Основы организации компьютерных сетей | Курс "Компьютерные сети"

Introduction to Computer Networks

In this section, the lecturer introduces the basics of organizing computer networks. The challenges of building large networks and the need for reliability, scalability, and security are discussed. The concept of network decomposition into layers is introduced.

Basics of Organizing Computer Networks

• Building a small network connecting two computers on a desk is simple, but building a large network that connects all computers in the world is much more complex.

• Large networks require careful consideration of diverse equipment and software that will be connected to the network.

• A network should be reliable and continue functioning even if some devices fail.

• The ability to expand the network by adding new computers or connecting existing ones is important.

• It is impossible to build a network with enough resources to connect all users simultaneously, so resource allocation becomes crucial.

• Quality of service needs to be ensured for different types of data transmission, such as low latency for voice communication or high speed for file transfers.

• Security is essential to protect against theft or unauthorized access to personal and organizational data.

Network Decomposition into Layers

• Building a computer network is a complex task that can be simplified using decomposition techniques.

• Decomposition involves breaking down a complex problem into simpler tasks that can be individually solved.

• Computer networks are organized into layers, where each layer solves specific tasks related to communication between devices.

• Each layer provides services to the layer above it while utilizing services from the layer below it.

• This layered approach allows for isolation and modularity in designing and implementing networks.

• Changes in one layer do not require modifications in all other layers; only the affected layer needs adjustment.

Levels in Computer Network Organization

This section explains how computer networks are organized into levels or layers. Each level addresses specific tasks and responsibilities, allowing for a modular and scalable network design.

Levels in Computer Network Organization

• Computer networks are organized into levels or layers to address different tasks and responsibilities.

• Each level is responsible for solving specific problems related to communication between devices.

• The lowest level, the physical layer, deals with transmitting data over the physical medium without understanding its content.

• Higher levels build upon lower levels, providing more complex services such as routing in a composite network.

• Separating functionality into layers allows for easier management and troubleshooting of networks.

• Changes or upgrades can be made at specific layers without affecting the entire network infrastructure.

Services, Interfaces, and Protocols

This section explains the concepts of services, interfaces, and protocols in computer networks. It highlights their importance in enabling communication between different levels of a network.

Services, Interfaces, and Protocols

• Services are functions provided by each level of a network to the layer above it. They define what tasks a level can perform.

• Interfaces are sets of operations that allow one level to interact with another level. They provide access to services offered by lower levels.

• Protocols are rules and agreements used for communication between two levels. They define how data is exchanged between them.

• Separating services from interfaces and protocols allows for flexibility in designing networks.

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Network Architecture and Levels

This section discusses the concept of network architecture and levels, as well as their distribution. It also introduces the idea of protocol stacks and standard models for organizing networks.

Understanding Network Architecture

• Network architecture determines the levels and functions within a network.

• The distribution of functions across different levels is defined by the network's architecture.

• Interfaces are not included in the architecture as they can vary on different platforms.

Protocol Stacks and Standard Models

• A protocol stack is a hierarchical set of protocols used for network communication.

• Various network architectures can be designed based on specific requirements.

• To build large networks that can connect with each other, adherence to standardized network organization is necessary.

• Standard models for network organization are called reference models.

• Two popular reference models are OSI (Open Systems Interconnection) model and TCP/IP (Transmission Control Protocol/Internet Protocol) model.

OSI Model and TCP/IP Model

This section provides an overview of two popular reference models - OSI model and TCP/IP model - which define the structure and functionality of networks.

OSI Model

• The OSI model consists of seven layers that define various protocols used in networking.

• It was the first model to separate service, interface, and protocol concepts.

• However, it is not widely used in practice.

TCP/IP Model

• The TCP/IP model is based on the popular TCP/IP protocol stack.

• It consists of four layers that focus primarily on protocols widely used in practical networking scenarios.

• The protocols within this model form the foundation of the internet.

Encapsulation in Networking

This section explains encapsulation, which involves including messages from higher-level protocols within messages from lower-level protocols.

Encapsulation Process

• Messages in a network transmission consist of three parts: header, data, and trailer.

• Encapsulation involves adding headers from lower-level protocols to messages from higher-level protocols.

• In a hypothetical network with three levels, the third level forms the message and passes it to the second level.

• The second level divides the message into smaller parts and adds its own header.

• The first level then adds its header and combines the two messages into one large message before passing it on to the third level.

Decomposition and Layered Approach

This section discusses decomposition and the layered approach in network organization, where complex tasks are divided into simpler parts using a template of levels.

Decomposition in Networking

• Complex networking tasks are decomposed into simpler parts for easier resolution.

• Each level in a network performs one or more related tasks that are relatively simple to solve.

• Levels provide services to higher levels, which handle more complex tasks.

Important Concepts in Network Organization

• Service: Describes what a particular level does.

• Protocol: Specifies how a particular level operates.

• Interface: Defines how to access a service provided by a level.

Building Networks Practically

This section emphasizes practical considerations when building networks, including services provided by each level, protocols used, and accessing those services through interfaces.

Practical Network Construction

• When constructing networks practically:

• Consider the services provided by each level.

• Understand how each protocol operates within its respective level.

• Know how to access services through interfaces.