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OSI model

OSI model

(also open systems interconnection model)

OSI model definition

Conceptual model created by the International Organization for Standardization for enabling different systems to communicate by using standard protocols. The OSI model is a universal language for computer networking, based on splitting up the communication system into seven layers stacked upon each other.

OSI model layers

  • Physical layer. This layer is responsible for the wireless or cable connection between network nodes and for transmitting the raw data.
  • Data link layer. This layer is responsible for establishing and terminating a connection between two physically connected network nodes.
  • Network layer. This layer has two functions: 1) breaking up segments into packets and then reassembling the packets on the receiving end; 2) discovering the best path through a network and routing the packets across it — the network layer uses IP addresses to route the packets.
  • Transport layer. This layer breaks data into segments on the transmitting end and reassembles it on the receiving end. It is responsible for sending out the data at a rate that the receiving device can receive and checking whether it was received correctly.
  • Session layer. This layer creates sessions between devices and is responsible for opening them, maintaining them while the data is being transmitted, and closing them when communication ends.
  • Presentation layer. This layer prepares data for the application layer by defining how devices should encrypt, compress, and encode the data so that it is received without errors on the other end.
  • Application layer. This is the human-computer interaction layer, where an end-user software (e.g., email client, browser) sends and receives data by using application-layer protocols, like HTTP or DNS.

Further reading

Ultimate digital security