Lec-2: Introduction to Computer Network | OSI MODEL in easiest Way in Hindi | Need of OSI model

Understanding Computer Networks

Overview of Computer Networks

• A computer network consists of various computing devices that connect to share data. The primary purpose is data sharing among homogeneous and heterogeneous devices.

• Communication in a network involves a sender and a receiver, where the sender transmits data to the receiver, which can be either machines or users.

Data Transmission Process

• Data transmission requires a connection, which can be wired or wireless. This connection facilitates the movement of packets from the sender to the receiver.

• When a message (e.g., "M") is sent by the sender, it must be received and understood by the receiver ("R"). Understanding depends on protocols running on both ends.

Importance of Protocols

• Protocols are sets of instructions that ensure data sent by the sender can be comprehended by the receiver. Without mutual understanding facilitated by protocols, communication fails.

• An analogy is drawn with language barriers; if two people speak different languages, they may hear each other but not understand without a common protocol (language).

Client and Server Dynamics

• In networking terms, senders and receivers are often referred to as clients and servers. They may exist on separate machines or within the same machine contextually for inter-process communication (IPC).

• IPC occurs when processes communicate within one machine (e.g., keyboard input displayed on monitor), while computer networks involve distinct machines communicating over distances.

Distinction Between IPC and Networking

• The operating system manages IPC through its kernel; however, this does not fall under computer networking's scope unless clients and servers are on different machines. Thus, networking concepts arise when client-server pairs are physically separated across different locations.

Understanding Computer Networks and Their Functionality

Introduction to Computer Networks

• The concept of computer networks is introduced, explaining the interaction between machines in different locations (e.g., India and USA).

• Everyday applications like Google and Facebook are highlighted as common examples of network usage, emphasizing their ubiquity in daily life.

• The process of sending messages from a user's machine to a server (e.g., Facebook's server in the USA) is described, illustrating the communication flow.

User Experience and Data Access

• Users experience fast data access that feels instantaneous, akin to accessing files on a local hard drive.

• The abstraction provided by computer networks allows users to interact with remote servers without awareness of their physical locations.

• The main function of computer networks is to create an environment where client-server processes feel co-located despite being physically separated.

Communication Between Client and Server

• Two-way communication is essential; when a user requests data from a server, the server must respond appropriately.

• There are two types of functionalities involved in this communication: mandatory and optional.

Mandatory Functionalities

Error Control

• Error control ensures that messages sent from one machine are received accurately by another, addressing potential issues like noise or hacking.

• It’s crucial for systems to detect errors during transmission so that corrective actions can be taken if necessary.

Flow Control

• Flow control manages the amount of data sent over the network to prevent congestion and ensure smooth operation.

• Protocol mechanisms help maintain proper data flow without overwhelming system resources.

Multiplexing and Demultiplexing

• These processes allow multiple programs on a machine to send and receive data simultaneously while managing which process handles specific communications.

Optional Functionalities

Cryptography

Understanding Encryption and the OSI Model

The Role of Encryption in Applications

• Not all applications require encryption; however, banking applications necessitate it for secure money transfers to prevent data breaches.

• Implementing optional coding functions increases system complexity and can slow down data transmission, highlighting the need for balance between security and efficiency.

Data Transmission Protocols

• Using normal HTTP does not require encryption, but HTTPS encrypts data during transmission, emphasizing the importance of security in certain contexts.

• Checkpoints are crucial when downloading large files; they allow resuming downloads from a specific point rather than starting over if a failure occurs.

Application-Specific Needs

• For small data transmissions (e.g., WhatsApp messages), checkpoints may be unnecessary as adding such functionalities could complicate the system without significant benefits.

Introduction to the OSI Model

• The discussion transitions to the OSI model, which encompasses over 70 functionalities categorized into mandatory and optional layers.

• The OSI model serves as a theoretical framework that standardizes how data is sent and received across networks, ensuring consistency in communication protocols.

Structure of the OSI Model

• The OSI model consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has distinct functionalities contributing to overall network communication.

• When sending messages through this model, each message passes through all seven layers to ensure proper handling according to established protocols.

Comparison with Other Models