Network layers and the OSI Model

Open Systems Interconnect Model

Source: Wikipedia

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or networking system into seven distinct layers. It provides a structured approach to understanding and designing network protocols and interactions.

• Layer 7 – Application
• Layer 6 – Presentation
• Layer 5 – Session
• Layer 4 – Transport
• Layer 3 – Network
• Layer 2 – Data Link
• Layer 1 – Physical

Each layer serves a specific purpose in the process of transmitting data over a network.

Application Layer (Layer 7)

The topmost layer is where the actual application or user interacts with the network. It provides various application services such as email, file transfer, and web browsing.

Protocols

HTTP, HTTPS, FTP, SMTP, POP3, IMAP, DNS

Algorithms

None (Application layer is primarily concerned with application-specific data and does not typically involve specific algorithms.)

Presentation Layer (Layer 6)

This layer is responsible for data translation, encryption, and compression, ensuring that data sent by the application layer is presented correctly to the application on the receiving end. It deals with issues like character encoding and data format conversion.

Protocols

SSL/TLS (for secure communication)

Algorithms

Data compression algorithms, encryption/decryption algorithms (e.g., AES, DES)

Session Layer (Layer 5)

The Session Layer establishes, maintains, and terminates connections between two devices, ensuring that data is synchronized and organized during the communication session. It can also handle tasks like session checkpointing and recovery.

Protocols

NetBIOS, RPC (Remote Procedure Call)

Algorithms

None (Session layer primarily deals with managing sessions and connections.)

Transport Layer (Layer 4)

The Transport Layer is responsible for end-to-end communication and ensures that data is reliably transmitted between two devices. It manages error detection, correction, and flow control.

Protocols

TCP (Transmission Control Protocol), UDP (User Datagram Protocol), SCTP (Stream Control Transmission Protocol)

Algorithms

Error checking and correction algorithms (e.g., checksums), flow control algorithms (e.g., sliding window), congestion control algorithms

Network Layer (Layer 3)

This layer deals with routing, addressing, and forwarding packets of data. It establishes logical paths between source and destination nodes in a network.

Protocols

IP (Internet Protocol), ICMP (Internet Control Message Protocol), OSPF (Open Shortest Path First), BGP (Border Gateway Protocol), RIP (Routing Information Protocol)

Algorithms

Routing algorithms (e.g., Dijkstra’s algorithm), IP addressing and subnetting algorithms

Data Link Layer (Layer 2)

The Data Link Layer is responsible for creating a reliable link between two directly connected nodes, ensuring data integrity and error detection.

Protocols

Ethernet, PPP (Point-to-Point Protocol), Wi-Fi (802.11), MAC (Media Access Control) addresses

Algorithms

Ethernet frame encoding/decoding, error detection and correction (e.g., CRC)

Physical Layer (Layer 1)

This layer deals with the physical medium and transmission of raw bits over a physical connection, such as cables, switches, and network interfaces. It defines characteristics like voltage levels, connectors, and data rates.

Protocols

Ethernet, Wi-Fi, DSL (Digital Subscriber Line), Fiber Optics

Algorithms

Modulation and demodulation (e.g., QAM, PSK), signal encoding, error handling