Overview
This lecture explains the application layer of the OSI model, its role in network communication, and how it compares to the TCP/IP model, focusing on protocols and network access methods.
OSI and TCP/IP Application Layers
- The OSI reference model is a layered guideline for designing network protocols.
- Information flows down from the application layer to the physical layer on the source host, then up to the application layer on the destination host.
- TCP/IP application layer protocols predate personal computers and multimedia, explaining the OSI model's extra layers.
- TCP/IP application layer roughly covers the top three OSI layers—application, presentation, and session.
- The workings of lower layers in both models are similar.
Application Layer Functions and Protocols
- Application layer provides software access to the network through applications or services.
- Opening a program like a web browser creates a process in memory at the application layer.
- Application layer protocols define rules for data exchange, including message types, syntax, formats, and error handling.
- Protocols must match on both source and destination hosts for successful communication.
Network Models: Client-Server and Peer-to-Peer
- Client-server model: client requests information, server responds; both operate at the application layer.
- Peer-to-peer (P2P) network design allows devices to act as both server and client, sharing resources directly.
- P2P can refer to both network design and applications enabling resource sharing.
Common Application Layer Protocols
- Application layer protocols manage user information exchange, defining necessary formats and controls.
- Examples include SMTP (email) and HTTP (web browsing).
- Many other protocols exist to support various communication functions.
Practical Importance
- Understanding application layer protocols assists in setting up services and solving network issues.
Key Terms & Definitions
- OSI Model — A multi-layer framework for network protocol design.
- TCP/IP Model — A suite of protocols governing internet communication.
- Application Layer — The top layer providing network services to end-user applications.
- Protocol — A set of rules governing data transmission.
- Client-Server Model — Network model where a client requests and a server provides resources.
- Peer-to-Peer (P2P) — Network where devices can act as both client and server.
- SMTP — Simple Mail Transfer Protocol, used for email transmission.
- HTTP — Hypertext Transfer Protocol, used for web communication.
Action Items / Next Steps
- Review the functions and relationships of OSI and TCP/IP layers.
- Familiarize yourself with major application layer protocols like HTTP and SMTP.