OSI and TCP/IP Models

• Computer network models are the models implemented using models in computer networks.

Introduction

• Data communication between two or more users requires a systematic approach for transmitting data.
• This approach enables users to communicate and transmit data through an efficient and ordered path.

Network Models

• The two primary network models are the OSI Model and the TCP/IP Model.

OSI Model

• The OSI (Open Systems Interconnection) Model is a 7-layered conceptual framework describing the functions of a networking system.
• It was established by Jack Holdsworth of the International Organization for Standardization (ISO) in the late 1970s.
• It characterizes computing functions into rules and requirements for interoperability.
• The layers are:
  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data Link
  • Physical

Physical Layer

• The Physical Layer residing at the bottom-most position in the OSI model, associates with the electrical, mechanical and functional parts of transmission media for information transmission over the internet.
• It deals with physical devices for data communication, including cable types and transmission modes like Simplex, Half Duplex, and Full Duplex.
• It determines the topology of any network, forming the fundamental structure.
• The core function involves transmitting and receiving bits in the form of 1 & 0 (Binary Value).
• Additional features encompass defining and managing synchronization, physical topologies, bandwidth, rate of transmission, and data channel.
• Devices at this layer include transmission cables, repeaters, hubs, transmitters, and receivers.

Data Link Layer

• The Data Link Layer acts as an intermediate layer responsible for ensuring delivery of data to its destination in the network using the physical address known as MAC (Media Access Control) Address.
• Data-Link Layer assembles the data message into special structures called data frames, which contain the source address field, destination address fields, and the data message.
• It is subdivided into two fields: Logical Link Control & Media Access Control.
• Logical Link Control establishes and maintains communication links between devices.
• Media Access Control maintains the physical addresses of the sender and receiver for reliable data packet delivery.
• The main function is to synchronize data and ensure the proper delivery of data messages from sender and receiver.
• Devices include switches, Ethernet, and Frames.

Network Layer

• It is responsible for establishing data communication channels between multiple networks, nodes, devices, or hosts.
• A network layer is needed when a connection must be established between two or more networks; It is not required if devices are locally connected.
• A major role is en-routing data packets from source to destination over different networks through routers.
• Logical addressing for all devices is provided via the Internet Protocol (IP) Address.
• Devices include Routers and Gateway devices

Transport Layer

• The Transport Layer is the middle (4th) layer of the OSI Model, acting as the transition point between upper and lower layer functions.
• It facilitates connection-oriented service (using TCP) and connection-less service (using UDP).
• Devices include Network devices, gateway devices, and ports.

Session Layer

• The Session Layer maintains sessions between users and software where users interact.
• It deals with the establishment and management of sessions among applications, and keeps user data separate.
• Connection establishment and termination are key features.

Presentation Layer

• The presentation layer's role is to appropriately represent data through various data presentation techniques.
• It ensures that data is presented in the same format at both the sender's and receiver's ends.
• It facilitates data translation among different devices ensuring data is similarly presented across devices, irrespective of the devices used.

Application Layer

• The Application Layer is the topmost layer.
• It provides an interface among users and software applications.
• Functions as the front-end layer for user communication, while other layers operate in the back-end.
• Examples of application interactions include file transfer, emails, and remote access.
• Key features: proper UI/UX of software and identifying communication users/partners.

TCP/IP Model

• Transmission Control Protocol/Internet Protocol has a layered architecture which allows data communication along with the integration of protocols.
• Layout is like the OSI Model however only 4 layers exist.
• These include:
  • Network Access Layer
  • Internet Layer
  • Transport Layer
  • Application Layer
• The Network Access Layer is responsible for the Physical Layer and Data Link Layer.
• Data received as bits connects as data packets to the Internet Layer.
• The Internet Layer (also called Network Layer) establishes connections for data packets between users/devices/networks, being the 2nd layer from the bottom.
• The Transport Layer has a similar function to the OSI model as it provides similar features, and offers end-to-end transfer using connection-oriented services.
• The Application Layer interfaces users and applications like the OSI Model.
• The Application layer functionality can perform session and presentation layer functions.

Advantages of the OSI Model

• Each layer has a definite structure which makes the OSI model easy to use.
• It is a general-purpose reference model for data communication.
• The OSI Model supports connection-oriented and connection-less services, and connections between various devices are possible.

Disadvantages of the OSI Model

• The model has limitations due to its inability to fit protocols.
• Session and presentation layers may not provide high and functions compared to other layers.

Advantages of the TCP/IP Model

• It uses protocol implementation and has protocol support.
• Each layer has structure, making it simple to use like OSI model.
• Utilized a layered architecture.

Disadvantages of the TCP/IP model

• Some layers may have numerous functions
• If something happens to these protocols that the reference model is unable to handle, it may cause difficulty.

Similarities Between the OSI and TCP/IP Models

• Both models have layered architecture, compare layers, and define protocols in a layer-wise manner.
• The physical and data link layers of the OSI model are similar with the link layer to the TCP/IP model.
• The network and transport layers are alike in both.
• The application layer of the OSI model is similar to the session, presentation and application layer of the TCP/IP model.

Differences Between the OSI and TCP/IP Models

• The OSI model is generic, while TCP/IP is protocol-oriented. The OSI model are guidelines of communication, the TCP/IP model contains specifications to how to complete the communication.
• The OSI model was developed before its protocols, whereas the TCP/IP model had protocols that were made prior.

Explore the OSI and TCP/IP models, fundamental frameworks for understanding network communication. Learn about the layers, their functions, and how they relate to each other. Understand the key protocols and standards that govern data transmission across networks.