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Networking: The OSI Model and the TCP Model

The OSI Model

OSI stands for Open Systems Interconnection. It is a standard and fundamental model for desribing how network communication is processed in a network device. The model has 7 layers:

7.Application Layer

6.Presentation Layer

5.Session Layer

4.Transport Layer

3.Network Layer

2.Data Link Layer

1.Physical Layer

The layers are stack on each other with layer 1, the physical layer, at the bottom.

Layer 1: The Physical Layer

This layer refers to the cabling and connectors that allow the communication signals to reach to the devices in the network.

This layer enables the communication in the same local area network. It is also called the switching layer. Here the network devices use MAC addresses to forward/send packets.

Layer 3: The Network Layer

This layer is also called the routing layer. In this layer, network devices use IP addresses to determine where to send network traffic.

Layer 4: The Transport Layer

This layer is responsible for providing the appropriate protocal for transporting data accross the network. This is where we can find TCP or UDP protocols.

Layer 5: The Session Layer

The session layer helps manage the communication between network devices using protocols like NetBIOS, SOCKS, and NFS.

Layer 6: The Presentation Layer

The presentation layer formats the data received into a format human can understand. For example png, mp4, and more.

Layer 7: The Application Layer

The application layer is the top layer in the OSI model. It provides an interface between the computer applications and the underlying network. We find http, dnf, ftp, in this layer.

The TCP/IP Model

The TCP/IP model is derrived from the OSI model but it has four layers instead of 7:

Layer 1: The Network Access Layer

This layer combines the physical layer and the data link layer from the OSI model into a single layer.

Layer 2: The Internet Layer

The network layer from OSI model becomes the internet layer.

Layer 3: The Transport Layer

The transport layer stayed the same.

Layer 1: The Application Layer

The session, presentation, and application layers from the OSI model are combined to become the application layer in the TCP/IP model.