Video Call

Since the invention of radio, Earth has been broadcasting signals out into the universe. The very first signals were extremely basic. AM basically takes vibration and slaps a carrier wave on it. Over time, signals got more complicated, but if you understood how the first signals worked, you could probably guess what changes happened to create the new format. An alien wanting to communicate with earthlings could probably go and sample everything Earth has broadcast over the decades and learn how that new and improved protocol works.

Or comms with a new civilization could start with some exchange of voyager-style basic info about the species, then negotiate an AM signal, then use that to negotiate a more complex signal, until you build up a complex and data-dense signal that both ships are able to encode and decode.

Also, a lot of the complexity of modern signals comes from compression and encryption. Compression because you want to get as much signal as possible through a crowded transmission medium. Encryption because you don't want unauthorized people to access the data. In a ship-to-ship encounter in space you might not need to worry about those two things. You can use immense bandwidth because there's nobody else using that section of space so there's no need to restrict your transmission, and you want to communicate so you'll remove all the encryption that would prevent that.

I'm imagining two super-competent AI speaking to each other like - "Here's three terabytes of our home planet history in annotated pictures, it covers the period since my people first crawled out of the sea, and yea that's why we are using base-14 numerical system, just count the number of the tail spikes. Okay, in three milliseconds the captain will press the communication button, just draw this picture stream however you like, it doesn't matter if you draw left-to-right or right-to-left, you are aliens anyway so you won't tell one fish face from another, and your species see in different color range, so just swap the colors to look fancier, our skin will look to you dull grey in person."

The best part of the movie Independence Day was when the protagonist connects his laptop to the alien ship and see onscreen that they use TCP/IPv4

What are the odds???!

There is a cut scene from that movie where they say that they cracked the alien coding language from the Roswell crash.
- And while I haven't watched the movie in a few years, I recall them saying that modern computers were made using what they learned from the crashed ship.
In-universe, they explain that we originally stole our computer tech from their crashed ship

https://xkcd.com/927/

I know most of you know the reference already, this is for members of today's lucky 10,000

If the only legacy of humanity is XKCD comics I am ok with it

I like the theory of the mathematically obvious RTC protocol, since that would also serve as a sufficient filter for newer races to determine if they are technologically advanced enough. Could they successfully dial in without assistance? Cool let's start chatting now and begin integration with the federation (plus leaves the opportunity of a plot for an almost-ready race that was given illegal assistance, and maybe it's revealed that one of the dominant races was also given illegal assistance when they first dialed in)

In the expanse books and show there is a lag the further away the signal is going, instant if close. Sometimes minutes, sometimes hours. They'll just be video chatting then you'll reply to what someone say, wait 30 seconds for them to recieve it then they start speaking and you have to then wait 30 seconds to get their reply.

Yea I always love that they had a realistic light delay. Even in the show it is that way, and each call has an indicator for what the delay is based on how far away the person you're talking to is.
- Stargate was surprisingly good with this: there's an episode where two members of team SG1 get stuck on a test flight gone wrong, and as they're drifting past Jupiter the radio messages from home base start having timestamps attached to the end, as they're a significant fraction of a light hour away already.

What it means is folks like Uhura and Sato were the most hypercompetent crew members on the whole damn ship, figuring out protocols compatibility on-the-fly.

You kind of see the progression of how communication is handled via the different Star Trek shows.
In Enterprise, Sato has a doctorate and is probably among the few people on Earth who could even approach the position.
In TOS and SNW, Uhura is a specialist, but in the vein of modern military communications specialists. SNW shows Uhura decoding unfamiliar languages, but able to rely on centuries of work in her field so that it is something that someone with a bachelor's degree can perform.
By TNG, a starship with a diplomatic focused mission can fully rely on computer based tools to handle communication. In cases when this breaks down, like Darmok and Jalad at Tangara, there isn't anyone on the crew whose job it is to handle communication issues.
- In Darmok, the Tamarians stranded the captains on the planet and jammed communications. Whether they have a specialist or not, they wouldn't have been able to help Picard, and there wasn't enough context in the ship-to-ship communication logs to figure out their meme-speak anyway. Data and Troi do still figure out pretty quickly that it's a meme-based language, but, again, the lack of context means they don't get far.
- I thought that was part of what Troi did. Don't think it was an official function, but in practice Troi fed info on emotional state to try and support communication (among other things).
  Still not sure why there wouldn't be a backup interpreter if you're a ship on a diplomatic mission, and you're often getting fired on with shit that can fuck up your systems.
  ...oh god, I'm turning into a Trekkie, aren't I? Is this how it starts?!

Try piping an opus bitstream to ChatGPT

Well, I'm sure in the future they would have better tools than either of these.

And even then they shouldn’t be able to communicate at all. The Children of Time series by Adrian Tchaikovsky plays with that a lot.

The only reason the space faring civilisations are able to open communication channels with each other is that they all originate from earth and their technology is at least partly based on what the once mighty humans have left behind.

Which leads to this hilarious chapter in which, after finally being able to communicate with the foreign ships, our characters receive just a pattern of wildly dancing colours and they’re all like wtf? I guess that’s what you get for trying to speak to an octopus.

All humanoid species in Star Trek originate from the same planet, but it's not Earth, it's Progenitor Homeworld https://memory-alpha.fandom.com/wiki/Progenitor
I'm enjoying his Final Architecture books. Some aliens talk with humans perfectly and others don't. The little crab people and giant worm people are fine. The barnacle folks everyone can translate but no one really understands.
The moon monsters and the demon in the warp make it cosmic horror + space opera. Which makes my heart sing. And playing with communication is a real part of it.

In space, everything is so far away, that you can get away with no encryption what so ever when communicating between 2 ships in close proximity.

Sci-fi media always sets unrealistically high expectations for system interoperability.