Which layers of the OSI reference model are host-to-host layers ?

Answer: Transport, Session, Presentation, Application (layers 4–7) are the host-to-host layers.

Why these are host-to-host layers:

• Transport: provides end-to-end communication between processes on different hosts (segmentation, ports, reliability or best-effort delivery).

• Session: establishes, manages and terminates sessions (dialog control) between applications on different hosts.

• Presentation: handles data representation, encryption and compression so communicated data is understood by the receiving host.

• Application: provides network services directly to user applications (for example HTTP, SMTP, file transfer), enabling host-level application communication.

In contrast, the lower layers (Physical, Data-link, Network) focus on node-to-node or link-level transmission and routing rather than end-to-end host communication.