The OSI model is a standard of the International Organization of Standardization (ISO).
It is a general purpose framework that characterizes and standardizes how computers communicate with one another over a network. Its 7-layered approach to data transmission divides the operations into specific related groups of actions at each layer.
each layer severs the layer above it and is served by the layer below it.
| Layer | Name | |
| 7 | Application | Data |
| 6 | Presentation | Data |
| 5 | Session | Data |
| 4 | Transport | Segment |
| 3 | Network | Packet |
| 2 | Data Link | Frame |
| 1 | Physical | Bits |
The TCP/IP Stack
The TCP/IP was developed in the 1960’s by the US Department of Defense (DoD) Advanced Research Projects Agency (ARPA)
It’s a protocol stack which consists of multiple protocols including Transmission Control Protocol (TCP) and Internet Protocol (IP).
It’s the main protocol used in computer operations today. Whereas OSI reference model is conceptual, the TCP/IP stack is used to transfer data in production networks.
The layers of the TCP/IP stack are equivalent to the OSI layers in operation and function.
| OSI Model | TCP/IP Stack | |
| Application | data | |
| Presentation | data | |
| Session | Application | data |
| Transport | Transport | segment |
| Network | Internet | packet |
| Datalink | frame | |
| Physical | Link | bits |
Communication between 2 or more hosts is called Protocol Data Unit (PDU).
