Osi Layers

Front 1

Physical Layer

Back 1

#1

Responsible for placing the network data on the wire, by changing binary data into electrical pulses on the physical medium.

Physical topology is defined at this level

Front 2

Data Link Layer

Back 2

#2

Responsible for the logical topology and logical (MAC) addressing. Individual network card addresses also function at this level.

Front 3

Network Layer

Back 3

#3

Responsible for logical network addressing. Some error control and flow control is performed at this level.

Front 4

Transport Layer

Back 4

#4

Responsible for providing reliable end-to-end communications. Includes most of the error control and flow control.

Front 5

Session Layer

Back 5

#5

Responsible for establishing and maintaining a communications "session."

Front 6

Presentation Layer

Back 6

#6

Responsible for the presentation of data (for example, the translation of character sets - e.g., ASCII to EBCDIC).

Front 7

Application Layer

Back 7

#7

Responsible for providing network services - like file services, print services, and messaging services (not applications like word processing or spreadsheets, as the layers name might lead you to believe)