Networks Including The Internet (Copy)
Cheat Sheet: A Level Computer Science – Networks, Transmission & Internet
1. Networking Devices – Purpose & Benefits
| Device | Function |
|---|---|
| Switch | Connects devices on a LAN and intelligently forwards data to the correct device |
| Server | Provides services (e.g. file, web, email) to clients in a network |
| NIC / WNIC | Network Interface Card connects a device to a wired or wireless network |
| Wireless Access Point (WAP) | Allows wireless devices to connect to a wired network |
| Router | Forwards data between networks; often connects LAN to the internet |
| Bridge | Connects two network segments, forwarding based on MAC addresses |
| Repeater | Regenerates and amplifies signals to extend network range |
2. LAN vs WAN
| LAN | WAN |
|---|---|
| Covers small geographical area | Covers large geographical area |
| Owned by organisation | Uses shared/public infrastructure |
| Higher speed, lower latency | Slower speed, higher latency |
| E.g., school, office | E.g., internet |
3. Client-Server vs Peer-to-Peer (P2P)
| Feature | Client-Server | Peer-to-Peer |
|---|---|---|
| Control | Centralized | Decentralized |
| Security | Easier to manage | Difficult to manage |
| Scalability | Easily scalable | Not ideal for large networks |
| Cost | Higher (needs servers) | Lower (no dedicated server) |
| Use When | High security, centralized resources needed | Small networks with file sharing |
Roles of Computers:
- Client: Requests services
- Server: Provides resources (files, authentication, web)
- Peer (P2P): Acts as both client and server
4. Thin-Client vs Thick-Client
| Feature | Thin-Client | Thick-Client |
|---|---|---|
| Processing | On server | On client |
| Cost | Lower | Higher |
| Performance | Slower (relies on network) | Faster (local processing) |
| Security | Centralized control | Harder to manage |
| Use Case | Web terminals, schools | Personal laptops, offices |
5. Network Topologies
| Topology | Features | Use When |
|---|---|---|
| Bus | Shared backbone cable; collisions possible | Small temporary setups |
| Star | All devices connect to central switch/hub | Common LANs; easy to manage |
| Mesh | Devices interconnect; redundant paths | High reliability needed (e.g., military) |
| Hybrid | Mix of topologies | Large or custom networks |
Packet Transmission:
- In star, central device handles all traffic
- In mesh, multiple routes exist
- Bus uses CSMA/CD to detect collisions
6. Cloud Computing
| Type | Features |
|---|---|
| Public Cloud | Services over the internet (e.g., Google Drive) |
| Private Cloud | Dedicated for one organization, more control and security |
| Benefits | Drawbacks |
|---|---|
| Scalability | Internet dependence |
| Accessibility | Security concerns |
| Cost-effective | Data ownership ambiguity |
7. Wired vs Wireless Networks
| Wired | Wireless |
|---|---|
| Stable & faster | Convenient & mobile |
| Higher security | Vulnerable to interception |
| Requires cabling | Susceptible to interference |
8. Transmission Media
| Medium | Features |
|---|---|
| Copper Cable | Cheap, short distance, signal loss |
| Fibre-Optic | High speed, long distance, expensive |
| Radio Waves (WiFi) | Wireless, short range, affected by walls |
| Microwaves | Line-of-sight, medium-long range |
| Satellites | Very long range, high latency, expensive |
9. Ethernet & CSMA/CD
- Ethernet: Standard for LANs using wired communication
- CSMA/CD (Carrier Sense Multiple Access/Collision Detection):
- Device listens before transmitting
- If collision detected, it waits a random time and retries
- Reduces packet collision in shared media
10. Bit Streaming
| Type | Explanation |
|---|---|
| Real-time | Data sent and played immediately (e.g., live sports) |
| On-demand | Data buffered and played later (e.g., Netflix) |
Bit Rate Impact:
- Higher bitrate = better quality + larger file size
- Broadband speed affects playback quality and buffering
11. Internet vs World Wide Web (WWW)
| Internet | WWW |
|---|---|
| Physical network infrastructure | Collection of webpages accessed via internet |
| Includes servers, routers, cables | Uses HTTP/HTTPS protocols |
| Broader term | Subset of internet |
12. Internet Hardware
| Device | Function |
|---|---|
| Modem | Modulates and demodulates analog signals for internet access |
| PSTN | Traditional telephone lines used for dial-up connections |
| Dedicated Lines | High-speed, always-on internet connection (e.g., leased lines) |
| Cell Phone Network | Provides mobile internet using towers and satellites |
Cheat Sheet: A Level Computer Science – IP Addresses, Subnetting, and URL Resolution
1. IP Address and Data Transmission
What is an IP Address?
- A unique identifier assigned to each device on a network.
- Used to route data to the correct destination.
2. IP Address Formats
| Version | Format | Example |
|---|---|---|
| IPv4 | 32-bit, written as 4 decimal numbers separated by dots | 192.168.1.1 |
| IPv6 | 128-bit, written as 8 groups of 4 hexadecimal digits | 2001:0db8:85a3:0000:0000:8a2e:0370:7334 |
- IPv4 allows ~4.3 billion addresses.
- IPv6 allows ~340 undecillion addresses (solution to IPv4 exhaustion).
3. Subnetting
- Purpose: Divides a network into smaller sub-networks (subnets).
- Benefits:
- Improves network efficiency and security.
- Limits broadcast traffic.
- Subnet mask: Used with the IP address to determine the network and host portions.
- Example: IP = 192.168.1.25, Subnet mask = 255.255.255.0
4. Association of IP with a Device
- Assigned by DHCP (Dynamic Host Configuration Protocol) or manually.
- Can be static (permanently assigned) or dynamic (changes over time).
5. Public vs Private IP Addresses
| Type | Usage | Security Implications |
|---|---|---|
| Public IP | Used on internet-facing devices | Exposed to internet; needs firewall/security |
| Private IP | Used within local networks | Hidden from internet; needs NAT to access web |
- Private Ranges (IPv4):
- 10.0.0.0 – 10.255.255.255
- 172.16.0.0 – 172.31.255.255
- 192.168.0.0 – 192.168.255.255
6. Static vs Dynamic IP Addresses
| Type | Assigned | Use Case | Pros/Cons |
|---|---|---|---|
| Static | Manually | Servers, printers, DNS | Consistent, but less secure and harder to manage |
| Dynamic | DHCP | General user devices | Easier to manage, changes over time |
7. URL and DNS
Uniform Resource Locator (URL)
Structure Example:
https://www.example.com/index.html
| Component | Function |
|---|---|
| https | Protocol used to access the resource |
| www.example.com | Domain name |
| /index.html | Path to specific file or resource |
Domain Name Service (DNS)
- Translates human-readable domain names into IP addresses.
- E.g.,
www.example.com→93.184.216.34 - Acts like a phonebook for the internet.
- Recursive and authoritative servers involved in resolving a domain.
- Reduces need to remember IPs, supports dynamic changes to servers.