ISO OSI model

ISO: International Organization for Standardization.

OSI: Open Systems Interconnection.

The ISO OSI model is a reference framework that explains the process of transmitting data between computers. It consists of seven layers, each with specific functionality:

1. Physical Layer (Layer 1):

• Responsible for the actual physical connection between devices.
• Transmits individual bits from one node to another.

Examples: Ethernet cables, hubs, and repeaters.

Common example of Layer 1 protocol:

Deals with the actual physical transmission of data over a network. Here are some common examples of Layer 1 protocols:

1. Ethernet:

- A widely used protocol for wired local area networks (LANs).

- Defines how data is transmitted over copper cables (e.g., Cat 5e, Cat 6) or fiber-optic cables.

- Ethernet frames include information like source and destination MAC addresses.

2. Wi-Fi (IEEE 802.11):

- Used for wireless communication within a local area network.

- Operates in the 2.4 GHz and 5 GHz frequency bands.

- Wi-Fi devices (such as routers and laptops) communicate using radio waves.

3. Bluetooth:

- Enables short-range wireless communication between devices (e.g., smartphones, headphones, keyboards).

- Commonly used for connecting peripherals or transferring files.

4. USB (Universal Serial Bus):

- Primarily used for connecting devices to a computer.

- Provides both power and data transfer.

- USB cables have different versions (e.g., USB 2.0, USB 3.0, USB-C).

These Layer 1 protocols handle the physical aspects of data transmission, ensuring reliable connectivity across networks!

2. Data Link Layer (Layer 2):

• Ensures error-free data transfer between nodes.
• Transmits packets using MAC addresses.

Examples: Network switches, NICs (Network Interface Cards).

Common example of Layer 2 protocol:

Plays a crucial role in managing data transmission within a local network. Here are some common examples of Layer 2 protocols:

1. Ethernet:

- Ethernet is widely used for wired local area networks (LANs).

- It defines how data is transmitted over copper cables (e.g., Cat 5e, Cat 6) or fiber-optic cables.

- Ethernet frames include information like source and destination MAC addresses.

2. Wi-Fi (IEEE 802.11):

- Wi-Fi is used for wireless communication within a local area network.

- It operates in the 2.4 GHz and 5 GHz frequency bands.

- Wi-Fi devices (such as routers and laptops) communicate using radio waves.

3. Bluetooth:

- Bluetooth enables short-range wireless communication between devices (e.g., smartphones, headphones, keyboards).

- Commonly used for connecting peripherals or transferring files.

4. LLDP (Link Layer Discovery Protocol):

- LLDP is vendor-neutral and commonly used as a component in network management and monitoring applications.

- It helps discover and exchange information about neighboring devices.

5. CDP (Cisco Discovery Protocol):

- CDP is a Cisco proprietary protocol that supports the IEEE 802.1ab version of LLDP.

- It primarily shares information between directly connected Cisco devices.

These Layer 2 protocols facilitate efficient communication within networks!

3. Network Layer (Layer 3):

• Provides logical addressing (IP addresses).
• Routes data between different networks.

Examples: Routers, IP packets.

Common example of Layer 3 protocol:

Is responsible for routing packets across interconnected networks. The most significant protocol at Layer 3 is the Internet Protocol (IP). Let's explore IP in more detail:

1. Internet Protocol (IP):

- IP uniquely identifies each device on the network.

- It transfers data from one node to another within the network.

- IP is a connectionless protocol, meaning it doesn't guarantee data delivery by itself. Higher-level protocols (such as TCP) ensure reliable transmission.

- There are two versions of IP: IPv4 (32-bit address scheme) and IPv6 (128-bit address scheme).

IP packets include source and destination IP addresses, allowing efficient routing across interconnected networks.

4. Transport Layer (Layer 4):

• Breaks data into smaller segments.
• Provides reliable (TCP) or unreliable (UDP) data delivery.

Examples: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

Common example of Layer 4 protocol:

Provides process-to-process communication for applications. Here are some common examples of Layer 4 protocols:

1. Transmission Control Protocol (TCP):

- TCP is widely used for connection-oriented transmissions.

- It ensures reliable data delivery, flow control, and error handling.

- Commonly used for web browsing, email, and file transfers.

2. User Datagram Protocol (UDP):

- UDP is used for simpler messaging transmissions.

- It is connectionless and does not guarantee data delivery.

- Commonly used for real-time applications (e.g., streaming, online gaming).

These Layer 4 protocols play a crucial role in efficient data transfer!

5. Session Layer (Layer 5):

• Establishes, maintains, and terminates sessions between applications.

Examples: Session management in video conferencing.

Common example of Layer 5 protocol:

Provides inter-process communication between two systems. It manages sessions between end-user application processes, facilitating a semi-permanent dialogue. Here are some common Layer 5 protocols:

1. AppleTalk Session Protocol (ASP):

- Used in AppleTalk networks for session management.

- Coordinates communication between applications.

- Ensures organized and synchronized data exchange.

2. AppleTalk Data Stream Protocol (ADSP):

- Also used in AppleTalk networks.

- Provides a reliable data stream between devices.

- Handles flow control and error recovery.

3. OSI Session Layer Protocol (X.225, ISO 8327):

- Part of the OSI protocol suite.

- Tries to recover connections after a loss.

- Provides synchronization points for message exchange.

4. Network Basic Input/Output System (NetBIOS):

- Used for communication between computers in a LAN.

- Provides services like name resolution and session establishment.

5. Password Authentication Protocol (PAP):

- Used for authentication during the session setup.

- Commonly used in dial-up connections.

6. Remote Procedure Call Protocol (RPC):

- Enables communication between distributed systems.

- Allows processes to invoke procedures on remote servers.

7. Point-to-Point Tunneling Protocol (PPTP):

- Creates virtual private networks (VPNs) over public networks.

- Establishes secure sessions for data transmission.

These protocols ensure efficient session management and communication!

6. Presentation Layer (Layer 6):

• Handles data encryption, compression, and formatting.

Examples: SSL/TLS for secure communication, data compression.

Common example of Layer 6 protocol:

Plays a crucial role in data exchange between different systems. It focuses on data formatting, encryption, and translation. Here are some common examples of Layer 6 protocols:

1. ASCII and EBCDIC Encoding:

- The presentation layer ensures that data can be represented in different character encodings.

- For example, converting an EBCDIC-coded text file to an ASCII-coded file.

2. XML (eXtensible Markup Language):

- XML is used for structuring and representing data.

- It standardizes complex data structures and facilitates interoperability.

3. Encryption/Decryption:

- Encryption is typically done at this layer.

- Decryption also occurs here (e.g., logging in to bank account sites).

4. Object Serialization:

- Complex data structures are serialized into flat byte-strings (e.g., using TLV or XML).

- Key functionality of the presentation layer.

Remember, the presentation layer ensures data compatibility and readability across different systems!

7. Application Layer (Layer 7):

• Provides an interface for user applications to access network services.

Examples: HTTP (web browsing), SMTP (email), FTP (file transfer).

Common example of Layer 7 protocol:

In the OSI model, plays a crucial role in network communication. It serves as the interface between users or processes and the network, providing application-specific services. Here are some common examples of Layer 7 protocols:

1. HTTP (Hypertext Transfer Protocol):

- Used for loading webpages and transmitting data between web browsers and servers.

- Responsible for fetching HTML, images, stylesheets, and other resources.

- Enables browsing the internet and interacting with websites.

2. SMTP (Simple Mail Transfer Protocol):

- Facilitates email communication.

- Responsible for sending and receiving emails between mail servers.

- Used by email clients (such as Outlook or Gmail) to send messages.

3. FTP (File Transfer Protocol):

- Used for transferring files between a client and a server.

- Allows users to upload, download, and manage files on remote servers.

- Commonly used for website maintenance and file sharing.

Layer 7 protocols enable meaningful communication between applications and users, making them essential for various network services!