Network Models provide frameworks that guide how different devices communicate over a network.
- Open Systems Interconnection (OSI) Reference Model
- Internet Model (TCP/IP Model)
- Message Transmission Using Layers
1.) Open Systems Interconnection (OSI) Reference Model
The OSI Model is a conceptual framework developed by the International Organization for Standardization (ISO) to standardize network communication.
- It consists of seven layers, each with distinct responsibilities.
1.) Physical Layer:
The physical layer deals with the physical transmission of raw data over a communication medium (e.g., cables, radio waves) by defining the hardware elements involved in data transfer.
- Converts data into electrical signals or light pulses and transmits them across the transmission medium.
2.) Data Link Layer:
The data link layer is responsible for the reliable transfer of data frames between two devices on the same network by handling error detection and correction, as well as flow control.
- Handles error detection and correction, framing, and addressing (using MAC addresses).
3.) Network Layer:
The network layer is responsible for determining the best path for data transmission by managing logical addressing and routing of data packets across networks.
- Determines the best path for data using logical addressing (e.g., IP addresses).
4.) Transport Layer:
The transport layer ensures reliable data transfer between two systems by handling error correction, flow control, and retransmission of lost data.
- Provides two main types of data delivery: connection-oriented (TCP) and connectionless (UDP).
5.) Session Layer:
The session layer manages sessions between applications. It establishes, maintains, and terminates communication sessions between two devices or applications.
- Supports dialogue control, enabling devices to communicate in a half-duplex or full-duplex mode.
6.) Presentation Layer:
The presentation layer is responsible for translating, encrypting, and compressing data between the application and transport layers.
- It ensures that the data is in a format that the receiving application can understand.
- Ensures compatibility between different systems, handling character encoding and data conversion.
7.) Application Layer:
Application Layer is the topmost layer of the OSI model that directly interacts with end-user applications.
- It provides network services to the user, such as file transfer, email, and network management.
- It acts as an interface between the user and the network.
- Manages high-level protocols like HTTP, FTP, SMTP, allowing users to interact with network services.
Key Points: The OSI Model is theoretical and serves as a guideline for network communication. It is useful for troubleshooting and understanding how data flows through different network layers.
2.) Internet Model (TCP/IP Model)
The Internet Model, also known as the TCP/IP Model, is a more practical and widely used framework developed by the U.S. Department of Defense.
- It focuses on the core protocols of the Internet, namely Transmission Control Protocol (TCP) and Internet Protocol (IP).
This model has four layers:
- Application Layer
- Transport Layer
- Internet Layer
- Link Layer
1.) Application Layer:
The application layer in the TCP/IP model is responsible for providing end-to-end communication services to user applications.
- It defines protocols that allow software applications (like web browsers, email clients, etc.) to interact over a network.
- Supports protocols like HTTP, FTP, SMTP, allowing direct communication with network applications.
2.) Transport Layer:
The transport layer in the TCP/IP model is responsible for end-to-end communication between hosts by ensuring reliable data transfer, error correction, and flow control between devices.
- This layer provides transparent data transfer services to the application layer.
- Uses protocols like TCP (reliable, connection-oriented) and UDP (faster, connectionless) for data transfer.
3.) Internet Layer:
The internet layer is responsible for logical addressing, routing, and packet forwarding.
- It provides the necessary functions to ensure that data can be transferred across different networks (i.e., it handles communication between devices on different networks).
- Uses IP addressing for routing and delivers data to the correct network destination.
4.) Link Layer (Network Interface Layer):
The link layer is the lowest layer in the TCP/IP model that is responsible for the physical transmission of data on the network hardware (e.g., cables, wireless).
- This layer deals with the protocols that operate within a local network and provide the necessary support for the internet layer.
- Handles the physical transmission of data and basic addressing within the local network.
Key Points: The TCP/IP Model is simpler and more flexible than the OSI Model, making it widely adopted for real-world networking, especially for internet-based communication.
3.) Message Transmission Using Layers
In layered architecture of Network Model, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work.
In both the OSI and TCP/IP models, message transmission occurs through layer-by-layer communication, where each layer has specific functions:
Data Encapsulation:
The sending device’s application layer starts by generating data. Each layer then adds its own header information (metadata) to the data.
- For example, the transport layer adds port information, and the network layer adds the IP address.
Data Transmission:
The physical layer of the sending device converts the encapsulated data into electrical or optical signals and transmits it over the network.
- Intermediate devices like routers use headers to guide data packets to their destination.
Decapsulation at the Receiving End:
The receiving device’s physical layer receives the signals, and each layer removes the headers, passing the original data up to the next layer.
- This continues until the data reaches the application layer, which delivers it to the end-user application.
