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Medium Access Control
Channel access methods and collision resolution protocols
Key Concepts
ALOHA, CSMA/CD, token passing, collision detection
Applications
Ethernet, Wi-Fi, satellite networks, token ring LANs
Exam Focus
Throughput calculations, protocol comparison, efficiency analysis
MAC Protocol Topics
ALOHA Protocols Details
ALOHA Throughput Calculator
G = 0.5
Pure ALOHA
Formula: S = G × e^(-2G)
Throughput (S): 0.1839
Maximum S: 0.184 at G = 0.5
Slotted ALOHA
Formula: S = G × e^(-G)
Throughput (S): 0.3033
Maximum S: 0.368 at G = 1
Throughput Comparison
Throughput vs Offered Load Graph
Current Performance:
Pure ALOHA:18.4%
Slotted ALOHA:30.3%
Improvement:64.9%
ALOHA Protocol Comparison
| Aspect | Pure ALOHA | Slotted ALOHA |
|---|---|---|
| Transmission | Anytime | Only at slot boundaries |
| Vulnerable Period | 2 × Frame time | 1 × Frame time |
| Maximum Throughput | 18.4% | 36.8% |
| Synchronization | Not required | Required |
| Complexity | Simple | Moderate |
| Applications | Early satellite networks | RFID, some wireless systems |
📝 Exam Preparation Tips
Key Topics to Master
- • Calculate ALOHA throughput for different offered loads
- • Understand CSMA/CD binary exponential backoff
- • Know token ring frame format and priority mechanism
- • Compare efficiency of different MAC protocols
- • Analyze collision domains and broadcast domains
Common Exam Questions
- • "Calculate maximum throughput of Slotted ALOHA" (4 marks)
- • "Explain CSMA/CD operation with timing diagram" (6 marks)
- • "Compare token ring vs Ethernet protocols" (8 marks)
- • "Analyze binary exponential backoff algorithm" (5 marks)
- • "Draw and explain token ring frame format" (4 marks)