Analyzing actual Ethernet encoding | Networking tutorial (4 of 13)
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange users link it when explaining or asking how Ethernet signals look on the wire, including line coding, voltage levels and how to probe a link with a scope.
Recommended by 1 people across 1 different months, 2021 to 2023.
What it is
Ben Eater connects an oscilloscope to a live 10 Mbit Ethernet link and reads the signal on the wire. He decodes the Manchester-encoded differential voltage by hand to recover the bytes of an actual message. It is part 4 of his 13-part networking tutorial series.
What people said
Recommends M.X · 2021-08 · Electrical Engineering Stack Exchange · on “How can a Cat 5 cable (frequency 100 MHz) transmit 2.5 gigabits/second?”
Thanks to @Justme and @MarcusMüller for pointing me in the right direction. I found this video [this video] by Ben Eater which answers my question quite well. Basically, the frequency of 100 MHz is not directly related to the bits pre second that get transmitted. I assumed there was one signal (a square wave or something) per pair, which is not the case. Instead, sine wave modulation is used to transmit "symbols", which can be just ones and zeros (that's the case for slow transmissions like 10BaseT), but for gigabit ethernet, a symbol can have more than two states. This is part of the Line Code that @Nstorm mentioned. See this table [LINK] for which ethernet variant uses which line code. The symb
Cites Mac_79 · 2021-04 · Electrical Engineering Stack Exchange · on “How do you input the voltage signal to an oscilloscope?”
I was watching this tutorial on "analyzing actual Ethernet encoding" [this video] [LINK] Orange pair is transmitting data to the oscilloscope and the green pair is receiving data to the right. This oscilloscope measures the voltage across the two wires of the orange pair and plots that voltage over time on the graph. [LINK] Using Manchester coding, he's decoded 16 bits. The first byte is 75 (K), the second is 65 (A). My question is, how did he input "K" and "A" in the first place, which then shows up on the oscilloscope? Is it as simple as typing "K" and "A" on the keyboard? I want to know this so that I can replicate this experiment by myself should I wish to. Thanks!
Cites s3b4s · 2021-04 · Electrical Engineering Stack Exchange · on “How is data transferred through wires? is it [5,0] volts (DC) or is it [1,-1] volts (AC)?”
So basically I am learning about how data is transferred through wires for a networking course and I stumbled upon this [this video] Ben Eaters video on this topic and I got a bit confused because I know that computers use 5 volts (DC) to communicate with for example a USB device and I also know that mains power is 110 or 220 volts (AC) at 50 or 60 Hz but when Ben explains how in his oscilloscope data is been transferred by detecting transition states in fluctuations of 1 to -1 volts I interpreted this as the 1v (DC) been turned into Alternating Current in order to send data. Is Alternating Current how every data communication is carried? How is it in USB? Can someone clarify what I'm saying here
Cites xenia · 2021-08 · Electrical Engineering Stack Exchange · on “What voltage difference should I use for 10BASE-T?”
Looking through some resources about the electronics behind ethernet, specifically the 10BASE-T standard, I've found some conflicting information about what the voltage differential should be for the signals sent. The Wikipedia page for Ethernet over twisted wire [LINK] states that A 10BASE-T transmitter sends two differential voltages, +2.5 V or −2.5 V. This claim does cite a source, however I cannot access it. In contrast, the the 802.3-1985 IEEE-standard states: [the maximum voltage difference], shall be < 1315mV [W]hen the A lead is 160mV positive with respect to the B lead, the interface circuit is in the HI state, and when the A lead is 160mV negative with respect to the B lead, the in
Cites ori6151 · 2023-01 · Electrical Engineering Stack Exchange · on “Is it possible to measure 10/100baseT with a regular oscilloscope probe?”
I want to measure the waveforms of ethernet signals (both RX and TX at the same time) using the DSO-X 1024G [LINK] oscilloscope (200 MHz, 1 GS/s, 4 channels). My plan is to connect 2 oscilloscope probes across 2 pairs (TX/RX). Like this (but 2 pairs not 1): [LINK] From Ben Eater - Analyzing actual Ethernet encoding | Networking tutorial (4 of 13) [this video] Do I need differential probes to measure more than 1 signal at a time? (Since I want to measure both RX and TX) BTW - I know there are better ways to measure Ethernet signals. I want to use an oscilloscope to learn about ethernet encodings and decode the line coding myself manually.