link, network, transport, session, presentation, and application
• The highest layer addresses application program-specific issues
• The lowest layer addresses electrical and mechanical issues of the physical transmission medium
• The transport layer handles end-to-end communication, error recovery, and flow control
• The network layer handles the routing and addressing of packets

TCP/IP

• A suite of protocols used to interconnect network devices on the internet
• The Application layer contains protocols and standards that support specific applications and services.
• The Transport layer ensures end-to-end communication between devices across a network

Transport Layer Protocols

• TCP is a connection-based protocol, making it more reliable but slower since it breaks messages into packets and reassembles them while addressing errors
• UDP is a connectionless protocol, making it less reliable but faster because it breaks messages into datagrams without guaranteeing order, delivery, or error correction

Network and Interface Layers

• The network layer handles addressing and routing of data packets between different networks
• The Internet Protocol (IP) is the network protocol and deals the routing of packets
• The network interface layer deals with the physical connection between devices on the same network
• It is referred to as TCP/IP due to the heavy reliance on TCP

How TCP/IP Works

• A message starts in the application layer, which constructs the message with an address
• The message then passes to the transport and network layers for transmission preparation
• Finally the message is transmitted by the link layer
• At each point, the network later determines which direction the message should be forwarded on

High Level Protocols Built on TCP/IP

• File Transfer Protocol (FTP) transfers files between computers
• Hypertext Transfer Protocol (HTTP) exchanges WWW documents written in HTML
• Simple Mail Transfer Protocol (SMTP) specifies electronic mail transfer
• Telnet logs into a computer system from a remote location

Port Numbers

• Servers and routers use the port number to control and process network traffic
• Ports are a numeric designation that corresponds to a particular high-level protocol
• For example, a firewall blocks external Telnet connections to a device inside the LAN by blocking all traffic on port 23

IP Addresses

• An Internet Protocol (IP) address is a unique numeric identifier for a device on a network
• IP address is comprised of numerical values separated by dots or colons
• IPv4 uses a 32-bit address.
• IPv6 uses a 128-bit address.

Domain Names

• Domain names are human-readable symbolic names associated with an IP address
• It is comprised of the computer name followed by the domain hierarchy
• For example, in 'matisse.cs.MIT.edu', 'matisse' is the computer name and 'cs.MIT.edu' is the domain hierarchy
• The Domain Name System (DNS) translates domain names into numeric IP addresses
• DNS is a distributed database, and since it is decentralized, domain name-to-IP mappings are managed at different levels

Common Top-Level Domains

• .com and .co for commercial
• .edu and .ac for educational
• .gov and .go for government
• .org and .or for non-profit organizations

Networks Summary

• Classifications can be based on geographic coverage (LAN, MAN, WAN), network topology (ring, star, bus), transmission method (wired, wireless), message switching methods (circuit, packet switching), and communication model (client/server, peer-to-peer)
• The Internet is the most notable internetwork, consisting of interconnected networks
• The OSI reference model splits communication into seven layers
• TCP/IP is a suite of protocols for interconnecting network devices on the internet
• IP addresses is a unique numerical identifier assigned to a device on a network
• Includes the Internet of Things, Cloud computing, Blockchain, and Al-driven networking.