Talk:3295: Semaphore

It's not directly to the speed of light that the speed of moving flags should be compared (in terms of signal transmission, as Randall rightly points, semaphore is faster), it is rather the rate at which a new semaphore symbol can be dialled (typically one of the half-a-dozen to a dozen patterns a given semaphore can present). If calculating the information flow, that dialling rate (thus speed of moving the flags divided by a typical size of semaphore, ie about 10 per second if moving a 10 cm semaphore at 1 m/s) times the number of possible patterns (let's say 8) should be compared to the baud rate (typically $10^11$ per second) times 2 to the power of the number of lanes (let's say 3). For the data chosen, we're comparing approximately 80 bits per second for semaphore to $8\cdot10^11$ for the optical fibre. This is the rate at which a permanent flow of information can be transmitted (if we consider that deciphering the semaphore pattern is faster than dialling it, so in the situation where the operator or software getting the image from the webcam is at least as fast as the dialling). However, this doesn't tell us about the latency time: how much time does it take for an elementary 8-bit signal to reach destination. That time is obtained by summing the time of "dialling" (or modulating the numerical signal for the optic fibre), plus the time it travels in air or fibre (faster in the former, that's where semaphore can try to catch up!), plus the deciphering/demodulating at reception. --2001:1C04:2F0B:5300:3C9D:4D7A:7E6C:66E7 20:37, 7 September 2026 (UTC)

I think I addressed what you just said there, before spotting that you'd been making this point. There's elements of latency, lag, bandwidth and so on in the basic transmission rate. I think I managed to make a brief but salient edit to sort of cover that, but YMMV. 92.23.7.14 23:14, 7 September 2026 (UTC)

Basically, Opto-isolators writ large. --79.16.224.49 22:15, 7 September 2026 (UTC)

Propagation speed through whatever medium (air, fiber optic glass, copper, etc.) doesn't practically contribute to latency over short distances. Local latencies are dominated by processing at either end (or dropped packets). 75.230.130.169

What are sensitive components, in this context? Student Driver (talk) 01:33, 8 September 2026 (UTC)

Electrically sensitive I would assume. If there is a power problem in on system (say some type of ground fault or a lighting strike) larger than design current can flow in the network wiring. There is a rule you never run copper between two buildings for this reason. Lordpishky (talk) 03:39, 8 September 2026 (UTC)

The explanation should probably explain what air gaps are in networking. An architect (talk) 01:45, 8 September 2026 (UTC)

Only if it explains that this example is not an actual networking air gap, though. 92.23.7.14 12:47, 8 September 2026 (UTC)

I think the comic is talking about a physical air gap, which is used to isolate electrical components. The use of this term for secure networking is metaphorical, similar to firewall. Barmar (talk) 17:23, 8 September 2026 (UTC)

Randall is offering a ludicrous suggestion but the current explanation fails to a) discuss why it is useful to separate sensitive components and b) why this suggestion is impracticable. Inquirer (talk) 02:04, 8 September 2026 (UTC)

I guess I'm just waiting for the relevant implementation on GitHub to link in the explanation now. GreyFox (talk) 02:28, 8 September 2026 (UTC)

While not as widely implemented as IP over Avian Carriers, there still is an "official" way to send IP diagrams using the Semaphore Flag Signaling System. See RFC 4824. 2A01:36D:1300:2A53:132B:E6E3:5CB5:54C9 04:35, 8 September 2026 (UTC)

I have tried to calculate the speed at which the flag arms need to move in order for this setup to save any time. My first edit on the wiki - hope I did it right. --KeizerHarm (talk) 16:11, 8 September 2026 (UTC)

The explanation should probably explain what "semaphores" usually refer to in computing as I believe that's an intended allusion/pun here; controlling access to common resources which could be construed to be "sensitive". 136.226.154.84 16:41, 8 September 2026 (UTC)

Is it worth mentioning that some electronic connections, especially MIDI, use optical isolation with a LED and light sensitive resistor to prevent problems with earth loops and voltage differences. 80.41.5.152 16:52, 8 September 2026 (UTC)

I added a paragraph about laser links. At my university we had/have such a system. When it worked it was great (I am not sure but I think it was 100Mb/s across 2kms). The main problem was that slightly movements of the buildings (probably due to thermal expansion/contraction) were enough to lose the signal (I just checked and an error of only 1 degree gives a ~35 meters error at the other side). Also, in case of fog or rain it also lost signal. Not sure what was the wavelength, probably red or near-infrared. Rps (talk) 18:05, 8 September 2026 (UTC)

Should we also address the framerate of the camera? Most consumer-grade cameras have an fps in the low three-digit range (or even less), which limits the bitrate dramatically. --Coconut Galaxy (talk) 07:26, 9 September 2026 (UTC)

The comic appears to be referencing the use of semafores in software in the context of physical semafore. Software semafore gaps or race conditions occur in multi thread software with poor semafore control. All this discussion on light speed is missing the joke completely. Randle is implementing a physical protection against a software issue. -- [[User:|]] ([[User talk:|talk]]) Panda (19:41, 11 September 2026)

I had pondered adding some more on Semaphore (programming), myself, but it really doesn't look like there are any actual analogies towards that embedded in the comic, which is so much more tied to being an OSI Level 1 situation. 78.151.45.228 20:29, 11 September 2026 (UTC)

DO NOT CLICK ON REFRESH IT IS A PHISHING LINK!!! 14231423 (talk) 03:09, 13 September 2026 (UTC)

Not necessarily, but the problem has been noted and should be being noticed/dealt with. If it isn't, then perhaps better letting them know on the Community Portal discussion topic, as it's more likely to be sorted (and/or made into a more global warning) and yet it should only occasionally be an actually correct warning for other people who read your duplicate warning. 78.151.45.228 17:29, 13 September 2026 (UTC)

This is actually a thing. I've seen a write-up of Semaphore Transmission Protocol somewhere. 31.185.224.8 21:58, 14 September 2026 (UTC)

As per mentioned in the #Trivia? 78.151.45.228 23:05, 14 September 2026 (UTC)