Compare the OSI model with the TCP/IP model.
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The OSI model is a seven-layer conceptual reference model, while the TCP/IP model describes the Internet protocol suite and is commonly presented with four layers. TCP/IP combines the OSI session, presentation, and application functions into its application layer, and commonly combines OSI data-link and physical functions into its link or network-access layer. The transport and network/internet functions map closely between the models. OSI is mainly used as a framework for understanding, design, and troubleshooting; TCP/IP is the model reflected in deployed Internet protocols such as TCP, UDP, IP, HTTP, and DNS.
Purpose and structure
The OSI model standardizes networking functions into seven distinct layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It is a reference framework that helps describe how networking responsibilities can be separated.
The TCP/IP model is based on the Internet protocol suite and is commonly represented as four layers: Link (or Network Access), Internet, Transport, and Application. Some presentations use five layers by separating physical and data-link functions.
Layer mapping
The models do not map one-to-one at every boundary, but the following mapping is the usual comparison.
- TCP/IP Application: Corresponds broadly to the OSI Application, Presentation, and Session layers.
- TCP/IP Transport: Corresponds closely to the OSI Transport layer.
- TCP/IP Internet: Corresponds closely to the OSI Network layer.
- TCP/IP Link / Network Access: Covers functions broadly corresponding to the OSI Data Link and Physical layers in the four-layer presentation.
Protocols and practical use
The OSI model is not tied to one particular protocol suite; it provides a general way to classify networking functions. The TCP/IP model is closely associated with the protocols used for Internet communication.
For example, HTTP and DNS are application-layer protocols, TCP and UDP are transport-layer protocols, and IP operates at the Internet layer. In practice, engineers often use both models: TCP/IP to describe deployed protocol behavior and OSI terminology to isolate responsibilities during design and troubleshooting.