Computer Networks: PAN, LAN, MAN and WAN

• Computer networks are interconnected devices that share data and resources.
• Networks facilitate file sharing, communication, and internet access.

Types of Networks

• Personal Area Network (PAN): A small network up to 10 meters, like Bluetooth devices, wireless keyboards, and smartwatches.
• Local Area Network (LAN): Confined to a building or campus, found in offices, schools and Ethernet-based.
• Metropolitan Area Network (MAN): Spans a city, connecting multiple LANs, such as citywide Wi-Fi and cable TV networks.
• Wide Area Network (WAN): Covers a large geographic area, even countries. The Internet is the largest WAN.
• Internetwork: Networks communicate with each other, forming the global internet.

Internet, Intranet, and Extranet

• Internet: A global public network for communication and information sharing.
• Intranet: A private internal network for employees.
• Extranet: A private network allowing controlled access to external parties.

Networking Devices

• Hub: Broadcasts data to all connected devices.
• Switch: Sends data to specific devices using MAC addresses.
• Router: Routes packets between different networks using IP addresses.
• Bridge: Connects two LANs.
• Access Point: Provides wireless connectivity.

Data Communication Elements

• Message: Information being sent.
• Sender: Device transmitting the message.
• Receiver: Device receiving the message.
• Transmission Medium: The communication path.
• Protocols: Rules ensuring proper communication, like TCP/IP.

Effective Data Communication essential characteristics

• Delivery: Data must reach the correct recipient.
• Accuracy: Received data must be error-free.
• Timeliness: Data should arrive without delays, ensuring real-time communication.
• Jitter: Variation in delay between packet arrivals, crucial for audio/video streaming.

Data Representation Techniques

• Text: Represented in binary using ASCII or Unicode (e.g., 'A' in ASCII → 01000001).
• Number: Numeric data converted into binary (e.g., Decimal 10 → 1010).
• Image: Stored as pixels in formats like JPEG or PNG.
• Audio: Analog signals converted to digital using Pulse Code Modulation (PCM) with audio wave sampled at regular intervals.
• Video: Sequence of images (frames) displayed at a specific rate (e.g., 30 FPS).

Signal Types

• Analog Signals: Continuous waveforms used in AM/FM radio, like sine waves.
• Digital Signals: Represent binary data (0s and 1s) as discrete pulses, like square waves.

Digital Conversion

• Line Coding: Converts binary data to signals; types include Unipolar, Polar, and Bipolar.
  • Unipolar: Uses only positive voltages.
  • Polar: Uses positive and negative voltages.
  • Bipolar: Alternates polarities for 1s.
• PCM (Pulse Code Modulation): Converts analog signals to digital using sampling, quantization, and encoding.

Transmission Modes

• Parallel Transmission: Sends multiple bits simultaneously.
• Serial Transmission: Sends bits one by one.
• Multiplexing: Combines multiple signals into one; includes FDM, TDM and WDM.
  • FDM (Frequency Division Multiplexing): Divides channels by frequency.
  • TDM (Time Division Multiplexing): Divides channels by time slots.
  • WDM (Wavelength Division Multiplexing): Used in fiber optics.

Communication Modes

• Simplex: One-way communication.
• Half-Duplex: Data flows both ways, but one direction at a time.
• Full-Duplex: Simultaneous two-way communication.

Transmission Media

• Guided (Wired):
  • Twisted Pair Cable: commonly used in LANs.
  • Coaxial Cable: Used in cable TV and dated networks.
  • Fiber Optics: High-speed data transfer using light.
• Unguided (Wireless):
  • Radio Waves: Wi-Fi and long-range communication.
  • Microwaves: Satellite communication.
  • Infrared: Short-range communication like remote controls.

Transmission Impairments

• Transmission impairments degrade the quality of communication signals.
• Attenuation: Signal weakens with distance, solved using amplifiers or repeaters.
• Delay Distortion: Signal components arrive at different times, rectified using equalizers.
• Noise: Unwanted signals interfere with the message.
  • Thermal Noise: Heat in components.
  • Crosstalk: Interference from nearby communication lines.
  • Impulse Noise: Bursts caused by lightning or faults.

Protocols

• Protocols:
  • HTTP/HTTPS: Web browsing.
  • SMTP: Sending emails.
  • FTP: Transferring files.
  • DNS: Converts domain names to IP addresses.
  • DHCP: Automatically assigns IP addresses.
  • Telnet: Provides remote access to devices.

Standards

• De Facto: Unofficial but widely adopted standards.
• De Jure: Officially approved standards.

Switching Techniques

• Circuit Switching: Dedicated path established before transmission.
  • Advantage: Reliable with low latency.
  • Disadvantage: Inefficient resource usage.
• Packet Switching: Data divided into packets transmitted independently.
  • Advantages: Efficient and scalable.
  • Disadvantages: Potential latency and packet loss.

Error Detection and Correction

• Parity Check: Detection by adding a bit to indicate parity.
• CRC (Cyclic Redundancy Check): Detection using polynomial division.
• Backward Error Correction: Correction by requesting retransmission of corrupted packets.
• Forward Error Correction: Correction by automatically correcting errors using abundant data.

Network Performance

• Bandwidth: Maximum data transfer rate (bits per second).
• Latency: Delay in data transfer (milliseconds).

Security Mechanisms

• Firewalls: Block unauthorized access.
• IDS/IPS (Intrusion Detection/Prevention Systems): Detect and prevent malicious activities.

Common Protocols and Their Ports

• HTTP (80): Web browsing.
• HTTPS (443): Secure web browsing.
• FTP (21): File transfers.
• SMTP (25): Email sending.
• DNS (53): Domain name resolution.
• DHCP (67/68): Dynamic IP assignment.

OSI and TCP/IP Models

• OSI Model:
  • Physical Layer: Hardware connections and transmission.
  • Data Link Layer: Error detection and framing.
  • Network Layer: IP addressing and routing.
  • Transport Layer: Reliable data delivery.
  • Session Layer: Manages sessions between devices.
  • Presentation Layer: Data translation and encryption.
  • Application Layer: Services to users.
• TCP/IP Model:
  • Network Interface: Combines physical and datalink layer functions.
  • Internet: Handles routing and IP addressing.
• Transport: Reliable delivery using TCP or UDP.
• Application: Combines OSI session, presentation, applications layers.

Computer Network Topologies

• Point-to-Point: Two devices connected directly.
• Bus: Devices share a single line, simple but failure-prone.
• Star: Devices connect to a central hub; hub failure affects all.
• Ring: Devices form a closed loop; one connection failure affects the network.
• Mesh: Every device connects to every other; reliable but expensive.
• Hybrid: Combination of different topologies.

IP Address Classes

• Class A: 1-127 (127 is reserved for loopback).
• Class B: 128-191.
• Class C: 192-223.
• Class D: 224-239 (Multicast).
• Class E: 240-255 (Experimental).

Private Address Space

• Class A: 10.0.0.0 to 10.255.255.255
• Class B: 172.16.0.0 to 172.31.255.255
• Class C: 192.168.0.0 to 192.168.255.255

Default Subnet Masks

• Class A: 255.0.0.0
• Class B: 255.255.0.0
• Class C: 255.255.255.0
• Subnetting divides networks into smaller more secure and efficient parts
• Subnet Mask defines the network and host portions of IP addresses

CMD Commands for Networking

• Ping: Tests connectivity.
• Ipconfig: Displays IP address, subnet mask, and default gateway.
• Tracert: Traces the route packets take.
• Nslookup: Resolves domain names to IP addresses.
• Netstat: Displays active connections and network statistics.
• Arp -a: Displays the ARP table for IP-to-MAC address mapping.
• Msconfig: Configures computer startup programs and services.