INTRODUCTION TO COMPUTER NETWORK

PHYSICAL LAYER

DATA LINK LAYER

NETWORK LAYER

TRANSPORT LAYER

MCQ- COMPUTER NETWORK

APPLICATION LAYER

NETWORK SECURITY

MULTIMEDIA AND FUTURE NETWORKING

COMPUTER NETWORK LAB WORK

OSI Reference Model

COMPUTER NETWORK NOTES(IOE, BSCCSIT,BCA)

OSI REFERENCE MODEL 

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. It was developed by the International Organization for Standardization (ISO) to promote interoperability and facilitate understanding and design of network architectures. Each layer in the OSI model has a specific function, and communication between layers is achieved through well-defined interfaces. 

Physical Layer (Layer 1):

The physical layer deals with the physical connection between devices. It specifies the characteristics of the hardware, such as cables, connectors, and signaling methods, needed to transmit raw bits over a physical medium.

Features:

  • Deals with the physical connection of devices.
  • Transmits raw binary data (0s and 1s) over cables or wireless.
  • Defines hardware specifications (e.g., cables, connectors, transmission rates).
  • Manages signal encoding, bit synchronization, and modulation.
  • Examples: Ethernet cables, fiber optics, Bluetooth, Wi-Fi.

Data Link Layer (Layer 2):

The data link layer provides error detection and correction, as well as the framing of data into frames for reliable transmission over the physical layer. It also manages access to the physical medium through protocols like Ethernet.

Features:

  • Handles error detection and correction in data transmission.
  • Uses MAC (Media Access Control) addresses for device identification.
  • Controls access to the physical medium (e.g., CSMA/CD for Ethernet).
  • Divided into two sublayers:
  •          Logical Link Control (LLC): Error handling and flow control.
  •          Media Access Control (MAC): Access control and addressing.
  • Examples: Ethernet, Wi-Fi (802.11), MAC addresses, switches.

Network Layer (Layer 3):

The network layer is responsible for logical addressing, routing, and forwarding of data packets between devices on different networks. IP (Internet Protocol) operates at this layer.

Features:

  • Responsible for routing and logical addressing (IP addresses).
  • Uses packet switching for data transmission.
  • Supports fragmentation (dividing large packets into smaller ones).
  • Manages congestion control and network traffic flow.
  • Examples: IP (Internet Protocol), routers, IPv4, IPv6.

Transport Layer (Layer 4):

The transport layer ensures end-to-end communication and data flow control. It manages segmentation, reassembly, error recovery, and flow control. Examples of transport layer protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Features:

  • Ensures end-to-end communication and error recovery.
  • Provides segmentation and reassembly of messages.
  • Implements flow control to prevent data overflow.
  • Uses TCP (connection-oriented, reliable) and UDP (connectionless, faster).
  • Examples: TCP, UDP, port numbers.

Session Layer (Layer 5):

The session layer establishes, manages, and terminates sessions (dialogues) between applications. It handles the synchronization and coordination of data exchange between systems.

Features:

  • Manages sessions (establishment, maintenance, and termination of connections).
  • Supports authentication and authorization.
  • Handles dialog control (full-duplex/half-duplex communication).
  • Ensures proper synchronization between sender and receiver.
  • Examples: NetBIOS, RPC (Remote Procedure Call).

Presentation Layer (Layer 6):

The presentation layer is responsible for data translation, encryption, and compression. It ensures that data is presented in a readable format for the application layer. It also handles character encoding, data compression, and encryption/decryption.

Features:

  • Formats and translates data between applications and networks.
  • Handles encryption, compression, and encoding of data.
  • Ensures data structure compatibility (e.g., ASCII, JPEG, MP3).
  • Examples: SSL/TLS (encryption), JPEG, GIF, MPEG, ASCII.

Application Layer (Layer 7):

The application layer provides network services directly to end-users or applications. It allows software applications to communicate over a network. Protocols such as HTTP (Hypertext Transfer Protocol), FTP (File Transfer Protocol), and SMTP (Simple Mail Transfer Protocol) operate at this layer.

Features:

  • Interfaces with user applications (e.g., web browsers, email clients).
  • Provides network services like file transfer, email, and remote login.
  • Uses protocols for communication (e.g., HTTP for web browsing).
  • Examples: HTTP, FTP, SMTP, DNS, Telnet, SSH.

 

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