Osi

Front 1

This layer represents user applications, such as software for file transfers, for database access,
and for e-mail. It handles general network access, flow control, and error recovery.
Gateways commonly operate at this layer.

Back 1

Application

Front 2

This layer determines data exchange formats and translates specific files from the Application
layer format into a commonly recognized data format. It provides protocol conversion, data translation,
encryption, character-set conversion, and graphics-command expansion.

Back 2

Presentation

Front 3

This layer handles security and name recognition to enable two applications on different
computers to communicate over the network.

Back 3

Session Layer

Front 4

This layer provides flow control and error handling and is involved in correction of
transmission/reception problems. It also breaks up large data files into smaller packets, combines small packets
into larger ones for transmission, and reassembles incoming packets into the original sequence.

Back 4

Transport Layer

Front 5

This layer addresses messages and translates logical addresses and names into physical
addresses. It also manages data traffic and congestion involved in packet switching and routing.
Routers and wireless access points operate at this layer.

Back 5

Network Layer

Front 6

This layer is the interface between the upper "software" layers and the lower "hardware" Physical
layer. One of its main tasks is to create and interpret different frame types based on the network type in use.
The Data Link layer is divided into two sub-layers: the Media Access Control (MAC) sub-layer and the Logical
Link Control (LLC) sub-layer.
NICs, ISDN adapters, and bridges operate at this layer.

Back 6

Data-Link Layer

Front 7

This layer is the specification for the actual hardware connection, the electronics, logic circuitry,
and wiring that transmit the actual signal.
Hubs operate at this layer.

Back 7

Physical Layer