The Presentation Layer gets its name from its purpose: It presents data to the Application layer. It's basically a translator and provides coding and conversion functions. A successful data transfer technique is to adapt the data into a standard format before transmission. Computers are configured to receive this generically formatted data and then convert the data back into its native format for reading. By providing translation services, the Presentation layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another host.

The Session layer is responsible for setting up, managing and then tearing down sessions between Presentation layer entities. The Session layer also provides dialog control between devices, or nodes. It coordinates communication between systems and serves to organise their communication by offering three different modes: simplex, half-duplex and full-duplex. The session layer basically keeps one application's data separate from other application's data.

The Transport layer is responsible for providing mechanisms for multiplexing upper-layer application, session establishment, data transfer and tear down of virtual circuits. It also hides details of any network-dependent information from the higher layers by providing transparent data transfer.

The Network layer is responsible for routing through an internetwork and for networking addressing. This means that the Network layer is responsible for transporting traffic between devices that are not locally attached. Routers, or other layer-3 devices, are specified at the Network layer and provide routing services in an internetwork.

The Datalink ensures that messages are delivered to the proper device and translates messages from the Network layer into bits for the Physical layer to transmit. It formats the message into data frames (notice how we are not using the term segments) and adds a customized header containing the hardware destination and source address.