Data Transmission
IB Syllabus: A2.3.1 – IP addressing, A2.3.2 – Transmission media, A2.3.3 – Packet switching, A2.3.4 – Static and dynamic routing (HL)
Table of Contents
- Key Concepts
- Worked Examples
- Quick Check
- Trace Exercise
- Spot the Error
- Fill in the Blanks
- Predict the Output
- Practice Exercises
- Connections
Key Concepts
IP Addressing (A2.3.1)
IPv4 vs IPv6
IPv4:
- 32-bit address – 4 groups of decimal numbers separated by dots
- Example:
192.168.1.100 - Provides approximately 4.3 billion unique addresses
- Address exhaustion – not enough for all devices worldwide
IPv6:
- 128-bit address – 8 groups of hexadecimal numbers separated by colons
- Example:
2001:0db8:85a3:0000:0000:8a2e:0370:7334 - Provides approximately 340 undecillion (3.4 x 10^38) unique addresses
- Designed to solve IPv4 exhaustion; also improves security and routing efficiency
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Format | Dotted decimal (192.168.1.1) | Hexadecimal colon (2001:db8::1) |
| Total addresses | ~4.3 billion | ~3.4 x 10^38 |
| NAT required? | Often (to conserve addresses) | Not needed (enough addresses) |
| Security | Optional (IPSec add-on) | Built-in (IPSec mandatory) |
Public vs Private IP Addresses
| Type | Scope | Examples | Purpose |
|---|---|---|---|
| Public | Globally unique, visible on the internet | 8.8.8.8 (Google DNS) | Identifies a device/network on the internet |
| Private | Only unique within a local network | 192.168.x.x, 10.x.x.x, 172.16-31.x.x | Used within LANs; not routable on internet |
Multiple devices on a home network share a single public IP address (assigned by the ISP) but each has a unique private IP address (assigned by the router). This is made possible by NAT.
Static vs Dynamic IP Addresses
| Type | Description | Use Case |
|---|---|---|
| Static | Manually configured; does not change | Servers, printers, routers – devices that need a consistent address |
| Dynamic | Automatically assigned by DHCP; may change over time | Laptops, phones, guest devices – temporary connections |
NAT (Network Address Translation)
NAT translates between private and public IP addresses, allowing multiple devices on a LAN to share a single public IP address.
Private Network NAT Router Internet
[PC1: 192.168.1.2] --+
[PC2: 192.168.1.3] --+-- [Router: 192.168.1.1] ---- [Public IP: 203.0.113.5] ---- Internet
[PC3: 192.168.1.4] --+ (NAT table)
How NAT works:
- PC1 sends a request to a web server
- Router replaces PC1’s private IP (192.168.1.2) with the router’s public IP (203.0.113.5)
- Web server responds to 203.0.113.5
- Router checks its NAT table, finds the request came from PC1, and forwards the response to 192.168.1.2
Benefits of NAT:
- Conserves public IP addresses – one public IP serves many private devices
- Security – private IP addresses are hidden from the internet; external attackers cannot directly target internal devices
- Flexibility – internal network can be reorganised without changing the public IP
Transmission Media (A2.3.2)
Fibre Optic Cable
- Transmits data as light pulses through thin glass/plastic strands
- Very high bandwidth, long range, immune to electromagnetic interference
- Expensive to install, fragile, requires specialist equipment for repair
Twisted Pair Cable (e.g., Ethernet/Cat5e/Cat6)
- Copper wires twisted together to reduce interference
- Most common wired connection in LANs
- Lower cost, easy to install, but shorter range and lower bandwidth than fibre
- Susceptible to electromagnetic interference (EMI)
Wireless (Wi-Fi, Radio)
- Transmits data as radio waves
- No physical cables needed – flexible, mobile
- Susceptible to interference (walls, other devices), limited range, security concerns (signals can be intercepted)
Comparison of Transmission Media
| Factor | Fibre Optic | Twisted Pair | Wireless |
|---|---|---|---|
| Bandwidth | Very high (up to 100 Gbps) | Moderate (up to 10 Gbps for Cat6a) | Moderate (varies by standard) |
| Installation | Complex, specialist equipment | Simple, standard tools | Simplest (no cables) |
| Cost | High | Low | Moderate (APs needed) |
| Range | Very long (km) | Short (up to 100m) | Limited (30-100m indoors) |
| Interference | Immune to EMI | Susceptible to EMI | Susceptible (walls, devices) |
| Attenuation | Very low | Moderate | High (varies with obstacles) |
| Reliability | Very high | High | Moderate (signal drops) |
| Security | Very secure (hard to tap) | Secure (physical access needed) | Less secure (signals broadcast) |
Exam tip: When comparing transmission media, always link back to the specific factors: bandwidth, complexity of installation, cost, range, susceptibility to interference, attenuation, reliability, security. These are the IB-specified factors.
Packet Switching (A2.3.3)
When data is sent across a network, it is not sent as one continuous stream. Instead, it is broken into packets.
Packet Structure
+------------------+------------------+------------------+
| HEADER | PAYLOAD | TRAILER |
+------------------+------------------+------------------+
| Source IP | The actual data | Error checking |
| Destination IP | (a portion of | (checksum) |
| Protocol | the original | |
| Packet number | file/message) | |
| Total packets | | |
+------------------+------------------+------------------+
Header contains routing and reassembly information (source/destination IP, packet number, protocol). Payload contains the actual data. Trailer contains error-checking information (checksum) to verify data integrity.
How Packet Switching Works
- Segmentation – the sending device breaks the data into small packets
- Header attachment – each packet gets a header with source IP, destination IP, packet number, and total packet count
- Independent routing – each packet is sent independently and may take different routes through the network
- Routing decisions – routers examine each packet’s destination IP and forward it along the best available path
- Reassembly – the receiving device uses packet numbers to reassemble the packets in the correct order
- Error checking – the trailer’s checksum is verified; corrupted packets are requested again (if using TCP)
Sender Receiver
| |
|--[Pkt 1]--> Router A --> Router C ----------> [Pkt 1]--|
|--[Pkt 2]--> Router A --> Router B --> Router D -> [Pkt 2]--|
|--[Pkt 3]--> Router B --> Router D ----------> [Pkt 3]--|
| |
Packets take different routes Reassembled in order at destination
Role of Switches and Routers in Packet Switching
| Device | Role in Packet Switching |
|---|---|
| Switch | Forwards packets within the same LAN using MAC addresses; examines the destination MAC in the frame header |
| Router | Forwards packets between different networks using IP addresses; examines the destination IP in the packet header and determines the best path |
A common exam mistake is saying “the router sends all packets along the same path.” In packet switching, each packet is routed independently – different packets in the same message may take different routes through the network. This is a key advantage: if one route is congested or fails, packets can take alternative paths.
Enrichment: Packet Switching Step-by-Step
This goes beyond the IB syllabus but helps build understanding.
Throughput vs Goodput:
- Throughput = total data transmitted per second (including headers, retransmissions, and protocol overhead)
- Goodput = useful data received per second (excluding overhead)
- Goodput is always less than throughput because every packet carries headers and trailers in addition to the actual data
Static and Dynamic Routing (A2.3.4)
HL Only – Static and dynamic routing are assessed at HL only.
Static Routing
- Routes are manually configured by a network administrator
- The routing table is fixed – it does not change unless manually updated
| Advantages | Disadvantages |
|---|---|
| Simple to configure on small networks | Does not adapt to network changes (link failures) |
| Predictable – data always takes the same path | High maintenance – must manually update every change |
| Secure – no routing protocol traffic to intercept | Does not scale well for large networks |
| Low resource usage (no routing algorithm running) | No load balancing – cannot spread traffic across paths |
Dynamic Routing
- Routers automatically discover and update routes using routing protocols
- Routing tables update in response to network changes (e.g., link failures, congestion)
| Advantages | Disadvantages |
|---|---|
| Adapts to network changes automatically | More complex to set up and troubleshoot |
| Scales well for large networks | Higher resource usage (CPU, memory for routing algorithms) |
| Load balancing – can distribute traffic across paths | Routing protocol traffic consumes bandwidth |
| Fault tolerance – reroutes if a link fails | Convergence time (delay before all routers agree on new routes) |
Comparison of Static and Dynamic Routing
| Factor | Static Routing | Dynamic Routing |
|---|---|---|
| Configuration | Manual | Automatic |
| Maintenance | High (manual updates) | Low (self-updating) |
| Complexity | Simple | Complex |
| Resource usage | Low | Higher (routing algorithms) |
| Convergence | Instant (no change needed) | Takes time after a change |
| Scalability | Poor (small networks) | Good (large networks) |
| Network size | Small LANs | Large LANs and WANs |
When to use which? Static routing is appropriate for small, stable networks (e.g., a home office with one internet connection). Dynamic routing is appropriate for large, complex networks where links may fail or traffic patterns change (e.g., a corporate WAN with multiple paths between sites).
Worked Examples
Example 1: IP Address Classification
Classify each IP address and explain its purpose.
| # | IP Address | Type | Explanation |
|---|---|---|---|
| 1 | 192.168.0.1 | Private, IPv4 | 192.168.x.x is a private range; typically a home router’s default address |
| 2 | 8.8.8.8 | Public, IPv4 | Globally unique; this is Google’s public DNS server |
| 3 | 10.0.0.50 | Private, IPv4 | 10.x.x.x is a private range; used within an organisation’s LAN |
| 4 | 2001:0db8::1 | IPv6 | 128-bit hexadecimal format; part of the IPv6 addressing scheme |
| 5 | 172.16.5.10 | Private, IPv4 | 172.16-31.x.x is a private range |
Example 2: Packet Journey
Trace a packet from a student’s laptop to a web server:
| Step | What Happens | Device Involved |
|---|---|---|
| 1 | Data is broken into packets; headers added with source/dest IP | Student’s laptop |
| 2 | Packet sent to the local network switch | NIC –> Switch |
| 3 | Switch forwards to the router (different network) | Switch –> Router |
| 4 | Router uses NAT to replace private IP with public IP | Router (NAT) |
| 5 | Packet is forwarded across the internet (multiple routers) | Internet routers |
| 6 | Packet arrives at the web server’s network router | Destination router |
| 7 | Router forwards to the switch, then to the web server | Switch –> Web server |
| 8 | Web server reassembles all packets using packet numbers | Web server |
Quick Check
Q1. How many unique addresses can IPv4 provide?
Q2. What is the primary function of NAT?
Q3. Which transmission medium is immune to electromagnetic interference?
Q4. In packet switching, what information does the packet header contain?
Q5. (HL) Which type of routing adapts automatically when a network link fails?
Trace Exercise
Trace a packet’s journey from Computer A (private IP: 192.168.1.5) through a NAT router (public IP: 203.0.113.10) to a web server (93.184.216.34). Fill in the source and destination IP addresses at each stage.
Trace: NAT Address Translation
Computer A (192.168.1.5) sends a request to a web server (93.184.216.34) through a NAT router (public IP: 203.0.113.10). The web server then sends a response back.
| Step | Location | Source IP in Packet | Destination IP in Packet |
|---|---|---|---|
| 1 | Computer A sends packet | ||
| 2 | After NAT translation | ||
| 3 | Web server sends response | ||
| 4 | After NAT reverse translation |
Spot the Error
A student wrote revision notes about packet switching. One line contains an error. Click the line with the error, then pick the correct fix.
Pick the correct fix for line 2:
Fill in the Blanks
Complete the summary of data transmission by filling in the correct term for each blank.
Fill in the blanks to complete this summary of data transmission:
DATA TRANSMISSION
=================
translates between private and public IP addresses.
uses 128-bit addresses to solve the address exhaustion problem of IPv4.
In packet switching, data is broken into with headers containing routing information.
cables transmit data as light pulses and are immune to electromagnetic interference.
A IP address is automatically assigned by DHCP and may change over time.
Predict the Output
A home network has 4 devices connected to a router. The ISP assigns the router one public IP address: 203.0.113.5. How many public IP addresses are used in total?
Type a number:
A packet is sent from IP address 10.0.0.5 to 8.8.8.8. Is the source address public or private?
Type Public or Private:
Practice Exercises
Core
-
IP Addressing – Explain the difference between IPv4 and IPv6. Why was IPv6 developed?
-
Transmission Media – Create a table comparing fibre optic, twisted pair, and wireless transmission across four factors: bandwidth, cost, range, and interference susceptibility.
-
Packet Switching – Describe the process of packet switching, including the role of the packet header, payload, and trailer. Explain why packets might take different routes.
Extension
-
NAT Explained – A small business has 50 computers but only 1 public IP address from their ISP. Explain how NAT allows all 50 computers to access the internet simultaneously. Include a diagram in your answer.
-
Media Selection – A new school is being built. Recommend the most appropriate transmission medium for: (a) connecting the server room to each classroom, (b) providing internet access in the library, (c) connecting the school to the ISP 2 km away. Justify each choice.
Challenge
- Routing Comparison (HL) – A company has 5 offices connected by a WAN. Compare static and dynamic routing for this network. In your answer, discuss: (a) which approach is more appropriate and why, (b) what happens when a link between two offices fails under each approach, (c) the trade-offs in resource usage, complexity, and scalability, and (d) the concept of convergence and why it matters.
Connections
- Prerequisites: Network Fundamentals – understanding network types (LAN, WAN) and devices (routers, switches) that handle data transmission
- Prerequisites: Protocols and Layers – TCP/IP protocols define how packets are formatted and delivered
- Related: Number Systems – IP addresses are fundamentally binary numbers; IPv4 is 32 bits, IPv6 is 128 bits
- Forward: Network Security – NAT provides a layer of security; packet inspection is used by firewalls
- Forward: Encryption – data in packets can be encrypted to prevent interception during transmission