We have to learn about some basic terms before going into understanding of network layers. The following terms are useful to understand network concepts.
• Open systems – Systems that are open for communication with other systems
• ISO – International standards organization
• OSI – Open systems interconnection
• ISO/OSI – International standards organization for open systems interconnection
• Reference model of open systems interconnection is commonly referred as ISO/OSI
• ISO/OSI model uses 7 layers to organize a network into well defined, functional modules
• 7 Layers – Application, Presentation, Session, Transport, Network, Data-Link, Physical
Principles to develop these layers as per Andrew S. Tanenbaum.
- When there is a need of different level of abstraction, we should create a layer.
- Each and every layer should perform well defined function
- The function of each layer should be chosen according to the internationally standardized protocols.
- We should minimize the information flow across the interfaces while choosing layer boundaries
- We should not thrown distinct functions into same layer, so that the number of layers should be large enough.
- Also the number of layers should be small enough, so that the network architecture does not become unmanaged.
Brief about each layer’s function:
Application oriented and upper layers – Application, Presentation and Session Layers
Transmission oriented and lower layers – Transport, Network, Data-Link and Physical
- Physical layer: Lowest layer, Transmits data through network communication channels
- Data-link layer: Transfers raw data between Physical and Network Layers. Prevents data corruption, corrects errors and minimizes the flow of nformation across the physical and network layer boundaries
- Network layer: Determines route, handling network traffic, congestion, transfer speed, examines the network topology
- Transport layer: Transparent transfer, ensures data matching, manages the sending of data, determining its order and its priority
- Session layer: organizes and synchronizes the exchange of data between application processes, coordinating communications between different applications.
- Presentation layer: consolidates common functions, handles details related to the network’s interface to printers, file formats, video displays
- Application layer: end-user interface to the OSI system, file transfer, contains details about network-wide applications like e-mail and distributed databases