Which layer exists in the OSI model but not in the TCP/IP model?

The Presentation layer exists in the OSI model but is not represented as a separate layer in the TCP/IP model. The OSI model uses seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The Presentation layer is responsible for data formatting, translation, encoding, compression, and encryption-related representation functions. In the TCP/IP model, these responsibilities are generally absorbed into the Application layer rather than separated into their own layer. The Network, Transport, and Application concepts all exist in both models, although naming and boundaries differ. For example, TCP/IP uses an Internet layer that maps closely to the OSI Network layer, and it has a Transport layer for protocols such as TCP and UDP. Understanding these differences matters because security controls often operate at different layers. Palo Alto Networks includes the TCP/IP model and OSI model, as well as devices operating across Layers 1 through 4, in the Network Fundamentals domain. Reference: Cybersecurity Apprentice Datasheet, Network Fundamentals 2.6 and 2.7.