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OSI Model

Data Networking#

Moving digital information from one place to another

OSI (Open Systems Interconnect) model#

It’s a way of modelling the system or network that is used for moving digital information from one place to another

Layers of the OSI model#

Physical layer (layer 1)#

  • Consists of all the physical medium like wire and electromagnetic spectrum and the protocols that have to be followed by these medium
  • Wires like Twisted Pair, CoAx, fibre optic cables, proprietary copper cables

Data Link layer (layer 2)#

  • Physical connections can be divided into network segments connecting one device to another
  • Each of the network segments uses a protocol to talk to each other
  • Ethernet and Wireless ethernet are some of the most commonly used protocols for connecting devices
  • For example the Ethernet protocol helps a computer connect to a router
  • And similar protocols help move data just between two devices and it’s a small hop
  • These protocols that are used for connecting two devices in a network segment are part of the data link layer

Network layer (layer 3)#

  • Network layer makes transporting information from a source device all the way to a destination device possible
  • It uses IP Addressing to assign IP addresses to all the devices on the internet
  • And uses IP Routing to route data from the source all the way to the destination device through a myriad of intermediary devices

Transport layer (layer 4)#

  • An analogy explaining the function of the transport layer is establishing a phone connection between two individuals trying to communicate over a telephone.
  • In order to communicate over a telephone one of the participants needs to dial the number of the other participant and wait for the other participant to pick up the call, and once the other participant has picked up the call and said hello then the former participant has to acknowledge it by saying hello again only after that the actual communication can happen
  • Similarly in data networks a connection/session has to be established between the source and the destination devices before moving data between them

Session and Presentation layer (layer 5, 6)#

Application layer (layer 7):#

  • In the application layer application specific protocols are used by the client and the server to request and receive application specific data
  • For example HTTP/HTTPS is an application level protocol in which the clients send a HTTP request to the servers and the servers in turn send a HTTP response