If you use either Telnet or FTP, which is the highest layer you are using to…

Concept

The OSI reference model organises network communication into seven layers, from the lowest (Physical) up to the highest (Application). The Application layer is the top layer — it is the one that interacts directly with end-user network services and the programs a person actually runs. A protocol's place in the stack is fixed by what job it does, not by the data it happens to carry.

Applying it here

Both Telnet (remote terminal access) and FTP (file transfer) are end-user network services: a user invokes them directly to do useful work over the network. Services that users invoke directly live at the very top of the stack — the Application layer. So whichever of the two you use, the highest layer you are operating at is the Application layer.

Why the other layers are not the answer

• Transport delivers byte streams or datagrams between endpoints (the job TCP/UDP do). FTP and Telnet sit on top of TCP and use it, so Transport is below them — not the highest layer in use.

• Session manages dialogue setup, checkpointing and synchronisation between two sides; it is one layer below the top and does not itself house the user-facing service.

• Presentation handles data representation, encoding and encryption for the layer above it; it serves the Application layer rather than being the topmost layer the user drives.

The topmost layer involved when running Telnet or FTP is therefore the Application layer.