TCP/IP Model in Computer Networks (Fully Explained)
The Transmission Control Protocol/Internet Protocol (TCP/IP) model serves as a simplified version of the OSI Model. The TCP/IP protocol suite was created prior to the OSI model. However, the layers within the TCP/IP protocol suite do not align perfectly with those in the OSI model.
TCP/IP Protocol
The original TCP/IP protocol consists of four layers: host-to-network, Internet, Transport, and Application layer. The host-to-network layer corresponds to the combined physical and data link layers found in the OSI model. The Internet layer in TCP/IP matches the Network layer of the OSI model.
Additionally, the Application layer encompasses the functions of the Session, Presentation, and Application layers, along with the Transport layer in TCP/IP. In the TCP/IP model, the first four layers deliver physical standards, network interface, internetworking, and transport functions.
The uppermost layers (application, presentation, and session layers) in the OSI model are represented in TCP/IP by a single layer known as the application layer. Within the Transport layer, the TCP/IP model specifies three protocols: Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Stream Control Transmission Protocol (SCTP).
TCP/IP Protocol Suite to OSI Reference Model
The diagram below illustrates how the TCP/IP Protocol Suite maps to the OSI Reference Model:
Layers of TCP/IP Model
1. Application Layer
In TCP/IP, the Application layer protocols offer services to the application software operating on a computer. This layer utilizes protocols such as HTTP, POP3, and SMTP. It acts as an interface between the software on a computer and the network itself.
2. Transport Layer
In TCP/IP, the Transport layer comprises the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP provides services to the application layer that exists above the transport layer or higher within the TCP/IP model.
3. Internet Layer (Network Layer)
The Internet layer in the TCP/IP model corresponds to Layer 3 of the OSI model, known as the Network Layer. It is responsible for storing IP addresses and routing information. When data is sent from a node on one Local Area Network (LAN) to a node on another LAN, the Internet Layer facilitates this process. The protocols associated with the Internet Layer in TCP/IP include IPv4, IPv6, ICMP, and various routing protocols.
4. Host-to-Network or Link Layer
In the TCP/IP model, the Host-to-Network layer is referred to as the network interface or link layer. This layer provides essential services to the upper layers of the model. When a host or router's IP process decides to transmit an IP packet to another router or host, it relies on the link-layer information to forward that packet to the next destination.
This layer represents the lowest level of the TCP/IP model and focuses on the physical transmission of data. It effectively combines the functions of the data link layer and the physical layer found in the OSI model.
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