Notes › Chapter 2
Chapter 2 · Paper 1
Communication
Networks, topologies, the internet, IP addressing, DNS, and everything about how data moves between computers.
2.1 Networks including the Internet
2.1 Networks Including the Internet
Why Create Networks?
A network is two or more computers connected to share resources and communicate.
- Share files and data
- Share hardware (printers)
- Share software (licences)
- Centralised backups
- Communicate (email, messaging)
- Centralised user management
LAN vs WAN
LAN — Local Area Network
- Small geographical area (building/campus)
- Owned and managed by organisation
- High speed (100Mbps–10Gbps)
- Uses: Ethernet cables, Wi-Fi
- Low cost (own infrastructure)
WAN — Wide Area Network
- Large geographical area (city/country/world)
- Uses rented telecoms infrastructure
- Lower speed (varies hugely)
- The Internet is the world's largest WAN
- Higher cost (rented lines)
Network Models
Client-Server Model
- Dedicated server provides services
- Clients request services from server
- Centralised data management
- Server can be single point of failure
- Easier to manage security centrally
- Scales well for large networks
Peer-to-Peer (P2P) Model
- All computers equal (no dedicated server)
- Each peer shares its own resources
- Cheaper — no server hardware needed
- Harder to manage and secure
- Each machine manages own security
- Suits small networks (home)
Thin Client vs Thick Client
| Feature | Thin Client | Thick Client |
|---|---|---|
| Processing | Done on server | Done locally on device |
| Local storage | Minimal or none | Large local storage |
| Hardware cost | Low (simple terminal) | Higher (full computer) |
| Network dependency | Cannot function offline | Can work offline |
| Maintenance | Centralised, easy | Each device separately |
| Example | Chromebook, terminal | Desktop PC, laptop |
Network Topologies
A topology describes how devices are physically or logically connected in a network.
Bus
+ Simple, cheap, easy to extend
– Entire network fails if backbone breaks
Star
+ One device fails → rest work fine
– Central switch = single point of failure
Mesh
+ Highly fault tolerant, multiple paths
– Expensive, complex cabling
Hybrid (Star-Bus)
+ Flexible, scalable
– Complex to manage
Cloud Computing
Definition
Cloud computing provides on-demand access to computing resources (servers, storage, software) over the internet, typically on a pay-per-use basis.
Benefits of Cloud Computing
- Access data from anywhere
- No upfront hardware cost
- Scalable — pay for what you use
- Provider handles maintenance/updates
- Automatic backups
- Disaster recovery built-in
Drawbacks of Cloud Computing
- Requires internet connection
- Data security concerns
- Privacy — data on third-party servers
- Recurring costs can exceed own hardware
- Vendor lock-in
- Limited control over infrastructure
Public vs Private Cloud: A public cloud (AWS, Azure) is shared infrastructure operated by a provider for many customers. A private cloud is owned and operated by a single organisation for their exclusive use.
Transmission Media
| Medium | Speed | Max Distance | Interference | Use Case |
|---|---|---|---|---|
| Copper cable (UTP/STP) | Up to 10Gbps | ~100m | Susceptible to EMI | LAN connections |
| Fibre-optic cable | Up to 100Tbps | Hundreds of km | Immune to EMI | Backbone, ISP links |
| Radio waves (WiFi) | Up to 9.6Gbps (WiFi 6) | ~100m indoors | High (walls, devices) | Wireless LAN |
| Microwaves | Gbps range | Line of sight | Weather-dependent | Point-to-point links |
| Satellites | Mbps–Gbps | Global | High latency | Remote areas, GPS |
LAN Hardware
| Device | Layer | Function |
|---|---|---|
| Switch | Layer 2 | Forwards frames to specific MAC address within LAN |
| Router | Layer 3 | Routes packets between different networks using IP addresses |
| NIC | Layer 1/2 | Network Interface Card — connects device to network; has MAC address |
| WNIC | Layer 1/2 | Wireless NIC for Wi-Fi connections |
| WAP | Layer 1/2 | Wireless Access Point — provides Wi-Fi to devices, connects to wired LAN |
| Bridge | Layer 2 | Connects two network segments, filters traffic by MAC address |
| Repeater | Layer 1 | Amplifies/regenerates signal to extend network range |
Ethernet and CSMA/CD
Ethernet
Ethernet is the standard wired LAN technology. On a shared medium, multiple devices can transmit and cause collisions. CSMA/CD (Carrier Sense Multiple Access / Collision Detection) manages this.
CSMA/CD Process
1. Carrier Sense: Device listens to check if the channel is idle before transmitting.
2. Multiple Access: Multiple devices share the same medium.
3. Transmit: If idle, device transmits the frame.
4. Collision Detection: If two devices transmit simultaneously → collision detected.
5. Jam signal: Both devices send a jam signal to notify all devices.
6. Random backoff: Each device waits a random time before retransmitting.
2. Multiple Access: Multiple devices share the same medium.
3. Transmit: If idle, device transmits the frame.
4. Collision Detection: If two devices transmit simultaneously → collision detected.
5. Jam signal: Both devices send a jam signal to notify all devices.
6. Random backoff: Each device waits a random time before retransmitting.
Bit Streaming
| Type | Description | Example |
|---|---|---|
| Real-time streaming | Data transmitted and played simultaneously (live) | Live sports, video calls |
| On-demand streaming | Pre-stored content buffered then played | Netflix, YouTube |
Bit rate and quality: Higher bit rate = better video quality but requires faster broadband. Low broadband speed relative to bit rate → buffering.
IP Addressing
IPv4
- 32-bit address (4 octets)
- Format: 192.168.1.1
- ~4.3 billion unique addresses
- Address exhaustion is an issue
- Private ranges: 192.168.x.x, 10.x.x.x
IPv6
- 128-bit address (8 groups of 4 hex)
- Format: 2001:0db8:85a3::0001
- 340 undecillion unique addresses
- Solves IPv4 exhaustion problem
- Built-in security features
| IP Address Type | Description |
|---|---|
| Public IP | Globally unique, used on the internet, assigned by ISP |
| Private IP | Used within a LAN, not routable on the internet (e.g. 192.168.x.x) |
| Static IP | Fixed address — same every time. Used for servers. |
| Dynamic IP | Changes each session. Assigned by DHCP. Used for regular clients. |
Subnetting
Subnetting
Subnetting divides a large network into smaller sub-networks using a subnet mask. A device's IP address is split into a network portion and a host portion using the mask. Benefits: improved security, reduced broadcast traffic, better IP management.
URLs and DNS
URL Structure
A URL (Uniform Resource Locator) identifies a resource on the web.
https://www.painlessprogramming.com/chapter1/index.html
Protocol: https · Domain: www.painlessprogramming.com · Path: /chapter1/index.html
DNS Resolution Process (animated)
Internet Support Hardware
| Hardware | Role |
|---|---|
| Modem | Converts digital signals to analogue (for phone lines) and vice versa |
| PSTN | Public Switched Telephone Network — traditional phone infrastructure |
| Dedicated line | Leased line with guaranteed bandwidth, always-on connection |
| Cell phone network | 3G/4G/5G mobile internet access |