Overview
This lecture discusses the application layer of the OSI model, its relation to the TCP/IP model, core networking protocols, and models for device communication.
OSI and TCP/IP Application Layers
- The OSI model is a layered framework for network protocol design, with data passing through each layer.
- The application layer is the top OSI layer and is where network communications start and end for users.
- TCP/IP application layer protocols align with the top three OSI layers (application, presentation, session).
- Additional OSI layers exist due to TCP/IP protocols being created before modern interfaces and media.
Application Layer Function and Protocols
- Applications and services in the application layer allow devices to access the network.
- A process begins when a user opens a network application (e.g., web browser or messaging app).
- Application layer protocols standardize data exchange rules between networked applications.
- Protocols define message formats, control commands, data types, syntax, and error handling.
- Matching application protocols must be present on source and destination hosts for successful communication.
Communication Models: Client-Server and Peer-to-Peer
- The client-server model involves clients requesting information and servers responding, both at the application layer.
- Peer-to-peer (P2P) networking includes P2P network design and P2P applications.
- In P2P networks, devices can act as both server and client, sharing resources without a dedicated server.
Common Application Layer Protocols
- Key TCP/IP application layer protocols for data exchange include SMTP (email) and HTTP (web).
- Many other protocols support various network communication functions.
Key Terms & Definitions
- OSI Model — A seven-layer framework for network protocol design.
- Application Layer — The layer where user interaction with networked applications occurs.
- Protocol — A set of rules for formatting, transmitting, and interpreting data.
- Client-Server Model — A communication model where clients request and servers provide resources.
- Peer-to-Peer (P2P) — A network model where devices share resources directly as both clients and servers.
- SMTP — Simple Mail Transfer Protocol for sending emails.
- HTTP — Hypertext Transfer Protocol for web communication.
Action Items / Next Steps
- Review examples of application layer protocols.
- Study how client-server and peer-to-peer models work in real networks.