Overview
This lesson introduces the application layer in networking, explaining how various application protocols enable different software and services to communicate over a network.
Review of OSI Layers
- The physical layer handles the transmission of electrical or optical signals.
- The data link layer manages addressing and data transfer between devices (e.g., Ethernet).
- The network layer enables communication across different networks using IP.
- The transport layer (TCP/UDP) ensures correct delivery to applications.
Application Layer Basics
- The application layer enables software applications to send and receive data across networks.
- Application data is carried in the payload section of TCP segments.
- The payload might include web pages, streamed videos, or printer documents.
- There are many protocols at the application layer, each suited to specific application types.
- Application layer protocols are standardized for interoperability between different software.
Application Layer Protocol Examples
- Web browsers (clients) and web servers (servers) must use the same protocol to communicate.
- Popular web browsers include Chrome and Safari; common web servers are IIS, Apache, and Nginx.
- HTTP is the standard application layer protocol for web traffic.
- All browsers and servers use HTTP to ensure any browser can talk to any server.
- Other application classes, like FTP, also require all clients and servers to use the same protocol.
Key Terms & Definitions
- Application Layer — The top layer in the network model providing interfaces for software to communicate over a network.
- Payload — The actual data sent by applications, carried inside transport layer segments.
- Protocol — A set of rules and conventions to allow systems to exchange data reliably.
- HTTP — HyperText Transfer Protocol, the standard protocol for web communication.
- Interoperability — The ability of different systems and applications to work together using common protocols.
Action Items / Next Steps
- Review examples of application layer protocols (HTTP, FTP).
- Identify which protocols are used by common applications you use.