https://www.mattkeeter.com/blog/2022-08-11-udp/
UDP is a transport-level protocol for sending messages through an IP network.
It sits at level 4 in the OSI model:
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data link
1 PhysicalLike many of you, I've got hardware on my desk that's sending UDP packets, and the time has come to take a closer look at them.
Most "low-level" networking tutorials will bottom out somewhere at "use tcpdump to see raw packets". We'll be starting a bit lower in the stack; specifically, here:
[Picture of Probes soldered to a circuit board]
This is a high-speed active differential probe soldered to an Oxide Computer Company rack switch. We're going all the way down to the metal.
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From Oscilloscope to Wireshark: A UDP Story
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(Score: 5, Informative) by soylentnewsfan1 on Sunday August 14 2022, @06:03AM (1 child)
The author posted this story to HackerNews where there are a couple more comments by them and an interesting anecdote of a similar level for those that are interested in such things.
https://news.ycombinator.com/item?id=32428032 [ycombinator.com]
(Score: 2) by janrinok on Sunday August 14 2022, @06:27AM
[nostyle RIP 06 May 2025]
(Score: 0) by Anonymous Coward on Sunday August 14 2022, @06:09AM (1 child)
As someone who used to work with packets, I didn't really feel like TFA was in familiar territory until I read "ethernet frame preamble!", and because you used that exclamation mark I bet you felt good to be back up in octet world and away from oscilloscopes. I never had to go there for any reason.
(Score: 4, Funny) by driverless on Sunday August 14 2022, @07:30AM
Whatever you do, don't say that name out loud. Friend of mine did it a while back and that was the last we heard of him. Apparently a sandgorgon turned up shortly after he said the name.
(Score: 3, Interesting) by Anonymous Coward on Sunday August 14 2022, @07:29AM
Notable for IP layer in general:
* IP packet fragmentation [wikipedia.org]
* Out of order delivery [wikipedia.org]
Can be used in combination to make deep packet inspection so much harder (or the connection kicked out if the routers can't handle the abuse).
Low bandwidth and depends on the reliability of the network, but one can tunnel TCP (and higher order protocols) over ICMP [mit.edu] (homework: write your own HTTPING server).
(Score: 5, Interesting) by Rupert Pupnick on Sunday August 14 2022, @01:48PM
Good article, but I think it creates a bit of confusion about timing at the scope versus timing at the actual receiver.
The scope capture is well done, but you can see from the display that it's a single shot self triggered capture of the waveform. There's no periodic clock signal into the scope.
The real timing issue is at the receiver which has to recover the clock to latch the data values from that very same data signal. This is one of the main purposes of 8B10B coding: it guarantees a mininum transition density (or equivalently a maximum run length of the same bit value) needed for the clock recovery circuit at the receiver.