The Application Layer and Transport Layer are two layers of the TCP/IP protocol suite. Describe the purpose of the Application Layer and the purpose of the Transport Layer.

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

1. [1] (Application Layer) To provide services / interface with the user // access to applications, for example login, file transfer, network file access, email, etc
2. [1] (Application Layer) To provide mechanisms for securing communication e.g. encryption/authentication
3. [1] (Application Layer) To define/provide protocols used to allow the exchange of data/communication // to contain programs that exchange data
4. [1] (Application Layer) Error detection and recovery mechanisms to handle application specific errors
5. [1] (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
6. [1] (Transport Layer) 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
7. [1] (Transport Layer) To break data into segments when sent and to reconstruct when received // To reassemble segments at destination
8. [1] (Transport Layer) To regulate network connections // to provide flow control mechanisms to prevent data loss.
9. [1] Data are broken into equal sized packets
10. [1] Data packets have headers containing information such as the IP addresses of the sender and receiver
11. [1] Each packet of data is sent independently to the destination // Packets don't necessarily follow the same route
12. [1] Each packet is sent via the most optimum path available
13. [1] Packets don't necessarily arrive in the order they are sent // Packets are reconstructed at the destination in the correct order
14. [1] Missing / damaged packets are re-sent