The OSI Model is composed of seven layers that make up the model. Each
layer is important to understand for proper understanding of network concepts of data packet creation and control. The layers start with Physical layer and end with the Application layer.
Physical Layer
The Physical layer is where the data is either put onto the media or received off the media. The media could be the network cable or wireless. The data is in the form of bits and is called Bits as the PDU (protocol data unit). These bits can be voltage levels that represent binary numbers of 1 or 0. They could also be light pules traveling on a fiber optic cable or radio wave pulses for a wireless network.
Data Link Layer
The Data Link layer is where framing of the data takes place. The Frame is the PDU name at this layer. The MAC (media access control) physical address is added or removed depending on which direction the data is traveling. The MAC address is used by switches to switch the data to the appropriate computer or node that it is intended for in a LAN (local area network).
Network Layer
The Network layer is where the IP (internet protocol) address is added or removed and the PDU at this layer is called a Packet. Routers operate at this level and use the IP (logical address) to route the data to the appropriate network. Network locations are found by the routers using routing tables to locate the appropriate networks.
Transport Layer
The Transport layer is where the data is segmented (broken into pieces) and used by the TCP protocol to ensure accurate and reliable data is transferred. The data segments are numbers so that proper sequencing can be determined on the receiving side in order to rebuild accurate files. The PDU name at this layer is called Segment.
Session Layer
The Session layer is where the session is created, maintained, and torn-down when finished.
Presentation Layer
The Presentation layer is where the data is formatted or decrypted into files that the user can understand.
Application Layer
The Application layer is the user interface to the network where that data is either being generated or received.
The study of Computer Network Training and the OSI Model can help you to prepare for certification and employment is this exciting field.