Sieci komputerowe odc. 1 - Podstawy sieci

Introduction to Computer Networks

Overview of the Course

• Damian Stelmach introduces a new series of courses on computer networks aimed at students in IT and telecommunications fields, specifically for those preparing for qualifications E13, E15, and E16.

• The course content is designed not only for students but also for anyone interested in expanding their knowledge of computer networks.

Course Structure and Materials

• Each episode will include comprehensive descriptions, supplementary materials, and tests available through the website pasjainformatyki.pl.

• Emphasis is placed on engaging with all materials—videos, PDFs, exercises—to ensure thorough understanding.

Fundamentals of Computer Networks

Definition and Scope

• A computer network is defined as a connection between at least two computers for data exchange; this definition has evolved to include various devices like printers and mobile phones.

• Examples are provided showing everyday use of networks beyond computers, including gaming consoles and smart appliances like internet-connected refrigerators.

Key Concepts in Networking

• A computer network consists of devices such as computers, printers, phones, etc., connected to share data using transmission media.

• Important terms introduced:

• Host: A device assigned an IP address that can send/receive data.

• Server: A powerful computer providing services (e.g., web hosting).

• Client: Software or hardware that accesses services from a server.

Communication Protocols and Media

Transmission Elements

• Transmission media facilitate communication between devices; examples include copper cables, fiber optics, and radio waves used in Wi-Fi.

• Communication protocols define rules for data exchange; many will be discussed in future episodes focusing on ISO/OSI models and TCP/IP.

Internet vs. Intranet

• The internet is described as a global network of interconnected systems originating from ARPANET in the late 1960s.

• Distinctions are made between:

• Intranet: A private internal network using similar standards as the internet but restricted to authorized users (e.g., company employees).

• Extranet: An extension allowing access to external users (e.g., clients).

Domain Name System (DNS)

Functionality

• DNS translates user-friendly domain names into IP addresses necessary for locating resources on the internet.

This structured approach provides clarity on key concepts related to computer networks while ensuring easy navigation through timestamps linked directly to specific parts of the video.

Understanding Basic Networking Concepts

DNS and IP Addressing

• The Domain Name System (DNS) translates mnemonic names to IP addresses, a fundamental service of the Internet that converts website addresses like onet.pl into corresponding server IP addresses.

DHCP Protocol

• Dynamic Host Configuration Protocol (DHCP) automates network settings configuration by assigning IP addresses, subnet masks, and gateway addresses to hosts. This is crucial for managing large networks with potentially thousands of computers without manual configuration.

Data Transmission Units

• The course will cover basic networking concepts, with additional terms introduced as needed throughout the curriculum. A PDF file accompanying the course provides foundational knowledge in computer networking.

Data Size vs. Transmission Speed

• In computing, data size is typically measured in bits and bytes; however, in networking contexts, transmission speed is more critical than file size. Bandwidth indicates how much data can be transmitted over time, measured in bits per second rather than bytes.

Conversion Between Bits and Bytes

• Unlike file sizes which use bytes for measurement, network speeds are expressed in bits. Understanding this distinction is essential for converting between these units effectively.

Example Calculations

• One byte equals eight bits; thus, to convert from bytes to bits or vice versa involves simple multiplication or division by 8.

Practical Applications of Data Unit Conversion

Real-world Examples of Conversion

• To find out how many bits correspond to 100 bytes: multiply 100 by 8 resulting in 800 bits.

• For a file size of 2 MB converted to megabits: multiply by 8 yielding a total of 16 megabits.

Task Execution: Downloading Data Calculation

• To calculate data downloaded over one hour at a constant speed of 60 Mbit/s: convert hours to seconds (3600 seconds), then adjust speed from megabits to megabytes (7.5 MB/s), leading to approximately 26.3 GB downloaded.

Time Required for File Download

• For downloading a 1 GB file at a speed of 10 Mbit/s: first convert the download speed (1.25 MB/s), then divide the file size by this rate resulting in about 13 minutes and 39 seconds for completion.

Understanding Transmission Media in Computer Networks

Importance of Transmission Media

• The selection of appropriate transmission media is crucial for the effective and efficient operation of computer networks.

• Different types of wired media include copper media (coaxial cables and twisted pair cables) and fiber optic media, which are essential for network performance.

Coaxial Cables

• Coaxial cables, commonly referred to as "coax," consist of a copper core, plastic insulation, a copper shield, and an outer jacket. They end with a BNC connector.

• There are two types of coaxial cables: thin coax (5 mm thick) and thick coax (10 mm thick), with maximum lengths of 185 m and 500 m respectively.

• Both types support a maximum network bandwidth of 10 Mbit/s; however, coaxial cables are no longer used in new network constructions due to more efficient alternatives like twisted pair or fiber optics.

Twisted Pair Cables

• Twisted pair cables consist of eight copper wires twisted into four pairs, encased in an outer jacket, ending with an RJ45 connector (8P8C).

• There are three main types: UTP (unshielded twisted pair), FTP (shielded twisted pair), and STP (screened twisted pair), each providing varying levels of protection against electromagnetic interference.

Categories and Standards

• The choice of twisted pair cable depends on the environment's electromagnetic interference level and the intended application. UTP is commonly used in small LAN setups.

• Various categories exist for these cables—Category 3 through Category 7—each defining specific standards for Ethernet networks.

Technical Parameters

• Key technical parameters for twisted pair cables include signal attenuation measured in decibels, signal propagation expressed as a percentage, resistance measured in ohms, and the maximum bend radius which is typically four times its outer diameter.

Fiber Optic Cables: A Different Approach

Structure and Signal Type

• Unlike previous media that use copper conductors, fiber optic cables utilize glass fibers as their core material. This necessitates different signaling methods—light instead of electrical current.

Types of Fiber Optic Cables

• Basic fiber optic construction includes a core with a higher refractive index surrounded by cladding with a lower refractive index. Additional protective layers ensure durability during installation.

Connectors Used

• Fiber optic connectors differ significantly from those used in coaxial or twisted pair systems; common types include SC, LC, ST connectors among others.

Single-mode vs Multi-mode Fiber

• Fiber optics can be categorized into single-mode fibers that transmit one light beam over long distances without signal degradation versus multi-mode fibers that carry multiple beams but suffer from greater signal dispersion over distance.

Applications Based on Distance

• Single-mode fibers allow long-distance communication without amplification devices while multi-mode fibers are suitable for shorter distances up to several kilometers due to increased signal dispersion caused by multiple light paths within the core.

Overview of Transmission Media: Copper vs. Fiber Optics

Advantages and Disadvantages of Copper Media

• Copper media, such as twisted pair cables, are cost-effective for both cable and networking equipment.

• They are easy to install and diagnose, with affordable tools available for maintenance.

• However, copper media are sensitive to electromagnetic interference (EMI), limiting their effective range to a maximum of 100 meters.

• Additionally, copper has lower bandwidth compared to fiber optics.

Advantages and Disadvantages of Fiber Optic Media

• Fiber optic media offer high bandwidth capabilities and can transmit data over long distances with minimal signal degradation.

• They are less susceptible to electromagnetic interference compared to copper cables.

• The downsides include signal dispersion issues and the need for specialized installation tools, making them more expensive than copper solutions.

Wireless Transmission Media: Wi-Fi Technology

Characteristics of Wireless Networks

• Wireless networks primarily use radio waves for data transmission, operating within frequencies from 3 Hz to 3 THz.

• Sources of radio waves can be natural or artificial, such as those emitted by mobile phone towers.

• For wireless LAN (Local Area Network), two frequency bands are commonly used: 2.4 GHz and 5 GHz.

Types of Computer Networks Based on Area

Classification by Geographic Scope

• Networks can be categorized based on their operational area:

• LAN (Local Area Network): Smallest network type found in homes or schools.

• MAN (Metropolitan Area Network): Covers larger areas like cities or urban regions.

• WAN (Wide Area Network): Comprises interconnected LAN and MAN networks across broader geographical areas.

Architectural Classifications

• Networks can also be classified by architecture into:

• Client-server architecture: Involves one or more servers providing services to multiple clients (e.g., web browsing).

• Peer-to-peer architecture: All computers have equal status; each can share resources without a central server.

Understanding Network Topologies

Definition and Importance

• Network topology refers to the arrangement of devices in a network, defining how they connect and communicate with each other.

Types of Topologies

Physical vs. Logical Topology

• Physical topology describes the actual layout of devices in the network.

• Logical topology outlines how data flows between devices regardless of physical connections.

Basic Topologies

1. Bus Topology

• All devices connect to a single communication line; historically used coaxial cables but suffers from low bandwidth limitations (~10 Mbps).

• Vulnerable to failures; if the main cable fails, the entire network goes down.

2. Ring Topology

• Each device connects directly to two others forming a closed loop; allows various transmission media but is prone to failure if any connection breaks unless using dual-ring configurations for redundancy.

Topologie sieci komputerowych

Topologia gwiazdy

• Topologia gwiazdy polega na podłączeniu urządzeń do centralnego punktu, który pełni rolę dostępu do sieci. W przeszłości używano koncentratorów (hub), obecnie stosuje się przełączniki (switch).

• Jest to najczęściej spotykana topologia w lokalnych sieciach komputerowych ze względu na prostotę projektowania, budowy oraz rozbudowy.

• Topologia ta jest odporna na awarie i łatwa w zarządzaniu, co czyni ją preferowaną opcją dla wielu zastosowań.

• Możliwe jest wykorzystanie różnych mediów transmisyjnych, takich jak skrętka miedziana, kabel światłowodowy czy fale radiowe.

• Główną wadą tej topologii są koszty budowy związane z dodatkowymi urządzeniami i kablami.

Topologie logiczne

• Logiczną topologię definiują sposoby oraz reguły komunikacji urządzeń w sieci. Wyróżnia się trzy główne typy: punkt-punkt, pierścień oraz wielodostępowa.

Topologia punkt-punkt

• W topologii punkt-punkt dane przesyłane są bezpośrednio między dwoma urządzeniami. Mogą być one połączone bezpośrednio lub za pomocą urządzeń pośredniczących.

Topologia pierścienia

• W tej topologii dane przekazywane są kolejno przez wszystkie urządzenia w sieci. Każde urządzenie analizuje otrzymane dane i decyduje o ich dalszym przesyłaniu.

Topologia wielodostępowa

• Umożliwia komunikację poprzez jedno fizyczne medium transmisyjne. Wszystkie urządzenia "widzą" dane przesyłane przez sieć, ale tylko adresowane do nich interpretują te informacje.

Mechanizmy kontrolujące dostęp do medium

• Aby umożliwić współdzielenie medium transmisyjnego, wprowadzono mechanizmy takie jak CSMA/CD (Carrier Sense Multiple Access with Collision Detection), CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), oraz token passing.

Metoda CSMA/CD

• Polega na nasłuchiwaniu stanu łącza przed rozpoczęciem transmisji. Jeśli łącze jest wolne, transmisja może się rozpocząć; w przypadku kolizji następuje przerwa i ponowna próba.

Metoda CSMA/CA

• Również opiera się na nasłuchiwaniu, ale przed rozpoczęciem transmisji wysyła informację o zamiarze jej rozpoczęcia. Często stosowana w sieciach bezprzewodowych.

Metoda token passing

• Polega na przesyłaniu specjalnej porcji danych zwanej żetonem (token). Posiadanie żetonu uprawnia do rozpoczęcia transmisji.

Podsumowanie

• Omówiono różnorodne aspekty dotyczące topologii sieci komputerowych oraz mechanizmów kontrolujących dostęp do medium.