TCP/IP in Internet architecture
The OSI model is an abstract reference model. The TCP/IP model is a practical description of the Internet protocol suite. It was developed before the OSI model and, in the common four-layer view, includes the application, transport, Internet, and network access layers. The last covers link and physical-medium functions. It combines functions from several OSI layers, which supports an implementation-oriented description. Layer names and boundaries depend on the version of the model being used.
The model describes data exchange between computers, addressing, and forwarding packets to destinations across different networks. This division can describe services such as voice calls, video streaming, and web browsing.
The four layers of the TCP/IP model
In the four-layer view, the TCP/IP suite contains distinct layers, each with its own scope of functions and protocols.
4. Application Layer
The top layer includes the protocols through which applications use the network. These protocols define data-exchange formats, encoding, and dialogue rules for particular services.
- Responsibilities: Direct interaction with user applications, data representation, encoding, and dialogue control.
- Key Protocols: , , , .
3. Transport Layer
The Transport Layer provides end-to-end communication between devices. Depending on the protocol, it may provide segmentation, error control, flow control, and reliability mechanisms.
- Responsibilities: Data delivery according to the protocol, error checking, segmentation.
- Key Protocols: , .
2. Internet Layer
The Internet Layer handles addressing and forwarding packets between different networks, or internetworking. It is a central part of the TCP/IP model.
- Responsibilities: Logical addressing, routing, packet forwarding.
- Key Protocols: is the central element of this layer.
1. Network Access Layer
This layer enables transmission on a directly connected network, covering link and medium functions. It includes hardware details such as cabling, framing, and signaling.
- Responsibilities: Medium access, framing, and data transmission.
- Key Technologies: , .
Comparing the TCP/IP and OSI models
Both models describe network communication, but they have different structures and scopes. TCP/IP organizes existing Internet protocols into a practical description. OSI defines abstract layer functions as a reference model. Common layer mappings are approximate because individual protocols may cover functions from several layers.
How the layers map
- Approximately, the TCP/IP Application Layer covers the OSI Application, Presentation, and Session layers (Layers 7, 6, 5).
- The TCP/IP Transport Layer corresponds to the functions of the OSI Transport Layer (Layer 4).
- The TCP/IP Internet Layer corresponds to the functions of the OSI Network Layer (Layer 3).
- The TCP/IP Network Access Layer covers functions of the OSI Data Link and Physical layers (Layers 2, 1).