Networking Models

How can computers from different organizations communicate with each other despite using different systems and technologies?

DefinitionNetwoking models

Categorise and provide a structure for Network Protocols and Standards

DefinitionNetworking protocols

Are a set of rules defining how network devices and software should work to connect and communicate to a network

Note

In the beginning the development of networks was chaotic.

  • Each vendor had its own proprietary solution.

  • The bad part was that one vendor’s solution was not compatible with another vendor’s solution.

This is where the idea for the standardized networking models such as OSI-model was born, having a layered approach to networks our hardware vendors would design hardware for the network, and others could develop software for the application layer.

Using an open model which everyone agrees on means we can build networks that are compatible with each other.

OSI (Open System Interconnection) Model

  • A conceptual architecture that standardizes the functions of a telecommunications or computer system into seven layers

  • Each layer has a number, name, functions and communicates with the layers directly above and below it

  • The first four layers are important for networking, while the upper three layers are important for applications.

  • The seven layers of this model, from the lowest (Layer 1) to the highest (Layer 7), are as follows:

    1. Physical Layer

      • Define physical characteristics of the used medium (voltage, connectors, . . . )

      • Convert digital bits to electrical or radio signals (encoding)

      • Bit transmission

    2. Data Link Layer

      • Provides node-to-node connectivity and data transfer

      • Define how data is formatted for transmission over a physical media

      • Error detection

      • Physical addressing

      • Two sublayers

        • Logical Link Control (LLC)

        • Media Access Control (MAC)

    3. Network Layer

      • Provide connectivity between end hosts in different networks

      • Logical addressing (IP)

      • Data routing and forwarding (routing protocols) between devices on different networks

    4. Transport Layer

      • Ensures reliable end-to-end communication

      • Split large data into smaller segments and handling error detection and correction

      • The most common transport layer protocols are:

        • TCP (Transmission Control Protocol) for reliable communications

        • UDP (User Datagram Protocol) for connectionless communications

    5. Session Layer

      • Establishes, maintains and terminates sessions or connections between applications on different devices

      • Provides synchronization and control mechanisms to ensure orderly data exchange

    6. Presentation Layer

      • Translates data between the application layer data and lower layers into appropriate format

      • Data encryption, decryption, compression and formatting

    7. Application Layer

      • The closest layer to the user interacting directly with end-user applications (web browser)

      • It provides network services directly to end-users or applications, and includes protocols such as HTTP, FTP, SMTP