OSI/ISO reference model in communication system

Layer 1 (Physical): This layer considers only the physical

aspects of a network; the cables, converters, interconnecting

devices, etc.

Layer 2 (Data-link): This layer concerns itself with how Layers 1

and 3 work together.

Layer 3 (Network): This layer provides an addressing scheme

for routing of data and messages.

Layer 4 (Transport): This layer makes sure that messages get to

their correct destination.

Layer 5 (Session): This layer handles the actual connections

between systems.

Layer 6 (Presentation): This layer deals with the way different

systems represent data.

Layer 7 (Application): This layer concerns itself chiefly with the

software applications used on a computer screen