[Starlink] 300ms Telecommunication Latency and FTL Communication

[David Lang]

On Fri, 7 Jun 2024, Colin_Higbie wrote:

> GREAT, GREAT point on the increased likelihood of unintentional interruptions 
> and talking over each other the higher the latency. I had not thought of that 
> before, but I think that's a compelling and easily measurable metric. It also 
> gives a clear cost-based selling advantage to the ISP with lower latency, 
> which should make it attractive to business: if an ISP can say to a business 
> (or at-home worker): based on our 20ms lower latency, you will save 3 minutes 
> per day in lost annoyances due to accidental interruptions, that has a value 
> per person in those calls of $X. Therefore, you should switch your business to 
> us.
>
> I do still think, at least for me as a speaker, that video feedback that does 
> not "feel" like it provides instant video feedback in the form of real-time 
> facial expressions to show audience feedback for the speaker is more critical 
> (I can stomach small delays on audio feedback after I ask a question, but not 
> on video feedback, which I need while I'm talking), but I do think the 
> interruption piece is also very real. Further, my point on video is almost 
> binary – either I'm getting close enough to real-time feedback or I'm not and 
> need to plod on without it, which diminishes its value as an argument for 
> lower latency.

the problem is drawing the line at what latency is the problem. This is going to 
be different for different people and take quite a bit of experimentation to 
discover (and I would not be surprised if someone who is doing testing is 
learing how to cope with longer latencies, so you can't just increase/decrease 
the latency in a predictable manner, you would need to randomize it and ask 
after each call how good/bad it was)

> In contrast, the increase in accidental interruptions in audio (and video too 
> presumably) would scale with latency (not binary means much better for an 
> argument to the ISP). Every 1ms of additional latency would provide a small 
> but measurable % increase in the amount of accidental interruptions. 
> Conversely, the lower the latency, the fewer of these. This means that there's 
> not merely a "good enough" level on latency (at least not above human reaction 
> time), but rather the lower the better in a very tangible way. This should be 
> a compelling and objective argument.
>
> I'm not aware of any study, but it stands to reason that every interruption 
> results in X seconds of lost productive talking time. Say X = 5s. While we 
> don't know the slope of the function: #_accidental_interruptions = [some 
> unknown slope] x (latency_in_ms - minimal_human_reaction_threshold_in_ms), 
> where minimal_human_reaction_threshold_in_ms probably equals something like 20 
> - 50ms. As soon as latency > minimal_human_reaction_threshold_in_ms, 
> #_accidental_interruptions becomes a positive number and lost productivity 
> also increases at 5s/interruption (using above assumption).

I also think the interruptions will be longer with higher latency as it will be 
harder to sync up.

> Even if there is no such study, this is clearly an easily studyable metric to 
> establish the typical human reaction time (that's probably already known), the 
> mean and median time lost per accidental interruption, and the key piece: the 
> slope of the line or shape of the function that says how many additional 
> accidental interruptions occur for every ms of added latency. Anyone here 
> looking for an academic study with a simple metric to provide data to ISP on 
> economic value in reducing latency that is simple enough that even a 
> high-school kid could understand the meaning, this might be it.

or can anyone setup a simple router/pi image that can introduce arbitrary 
latency and then let's see if we can find some high school students looking for 
a science projct. That may not get the academia stamp of approval, but if we can 
get a bunch of people around the world to test things, we would get data back 
faster than waiting for a more academic process (and it could potentially feed 
into such a process)

it doesn't even need to be a full blown video conferencing program in use, but 
with more people on the call, there's more chance of interruptions.

David Lang


> Cheers,
> Colin
>
>
> -----Original Message-----
> From: Sebastian Moeller <moeller0 at gmx.de>
> Sent: Friday, June 7, 2024 11:33 AM
> To: David Lang <david at lang.hm>
> Cc: Colin_Higbie <CHigbie1 at Higbie.name>; starlink at lists.bufferbloat.net
> Subject: Re: [Starlink] 300ms Telecommunication Latency and FTL Communication
>
> Hi David,
>
> On 7 June 2024 16:55:54 CEST, David Lang <david at lang.hm> wrote:
>> Sebastian Moeller wrote:
>>
>>>> video conferencing is more sensitive to latency than pure voice (in my personal opinion, no study I've read on this specifically), because we watch people's faces for reactions to what we say as we're speaking.
>>>
>>> [SM] I am happy to believe you on this, but ti turn this into something useful for my purpose I will need to find something published, preferably peer reviewed. But thanks to the pointer which should help in my search.
>>
>> one factor to point out, almost all video conferencing is you to server to other user, not direct you to other user. If you have two people in the same house on a call together, they suffer double the latency.
>
>>
>>>> If there is a noticeable lag there, it disrupts the conversation. On the other hand, the same lag in a pure voice discussion, which is inherently less synchronous, would not be noticeable.
>>>
>>> [SM] Not sure I fully agree here, assuming video and audio arrive both with the same delay I would guess both suffer similarly from the delay... my gut feeling is as long as natural speech sequence stays intact, that is no unintended collisions due to both speaking at the same time, audio-only and audio-video should both be sort of OK...
>>
>> the longer the latency, the more likely people are to talk over each other, because they don't see/hear the other person talking when they start. If the latency is low, they can stop quickly, but as the latency increases, they are talking longer before they hear the other person.
>
> [SM] I fully agree, that is what I meant with unintended collisions... and as long as we are in the regime with little talking over each other I expect little differences between the modalities.
>
>
>>
>> 1. this means it's harder to figure out who started first and should
>> continue 2. this means that there is a longer time period of multiple
>> people talking
>>
>> I agree that this is the same video vs audio. That's why I was thinking back to the early AT&T research I've heard from Internet lore (back when AT&T had a huge R&D section). It may be useful to look not only for long distance info (including microwave relays vs direct cables vs satellite relays) but also if they have any research on early conference calling.
>
> [SM] Thanks, will have a look at that as well.
>>
>> David Lang
>
> --
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>