# Q1(b) · Ideal broadcast channel and slotted ALOHA

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2023-jan-ai-reexam/q1b

Canonical: https://deep-learning-study-room.vercel.app/read/cn/tee/papers/paper-2023-jan-ai-reexam--q1b/

Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.

### Q1(b). State four desirable characteristics of a broadcast channel. Which does slotted ALOHA have, and why? [5 marks]

### Answer

| Ideal characteristic | Slotted ALOHA |
| --- | --- |
| One active node uses rate R | Yes, at slot boundaries with no collisions; an initial wait may occur |
| M active nodes each achieve R/M | Not in general: collisions and empty slots waste capacity |
| Decentralized without master or clock synchronization | No master is needed, but all nodes must synchronize slots |
| Simple | Yes: transmit at a slot boundary, then retry after random backoff |

The standard independent-attempt throughput maximum approaches1/e≈0.368 of the channel as the contender count becomes large, so it does not deliver ideal full utilization under contention.