What is the OSI Model?
The OSI stands for Open Systems Interconnection. It is a set of rules that explains how different computer systems communicate over a network.
The OSI model was developed by the International Organization for Standardization (ISO). OSI model consists of 7 layers and each layer has specific functions and responsibilities.
What are the 7 Layers of the OSI Model?
The 7 layers of the OSI model are :
Application
Presentation
Session
Transport
Network
Data Link
Physical
Explain the 7 layers of the OSI Model:
7. Application Layers:
The application layer is used by network applications. Network applications are computer applications that use Internet.
Network applications use application layer protocols to do different tasks. Some of them are:
File Transfer ⇒ FTP protocol
Web Surfing ⇒ HTTP/HTTPS protocol
Email ⇒ SMTP protocol
Virtual Terminals ⇒ Telnet protocol
So the application layer provides the services to the network application with the help of protocols to perform user activities.
6. Presentation Layer:
Translation:
The presentation layer receives data from the application layer. The presentation layer converts the received data into machine-understandable binary format.
Data Compression:
After converting that data then it compresses the data by bit reduction. It reduces the bit that represents the original data. The bit reduction can be lossy or lossless. By the bit reduction, the data is compressed so that the data transmission can be faster
Encryption/Decryption:
To maintain the integrity of data before transmission data is encrypted. Encryption enhances the security of data. At the sender end the data is encrypted and sent to the receiver. After reaching to the receiver end the data is decrypted.
5. Session Layer:
The Session Layer takes care of the communication sessions between two devices. The session layer manages sessions, including synchronizing them and maintaining connections.
The Popular Session Layer Protocols are:
ASP ⇒ AppleTalk Session Protocol
H.245 ⇒ Call Control Protocol for Multimedia Communication
PAP ⇒ Password Authentication Protocol
NetBIOS ⇒ Network Basic Input Output System
4. Transport Layer:
The transport layer provides end-to-end communication services for applications. It ensures complete data transfer and proper data segmentation from the sending to the receiving host. Key responsibilities include:
Segmentation and Reassembly: Data from the application layer is broken into manageable segments, and then reassembled correctly at the destination.
Error Detection and Recovery: The transport layer detects errors and manages retransmissions to ensure reliable data transfer.
Flow Control: It manages the rate of data transmission between devices to prevent network blocking.
Popular transport layer protocols are:
TCP (Transmission Control Protocol): Provides reliable, connection-oriented data transmission.
UDP (User Datagram Protocol): Offers a faster, connectionless transmission.
3. Network Layer:
The network layer is responsible for routing packets between devices across different networks. It determines the best path for data to travel based on logical addressing and network conditions.
Logical Addressing: Uses addresses such as IP addresses to identify devices uniquely on a network.
Routing and Forwarding: Determines the optimal path for data and forwards packets toward their destination.
Fragmentation and Reassembly: Breaks packets into smaller units if necessary and reassembles them at the receiving end.
Key network layer protocols include:
IP (Internet Protocol): Fundamental protocol for addressing and routing data packets.
ICMP (Internet Control Message Protocol): Used for error reporting and diagnostics.
IGMP (Internet Group Management Protocol): It Manages multicast group memberships.
2. Data Link Layer:
The data link layer handles communication between devices on the same network segment. It is responsible for packaging data into frames and ensuring that these frames are delivered without errors.
Framing: Converts raw bits from the physical layer into frames, adding necessary control information.
Error Detection and Correction: Uses methods such as CRC (Cyclic Redundancy Check) to detect and sometimes correct errors that occur during data transmission.
Medium Access Control (MAC): Controls how devices on the same network share access to the physical medium.
Common protocols and standards at the Data Link layer:
Ethernet: A widely used LAN technology.
PPP (Point-to-Point Protocol): Used for direct connections between two nodes.
MAC Addressing: Unique hardware addresses assigned to network interfaces.
1. Physical Layer:
The physical layer is the foundation of the OSI model, dealing with the actual transmission of raw binary data over a physical medium.
Signal Transmission: Converts digital data into electrical, optical, or radio signals suitable for transmission.
Hardware Specifications: Defines the physical characteristics of the transmission media, such as cables, switches, and connectors.
Bit Stream Transmission: Manages the continuous stream of bits and handles issues like voltage levels, timing, and physical data rates.
Standards governing the physical layer include specifications like IEEE 802.3 for Ethernet and various cable standards. It defines the physical layer and media access control (MAC) sublayer of the data link layer in the OSI model, essentially outlining how data is physically transmitted over a network using Ethernet.
The OSI model serves as a fundamental framework for understanding how data is transmitted across networks.