14.1 Protocols

Purpose of Application Layer
- To provide services / interface with the user // access to applications, for example login, file transfer, network file access, email, etc
- To provide mechanisms for securing communication e.g. encryption/authentication
- To define/provide protocols used to allow the exchange of data/communication // to contain programs that exchange data
- Error detection and recovery mechanisms to handle application specific errors

Purpose of Transport Layer
- To provide logical communication between applications running on different hosts // To ensure that data is delivered to the correct application process on the destination machine
- To ensure error-free, end-to-end delivery of data between a source and a destination, in sequence // to provide error recovery techniques such as error detection codes and automatic repeat request
- To break data into segments when sent and to reconstruct when received // To reassemble segments at destination
- To regulate network connections // to provide flow control mechanisms to prevent data loss.

Secure Socket Layer (SSL) and Transport Layer Security (TLS) are two protocols.
- Ensure security/privacy when using the internet
- Data encryption
- Identification / authentication of client and server

Give two examples of situations where the use of SSL/TLS would be appropriate.
- When transmitting authentication data e.g. passwords, session cookies
- When transmitting data that must be protected from modification on its way to or from a server e.g. user input, or results from the server
- When transmitting data classified as non-public.