The OSI (Open Systems Interconnection) model is a conceptual framework used to understand and implement network protocols in seven distinct layers.
1. Physical Layer
Function: Manages the physical connection between devices.
Components: Cables, switches, hubs, and other hardware.
Data Form: Bits (binary data).
2. Data Link Layer
Function: Provides node-to-node data transfer, error detection, and correction.
Components: MAC addresses, switches, and bridges.
Data Form: Frames.
Sub-layers: Logical Link Control (LLC) and Media Access Control (MAC).
3. Network Layer
Function: Handles routing, forwarding, and logical addressing.
Components: Routers, IP addresses.
Data Form: Packets.
Protocols: IPv4, IPv6, ICMP.
4. Transport Layer
Function: Provides end-to-end communication, error recovery, and flow control.
Components: Ports, sockets.
Data Form: Segments (TCP) or datagrams (UDP).
Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
5. Session Layer
Function: Manages sessions or connections between applications.
Components: Session checkpoints, dialogues.
Data Form: Data.
Protocols: PPTP (Point-to-Point Tunneling Protocol), RPC (Remote Procedure Call).
6. Presentation Layer
Function: Translates data between the application layer and the network. Ensures data is in a usable format and handles encryption/decryption.
Components: Codecs, encryption schemes.
Data Form: Data.
Protocols: SSL/TLS (Secure Sockets Layer/Transport Layer Security), JPEG, ASCII.
7. Application Layer
Function: Provides network services to end-users and applications.
Components: Network processes, application programs.
Data Form: Data.
Protocols: HTTP, FTP, SMTP, DNS.
Additional Key Points
Encapsulation: Data is wrapped with the necessary protocol information at each layer.
Decapsulation: The reverse process where data is unwrapped as it moves up the layers at the receiving end.
Layer Independence: Each layer operates independently, only interacting with adjacent layers.
Protocol Stack: Combination of protocols used in the OSI model to facilitate communication.
Importance of OSI Model
Standardization: Provides a universal set of standards to ensure different networks and devices can communicate.
Troubleshooting: Helps in diagnosing and resolving network issues by isolating problems to specific layers.
Interoperability: Ensures that products and software from different vendors can work together.
Educational Tool: Aids in understanding the complex process of network communication.
Common Protocols by Layer
Physical: Ethernet, USB, Bluetooth.
Data Link: Ethernet, PPP (Point-to-Point Protocol), Frame Relay.
Network: IP, IPX (Internetwork Packet Exchange), AppleTalk.
Transport: TCP, UDP, SCTP (Stream Control Transmission Protocol).
Session: NetBIOS (Network Basic Input/Output System), SMB (Server Message Block).
Presentation: SSL/TLS, JPEG, MPEG.
Application: HTTP, FTP, SMTP, POP3, IMAP, DNS.