Seven-layer OSI model

7-Layer-OSI-Model contains the following layers

7) Application Layer This is where you find applications like ping and telnet. It relies on all the layers below.

6) Presentation Layer MIME encoding, encryption and similar manipulation of the presentation of data is done at this layer.

5) Session Layer This layer is responsible for setting up and tearing down TCP/IP sessions.

4) Transport Layer The transport layer controls the reliability of a given link. Some protocols are stateful and connection oriented. This means that the session layer can keep track of the packets and retransmit those that fail.

3) Network Layer The network layer does routing, based on IP addressing. This is a logical addressing scheme - values are chosen by the network engineer. The addressing scheme is hierarchical.

2) Data Link Layer In this layer - bridges operate. The addressing scheme is physical which means that the addresses are hard-coded into the network cards at the time of manufacturer. The addressing scheme is flat.

1) Physical Layer The physical layer defines all electrical and physical specifications for devices. This includes the layout of pins, voltages, and cable specifications. Hubs and repeaters are pysical-layer devices.

This OSI model is roughly adhered to in the computing and networking industry. It's main feature is in the junction between layers which dictates the specifications on how one layer interacts with another. This means that a layer written by one manufacturer can operate with a layer from another. (Assuming that the specification is interpreted correctly.) These specifications are typically known as Request for Comment or "RFC"s. The OSI model is a good tool for use in the classroom, and a great favorite of interviewers!