Ethernet, CSMA/CD, LAN hardware and IP addresses
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Taking turns to talk
- Ethernet
- How CSMA/CD works
Read the transcript of the teaching part
Last time
Before we start: last time, in Client-server, cloud, Ethernet, streaming and IP addresses, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Taking turns to talk
A room of people all talking at once is noise. Ethernet networks solve this by listening first, and talking only when nobody else is. If two people start together, both stop and try again after a random pause. Each device also needs an address, so messages reach the right place, and that is what IP addresses and subnets give you.
Ethernet
Ethernet is the standard for wired local area networks. Devices send data in frames, each with the sender's and the receiver's hardware address. On a bus, all devices share one cable. If two devices send at the same moment, their signals collide and the data is corrupted. CSMA/CD, carrier sense multiple access with collision detection, is the method used to manage that.
How CSMA/CD works
Carrier sense: a device listens to see if the cable is idle before it sends. Multiple access: many devices share the cable. If the cable is idle, it sends and keeps monitoring. If it detects a collision, it stops and sends a jam signal so that every device knows. Each device waits a random time before trying again. The random wait stops the same two devices from colliding repeatedly.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Hardware devices.
The whole chapter: Hardware.
Chapter 2: Communication
- Bit streaming, client-server, peer-to-peer and cloud computing 6 min
- Ethernet, CSMA/CD, LAN hardware and IP addresses 7 min
- LAN, WAN, topologies and wired and wireless networks 7 min
Also for A Level Computer Science 9618
Which topics come up most in A Level Computer Science 9618 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.