Chapter 2_ Application Layer.pdf

Chapter 2: Application Layer PowerPoint: CIS3347_13e_Ch02_ApplicationLayer v1.1 (1).pdf Introduction The application layer is where user-facing applications interact with the underlying network to send and receive data. It enables communication between software and network serv...

Chapter 2: Application Layer PowerPoint: CIS3347_13e_Ch02_ApplicationLayer v1.1 (1).pdf Introduction The application layer is where user-facing applications interact with the underlying network to send and receive data. It enables communication between software and network services, handling processes such as email, web browsing, and file transfers. Application Architectures Different architectures determine how applications are structured and where processing occurs in the network. Host-Based Architectures Host-based architecture places all processing on a central server (host). ○ Clients are typically terminals or thin clients that only capture input and display output. ○ Advantages: Centralized control and management. ○ Disadvantages: The server can become a bottleneck with heavy loads, and upgrading requires costly changes to the server. Client-Based Architectures In client-based architectures, the client performs most of the processing, while the server only provides data storage. ○ Advantages: Reduces the load on the server and allows clients to handle processing locally. ○ Disadvantages: Increased network traffic and client-side complexity. Client–Server Architectures Client-server architectures distribute processing between clients and servers. ○ Two-tier architecture: Processing is split between client and server. ○ Three-tier architecture: Adds a middle layer (e.g., an application server) to handle business logic, separating it from the data and presentation layers.  ○ n-tier architecture: Further separates tasks across multiple servers (e.g., a web server, an application server, and a database server). ○ Advantages: Efficient use of resources, scalability, and flexibility. ○ Disadvantages: More complex to manage than simpler architectures. Cloud Computing Architectures Cloud computing delivers resources (computing power, storage, and services) over the internet, allowing users to access them on demand. ○ Types: Infrastructure as a Service (IaaS): Provides virtualized computing resources. Platform as a Service (PaaS): Offers platforms for building and deploying applications. Software as a Service (SaaS): Delivers software applications over the internet. ○ Advantages: Scalability, flexibility, reduced capital expenditure. ○ Disadvantages: Security concerns and reliance on internet connectivity. Peer-to-Peer Architectures In peer-to-peer (P2P) architectures, all devices (peers) share resources and processing power equally, without relying on a central server. ○ Advantages: No central bottleneck, improved fault tolerance. ○ Disadvantages: Difficult to manage, prone to security vulnerabilities. Choosing Architectures When choosing an architecture, factors such as scalability, maintenance, security, and network traffic should be considered. Organizations should also weigh the costs of implementation and ongoing management. World Wide Web The World Wide Web (WWW) is a system of interlinked hypertext documents accessed via the Internet, primarily using web browsers. How the Web Works The web works through a client-server model, where web browsers (clients) request web pages from servers. HTTP (Hypertext Transfer Protocol) is the primary protocol used for requesting and transmitting web content. Inside an HTTP Request A client sends an HTTP request to a server to access a web resource (e.g., a webpage). Components of an HTTP request include: ○ Request Line: Specifies the HTTP method (e.g., GET, POST), URL, and HTTP version. ○ Headers: Contain metadata such as browser type and supported content types. ○ Body: Optional, used to send data in POST requests (e.g., form data). Inside an HTTP Response The server responds to the client with an HTTP response. Components of an HTTP response include: ○ Status Line: Includes the HTTP version, status code (e.g., 200 OK, 404 Not Found), and a message. ○ Headers: Provide information like content type and length. ○ Body: Contains the requested content (e.g., HTML for a webpage). Electronic Mail Email is one of the most widely used internet applications, allowing users to send and receive messages across networks. How Email Works Email follows a client-server model, where an email client sends messages to an email server, which forwards them to the recipient’s server. Protocols: ○ SMTP (Simple Mail Transfer Protocol): Used for sending emails. ○ IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol): Used for receiving emails. Inside an SMTP Packet An SMTP packet includes: ○ Sender and recipient addresses. ○ Message body: The content of the email. ○ Attachment data: If applicable, included using MIME (Multipurpose Internet Mail Extensions). Attachments in Multipurpose Internet Mail Extension (MIME)  MIME allows binary files (like images or documents) to be attached to emails by encoding them as ASCII text. MIME types describe the content type (e.g., text/html, image/jpeg). Other Applications Several other applications utilize the application layer for specialized network tasks. Telnet Telnet is a protocol used to remotely access another computer’s command-line interface over a network. It’s commonly replaced by more secure protocols like SSH (Secure Shell). Videoconferencing Videoconferencing allows real-time video communication between multiple users over the internet. It uses protocols like RTP (Real-time Transport Protocol) to ensure the smooth transmission of video and audio streams. Implications for Cyber Security The application layer is particularly vulnerable to security threats, as it interfaces directly with users. Common security issues include: ○ Phishing attacks via email. ○ Cross-site scripting (XSS) and SQL injection on web applications. ○ Malware is delivered through email attachments or malicious websites. Security measures: Encryption (e.g., HTTPS for web traffic), user authentication, email filtering, and the use of secure protocols (e.g., SSH instead of Telnet). Key Concepts to Remember Application Architectures: Understand the different types (host-based, client-based, client-server, cloud computing, peer-to-peer) and how they affect processing, scalability, and security. World Wide Web: Know how HTTP works and the structure of HTTP requests and responses. Email: Be familiar with SMTP, IMAP, and POP3, and how MIME handles attachments. Other Applications: Understand the basics of Telnet and videoconferencing technologies.  Cybersecurity: Application-layer vulnerabilities and countermeasures are critical in securing communication across the network.