Which TCP/IP model layers relate to the OSI application layer?

In the TCP/IP model, one layer combines all three of the OSI's top layers at once.

#To the OSI application layer (L7),

#the Presentation layer (L6),

#the Session layer (L5),

there corresponds one layer of the TCP/IP model:

#Application Layer

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#Why is that?

TCP/IP is a practical model. It does not separate the application, presentation, and session layers, because modern protocols (HTTP, FTP, DNS, SMTP, TLS, and others) perform the tasks of all these layers at once:

• session management (OSI session layer)
• encryption/encoding (OSI presentation layer)
• application logic (OSI application layer)

That is why they are merged in TCP/IP.

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#Short answer for an interview

The OSI application layer actually corresponds to three OSI layers at once, 5, 6, and 7, and in TCP/IP they all correspond to one common layer: the Application Layer.

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#Cheat sheet (5 seconds)

OSI → TCP/IP:

• L5 Session → Application
• L6 Presentation → Application
• L7 Application → Application

In TCP/IP, all of this is one layer: the Application Layer.