OSI 7 Layer Model

In the networking world OSI stands for the Open Systems Interconnection, as in the Open Systems Interconnection Reference Model.

The OSI model breaks the various aspects of a computer network into seven distinct layers.

These layers are kind of like the layers of an onion: Each successive layer envelops the layer beneath it, hiding its details from the levels above. The OSI model is also like an onion in that if you start to peel it apart to have a look inside, you’re bound to shed a few tears.

The OSI model is not a networking standard in the same sense that Ethernet and TCP/IP are networking standards. Rather, the OSI model is a framework into which the various networking standards can fit. The OSI model specifies what aspects of a network’s operation can be addressed by various network standards. So, in a sense, the OSI model is sort of a standard of standards

Layer 1 is the Physical Layer, this covers cables and devices such as repeaters and hubs.

Layer 2 is the Data Link Layer, this covers providing MAC addresses identify network nodes. Bridges and switches are layer 2 devices.

Layer 3 is the Network Layer, this covers the routing of data.

Layer 4 is the Transport Layer, this covers the sending of data packets.

Layer 5 is the Session Layer, this covers the establishing of sessions between network applications

Layer 6 is the Presentation Layer, this covers the conversion of data so that it can be read by different systems

Layer 7 is the Application Layer, this covers the applications and allowing them to access network services.