Transmission Modes and Bandwidth
Can two devices talk at the same time, or must they take turns?
- Describe simplex, half-duplex and full-duplex modes
- Define bandwidth and throughput
- Match real devices to the correct transmission mode
Overview
Some communication is one-way (a radio station), some is take-turns (a walkie-talkie), and some is both-directions-at-once (a phone call). Choosing the right mode affects the cost and the design of every network. Bandwidth tells us how wide the pipe is; throughput tells us how much actually gets through.
The three modes
Simplex is one-way only — the sender never becomes a receiver. Half-duplex is two-way but only one direction at a time. Full-duplex is two-way at the same instant.
- Simplex: TV broadcast, radio broadcast, temperature sensor to display.
- Half-duplex: Walkie-talkie, CB radio, old Ethernet on a hub.
- Full-duplex: Mobile phone call, modern switched Ethernet, video call.
Bandwidth vs throughput
Bandwidth is the maximum theoretical capacity of a link — measured in bits per second. Throughput is what you actually get after protocol overhead, retransmissions, and congestion. A 100 Mbps school link (bandwidth) often delivers only 40–60 Mbps of useful data (throughput) at peak times. That gap explains why 'the internet is slow' even though the plan number looks big.
Latency and jitter
Two more numbers matter for real-time apps. Latency is the delay from sender to receiver, measured in milliseconds. Jitter is how much that delay varies. Voice and video calls tolerate low bandwidth but hate high latency and jitter — that is why a satellite phone call feels awkward even when the signal is strong.
Classify Six Scenarios
- For each scenario, decide simplex, half-duplex or full-duplex: TV, walkie-talkie, phone call, doorbell, video conference, radio pager.
- Justify each choice in one sentence.
- Which mode allows both parties to talk at once?
Reveal answer
Full-duplex.
- Define bandwidth.
Reveal answer
The maximum data rate a channel can carry, measured in bps.
- Why can a link with high bandwidth still feel slow for a video call?
Reveal answer
High latency or jitter delays and disrupts real-time traffic.
Run a speed test on the school Wi-Fi and note bandwidth, latency (ping) and jitter. Explain which of the three matters most for online lessons.