Skip to main content

Networks and Internet

Subject: Computer Science
Topic: 3
Cambridge Code: 0478

Network Basics​

Network - Computers connected to share resources and data

Network Types​

LAN (Local Area Network):

  • Covers small area (building, campus)
  • High speed
  • Low latency
  • Usually owns equipment
  • Examples: School network, office LAN

WAN (Wide Area Network):

  • Covers large area (city, country, world)
  • Lower speed than LAN
  • Higher latency
  • Uses public infrastructure
  • Examples: Internet, banking networks

PAN (Personal Area Network):

  • Very small (personal devices)
  • Bluetooth, NFC
  • Short range

Network Hardware​

Network Interface Card (NIC)​

  • Enables computer to connect
  • Wireless (WiFi) or wired (Ethernet)
  • Unique MAC address

Switches​

  • Connect devices in LAN
  • Forward data to correct port
  • Faster than hubs
  • Learning bridges

Routers​

  • Connect networks
  • Forward packets between networks
  • Assign IP addresses (DHCP)
  • Network security (firewall)

Modems​

  • Modulation/demodulation
  • Convert digital to analog (upload)
  • Convert analog to digital (download)
  • ISP communication

Wireless Access Point​

  • WiFi transmission
  • Range: 30-100 meters
  • Shares network connection
  • Security: Encryption

TCP/IP Model​

TCP/IP - Foundation of internet communication

Four Layers​

Layer 1: Link Layer (Physical)

  • Hardware addressing
  • MAC addresses
  • Physical transmission
  • Ethernet frames

Layer 2: Internet Layer

  • Routing between networks
  • IP addresses
  • Logical addressing
  • IP protocol (IPv4, IPv6)

Layer 3: Transport Layer

  • End-to-end communication
  • TCP (reliable)
  • UDP (fast, unreliable)
  • Port numbers

Layer 4: Application Layer

  • Services to users
  • HTTP/HTTPS (web)
  • FTP (file transfer)
  • SMTP (email)
  • DNS (domain names)

IP Addressing​

IPv4 (Internet Protocol version 4)​

Format: 4 bytes (octets) separated by dots

Example: 192.168.1.100

Range: 0.0.0.0 to 255.255.255.255

Address classes:

  • Class A: 1-126 (large networks)
  • Class B: 128-191 (medium networks)
  • Class C: 192-223 (small networks)
  • Class D: 224+ (multicast)

Special addresses:

  • 127.0.0.1: Localhost
  • 192.168.x.x: Private
  • 255.255.255.255: Broadcast

IPv6 (Internet Protocol version 6)​

Format: 8 groups of 4 hex digits

Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334

Advantages:

  • Vastly larger address space
  • Simpler header
  • Built-in security (IPsec)
  • Better for IoT

Domain Names​

DNS (Domain Name System) - Translates domain names to IP addresses

Process:

  1. User enters URL (www.example.com)
  2. DNS query to DNS server
  3. Server returns IP address
  4. Browser connects to that IP

Components:

  • TLD: Top-level domain (.com, .org, .uk)
  • Domain: example.com
  • Subdomain: www, mail, ftp
  • FQDN: Fully qualified domain name

Communication Protocols​

HTTP/HTTPS​

HTTP (HyperText Transfer Protocol):

  • Stateless protocol
  • Web page delivery
  • Request-response model
  • Port 80

HTTPS (Secure HTTP):

  • Encrypted version
  • SSL/TLS encryption
  • Port 443
  • Certificates verify authenticity

FTP (File Transfer Protocol)​

  • File sharing
  • Upload/download
  • User authentication
  • Port 21

SMTP (Simple Mail Transfer Protocol)​

  • Email sending
  • Server-to-server
  • Port 25

POP3 / IMAP​

POP3:

  • Email retrieval
  • Deletes from server
  • Port 110

IMAP:

  • Email retrieval
  • Keeps on server
  • More flexible
  • Port 143

Wireless Networks​

WiFi (802.11)​

Standards:

  • 802.11b: 11 Mbps
  • 802.11g: 54 Mbps
  • 802.11n: 300 Mbps
  • 802.11ac: 1.3 Gbps
  • 802.11ax (WiFi 6): 9.6 Gbps

Range: 30-100 meters

Security: WPA/WPA2/WPA3 encryption

Bluetooth​

  • Short-range wireless
  • Personal area networks
  • Low power
  • Pairing required

Data Transmission​

Bandwidth vs Throughput​

Bandwidth:

  • Maximum capacity
  • Theoretical maximum
  • Measured in Mbps/Gbps

Throughput:

  • Actual data transfer rate
  • Usually less than bandwidth
  • Affected by interference, congestion

Packet Structure​

Packet - Data + headers

[Header: Source IP, Dest IP] [Data] [Trailer: Checksum]
  • Headers added at each layer
  • Stripped at destination
  • Ensures reliable delivery

Circuit vs Packet Switching​

Circuit switching:

  • Dedicated connection
  • Guaranteed bandwidth (phone)
  • Inefficient for data

Packet switching:

  • Shared connection
  • Variable bandwidth
  • Efficient for internet data

Network Topology​

Star Topology​

  • Central hub/switch
  • All devices connect to center
  • Failure of center fails network

Bus Topology​

  • Single cable backbone
  • Devices connected via taps
  • Collision domain issues

Ring Topology​

  • Devices in circle
  • Data travels one direction
  • Failure breaks network

Mesh Topology​

  • Fully or partially interconnected
  • Redundancy and reliability
  • Complex, expensive

Key Points​

  1. LAN: Local, high-speed; WAN: Wide area, lower speed
  2. TCP/IP has 4 layers
  3. IP addresses identify devices
  4. IPv4: 32-bit; IPv6: 128-bit
  5. DNS translates domain names
  6. HTTP/HTTPS: Web protocols
  7. WiFi: Wireless LAN standard
  8. Packet switching: Internet basis

Practice Questions​

  1. Distinguish LAN and WAN
  2. Explain TCP/IP model
  3. Convert IP addresses
  4. Describe DNS process
  5. Compare HTTP and HTTPS
  6. Explain WiFi standards
  7. Design network topology

Revision Tips​

  • Know network types clearly
  • Understand TCP/IP layers
  • Learn IP addressing
  • Know common protocols
  • Understand WiFi standards
  • Know OSI/TCP-IP model
  • Practice network design