Application layer (4) - includes application, presentation and session layers of the OSI model, which significantly simplifies network troubleshooting.Comparing to the OSI model, TCP/IP is a 4-layer model: This model has the same purpose as the OSI model but fits better into modern network troubleshooting. Layer 1 (Physical) - Communication media that sends and receives bits, electric signaling, and hardware interface.Layer 2 (Data link) - Data is encapsulated within a custom header, either 802.3 (Ethernet) or 802.11 (wireless) and is called "frame", handles flow control.Layer 3 (Network) - responsible for logical device addressing, data is encapsulated within an IP header and now called "packet".Layer 4 (Transport) - transport layers primary responsibility is assembly and reassembly, a data stream is divided into chunks (segments), assigned sequence numbers and encapsulated into protocol header (TCP, UDP, etc.).Layer 5 (Session) - responsible for setting up, managing and closing sessions between client and server.Encryption is done here (but in reality it may not be true, for example, IPSec) Layer 6 (Presentation) - ensures data is received in a usable format.If the web browser wants to download an image, the protocol will organize and execute the request Layer 7 (Application) - a protocol that defines the communication between the server and the client, for example, HTTP protocol.
The OSI model was originally conceived as a standard architecture for building network systems, but in real-world networks are much less defined than the OSI model suggests. The Open Systems Interconnection (OSI) model is a 7-layer model that today is used as a teaching tool. Both models help to visualize how communication between nodes is happening.
To understand the concept of how node to node communication happens, let's get familiar to the OSI model and TCP/IP model. Computer networks consist of many different components and protocols working together.
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