OSI model

• abbreviation full form: Open Systems Interconnection (OSI)
• is divided into 7 layers
• the first

the 7 layers:

Physical layer:

• what it does: sends raw bits over a medium like cables, hubs and other stuff
• mainly focuses on the signal transmission itself not the data

Data link layer:

• what it does: takes care of the node to node connection and correction plus framing as well through switches and node to node data transfer, error detected bridges
• has two sub layers: (will look into it later)
  • Media access control (MAC)
  • Logical link control (LLC)

Network layer:

• what this one does: handles packet routing and stuff like logical addressing (for example IP addresses). basically determines the best path for data to travel from source to destination

Transport layer:

• takes care of the data transfer along with error recovery, segmentation and flow control
• uses two key protocols:
  • TCP : connection oriented, reliable data transfer
  • UDP : connectionless but less reliable data transfer

Session layer:

• manages the establishment, management and termination of sessions (connections) between apps

Presentation layer:

• translates data between the network and the application. basically takes care of the data encryption, decryption, compression and format translation.
• ensures the data is in a usable form between layers

Application layer:

• what the user actually sees and uses
• commonly used protocol examples:
  • HTTP and HTTPS for web browsing and stuff
  • FTP for file transfer purposes
  • SMTP for email communication