4.0 Wireless Networking
Wireless Networking Challenges
Core Challenge Categories
| Challenge Type | Specific Issues | Impact on Network Design |
|---|
| Physical Signal Issues | Attenuation (rain, water, dust) | Higher error rates, need for error correction |
| Reflections (water bodies, fog) | Signal distortion, multipath effects |
| Diffractions (hills, buildings) | Coverage gaps, dead zones |
| Infrastructure Constraints | Antenna icing | Service interruption, maintenance requirements |
| Zoning restrictions | Limited transmission power, reduced coverage |
| Device Limitations | Power consumption (especially IoT) | Battery life considerations, sleep modes |
| Security Vulnerabilities | Wide signal propagation | Open to eavesdropping, need for encryption |
Error Rate Comparison
Wired Networks: [Low Error Rate] ████░░░░░░ (10-30%)
Wireless Networks: [Higher Error Rate] ███████░░░ (70-90%)
IEEE 802.11 (WLAN) Architecture
WLAN Design Goals and Trade-offs
| Goal | Benefit | Trade-off/Challenge |
|---|
| Ease of use | Simple setup and roaming | Potential security vulnerabilities |
| Power efficiency | Extended battery life | May limit transmission power/range |
| License-free operation | No regulatory costs | Interference from other devices |
| Robustness to noise | Reliable communication | Complex error correction needed |
| Global usability | Universal deployment | Different regional regulations |
| Security | Protected communications | Performance overhead |
Security Protocol Evolution
WEP (Weak) → WPA → WPA2 → WPA3 (Current)
↓ ↓ ↓ ↓
Broken Better Strong Strongest
Note: All protocols only protect wireless links, not end-to-end communication.
WLAN Network Types Comparison
| Aspect | Ad Hoc (IBSS) | Infrastructure |
|---|
| Central Control | None | Access Point (AP) |
| Connectivity | Direct peer-to-peer | All through AP |
| Range Limitation | Nodes must be in direct range | Extended through AP relay |
| Wired Network Access | No | Yes (via AP) |
| Typical Duration | Short-lived | Permanent/Long-term |
| Scalability | Limited (small groups) | High (multiple APs) |
| Relay Capability | No | Yes (AP provides buffering) |
IEEE 802.11 Architecture Hierarchy
Extended Service Set (ESS)
├── Basic Service Set 1 (BSS1)
│ ├── Access Point 1
│ ├── Station A
│ ├── Station B
│ └── Station C
├── Basic Service Set 2 (BSS2)
│ ├── Access Point 2
│ ├── Station D
│ └── Station E
└── Distribution System (DS)
└── Connects all APs
Example: University campus network (Unifi) = ESS with multiple BSSs
Service Classification
| Service Category | Specific Services | Primary Function |
|---|
| Station Services | Authentication | Verify device identity |
| De-authentication | Remove authenticated station |
| Privacy | Prevent eavesdropping |
| Data delivery | Transport data packets |
| Distribution Services | Association | Link station to AP |
| Mobility management | Handle roaming between APs |
| Integration | Connect to other network types |
Medium Access Control (MAC) - Key Differences
| Protocol | Detection Method | Timing | Use Case |
|---|
| Ethernet CSMA/CD | Collision Detection | AFTER collision occurs | Wired networks |
| Wireless CSMA/CA | Collision Avoidance | BEFORE transmission | Wireless networks |
RTS/CTS Mechanism Visualization
Scenario: Station A wants to send data to Station B
Step 1: Station A broadcasts RTS
A ----[RTS]----> B
\ /
\ /
v v
C D
(hears RTS, (hears RTS,
defers) defers)
Step 2: Station B responds with CTS
A <---[CTS]----- B
^ ^
\ /
\ /
C D
(hears CTS, (hears CTS,
defers) defers)
Step 3: Data transmission
A =====[DATA]===> B
(Other stations remain silent)
Binary Exponential Backoff Calculation Example
Problem: Station fails to receive CTS after sending RTS. Calculate backoff time.
| Attempt | Backoff Window | Random Slots | Wait Time (if slot = 20μs) |
|---|
| 1st | 0 to 2^1-1 = [0, 1] | Random(0, 1) | 0μs or 20μs |
| 2nd | 0 to 2^2-1 = [0, 3] | Random(0, 3) | 0μs, 20μs, 40μs, or 60μs |
| 3rd | 0 to 2^3-1 = [0, 7] | Random(0, 7) | 0μs to 140μs |
| nth | 0 to 2^n-1 | Random(0, 2^n-1) | Exponentially increasing |
Full Duplex Analysis
| Configuration | Simultaneous TX/RX | Collision Risk | Implementation |
|---|
| Single Channel | Impossible | High | Standard CSMA/CA |
| Multiple Channels | Possible | Low | Separate TX/RX channels |
| Advanced Techniques | Limited | Medium | Interference cancellation |
| Standard | Max Bandwidth | Frequency | Real-world Performance |
|---|
| 802.11b | 11 Mbps | 2.4 GHz | ~5-6 Mbps |
| 802.11g | 54 Mbps | 2.4 GHz | ~25-30 Mbps |
| 802.11n | 100+ Mbps | 2.4/5 GHz | ~50-70 Mbps |
Performance Degradation Factors: * Interference and fading * Distance from AP * Number of concurrent users * Environmental obstacles
Bluetooth / Personal Area Network (PAN)
Bluetooth vs IEEE 802.11 Comparison
| Feature | Bluetooth | IEEE 802.11 (WiFi) |
|---|
| Range | ~10 meters | 100+ meters |
| Frequency | 2.45 GHz ISM | 2.4 GHz, 5 GHz ISM |
| Primary Use | Device connectivity | Internet access |
| Power Consumption | Low (especially BLE) | Higher |
| Network Topology | Piconet/Scatternet | BSS/ESS |
| Max Devices | 7 active slaves per master | Hundreds per AP |
| Application Focus | Cable replacement | Data networking |
| Protocol Layers | Physical, Link, MAC | MAC, Physical |
Bluetooth Network Topology
Piconet 1 Piconet 2
M1 M2
/|\ /|\
/ | \ / | \
S1 S2 S3 S4 S5 S6
| |
+-------- Bridge -----------+
(Scatternet)
M = Master device
S = Slave device
Key Constraints: * Each piconet: 1 master + up to 7 active slaves * Scatternet: Multiple interconnected piconets * Bridge device can be slave in multiple piconets
Bluetooth Applications and Use Cases
| Application Category | Examples | Power Requirements |
|---|
| Data/Voice Access | Headsets, speakers | Standard Bluetooth |
| Cable Replacement | Keyboards, mice, printers | Standard Bluetooth |
| IoT Sensors | Health monitors, beacons | Bluetooth Low Energy (BLE) |
| File Transfer | Phone to laptop | Standard Bluetooth |
Power Consumption Analysis
Standard Bluetooth: ████████░░ (High power)
Bluetooth LE (BLE): ██░░░░░░░░ (Very low power)
Battery Life Impact:
IoT Device with Standard BT: Days to weeks
IoT Device with BLE: Months to years
Wireless Technologies Summary
Frequency Band Utilization
| Technology | Frequency | Band Type | License Required |
|---|
| IEEE 802.11b/g/n | 2.4 GHz | ISM | No |
| IEEE 802.11a/n/ac | 5 GHz | ISM | No |
| Bluetooth | 2.45 GHz | ISM | No |
ISM Band Advantages: License-free operation, global availability ISM Band Disadvantages: Interference from other devices (microwaves, etc.)
Technology Selection Matrix
| Use Case | Range Needed | Device Count | Power Sensitivity | Recommended Technology |
|---|
| Home Internet | High | Many | Low | IEEE 802.11 |
| Device Pairing | Low | Few | Medium | Bluetooth |
| IoT Sensors | Low | Many | High | Bluetooth LE |
| Enterprise Network | High | Very Many | Low | IEEE 802.11 with multiple APs |
Common Exam Calculation Types
1. Backoff Time Calculation Given: Collision attempt number n, slot time Formula: Backoff window = [0, 2^n - 1] Wait time = Random_slot × Slot_time
2. Throughput Estimation Factors: Nominal bandwidth, interference level, distance, concurrent users Real throughput ≈ Nominal × Efficiency_factor
3. Range vs Power Trade-off Higher transmission power = Greater range but higher power consumption Lower power (BLE) = Shorter range but extended battery life