MelonDS IPC local wireless implementation and a "better" layer 1/2 medium

[aredspy]

It took me a while to wrap around the past couple years of history on MelonDS's local wireless saga, so here's a quick rundown:

1. Upstream MelonDS (after much work) eventually succeeded in making local wireless play possible using an IPC sync setup, which makes games run quite smooth over an ethernet LAN network.
2. MelonDS-android used to have the old socket method from before MelonDS 0.9.5, which was removed due to its instability and inability to work well with the DS's strict WiFi timing requirements.
3. The current (hopeful) plan is to make the new IPC network implementation available on MelonDS-android
4. RetroArch does have this upstream feature in their MelonDS-DS core, but tunnels it over their own Netplay protocol, which makes it incompatible with stock MelonDS or hypothetical MelonDS-android.

Now here are the current issues on why I'm making a new thread (lol):

• Recent DS devices like the AYN Thor, RGDS, etc have left a ton of users wanting the local multiplayer features on original hardware (there are lots of discussions and issue requests)
• Even though MelonDS's IPC implementation works great on LAN, it is still considered somewhat unstable on WiFi due to latency requirements.
• Android does not support WiFi adhoc mode without root (explained below)

Even though the DS only used 802.11b, it did not (afaik) use infrastructure mode when doing local wireless play, and instead used 802.11 ad-hoc (IBSS) which allowed for much better latency due to the lack of a router adding a station hop. iirc, it didn't even load the tcp/ip stack when doing this, so it pretty much ran on 802.11 PHY (See Nintendo UDS Protocol)

Basically, it would be sorta dumb to attempt wireless local multiplayer on a WiFi (infrastructure mode) network and expect it to work flawlessly because the router will add latency and even with modern protocols like 802.11ax, packets aren't guaranteed to be sent so uniformly thanks to CSMA/CA. You could circumvent some of this by having the host run a hotspot, but then you'd also have your friends join your hotspot first, which could get annoying.

Now unfortunately, WiFI ad-hoc mode is not so common anymore due to a variety of reasons which has led many devices that disable it or don't support it (Android). Thankfully, we have WiFi Direct and WiFi Aware which were made to make up for all the cool P2P IBSS wireless tech that was popular in the 2000s lol.

Android supports both out of box with a complete API, and pretty much every modern device supports WiFi direct at the very minimum.

So here's what I'm trying to see what and how to implement:

• A system lib/app that simply adds a nice API and frontend for finding and connecting to devices automatically via WiFi Direct/Aware, and correctly advertising LAN "groups" from MelonDS. You should be able to just setup MelonDS once and have the library auto handle rooms, connections, etc.
• Upstream local multiplayer implementation from MelonDS.

I believe the second is a planned feature that is currently being worked on, but the first one would be a nice way for handheld devices to initiate a low latency p2p connections to each other. Optimally it could be used by any application or emulator for WLAN traffic, or a modern version of spotpass.

Wondering what anyone else thinks of this idea and if I should take a crack at it. I haven't found any existing project that aims to accomplish this, but if there is, please share :)

[rafaelvcaetano]

Thanks for the detailed information. I have started drafting some architectural plans for how to try to implement multiplayer support, but have not made any proof of concepts yet since I want to get other features out of the way so that I can focus 100% on multiplayer. I was not aware (hehe) of Wi-Fi Aware, which seems to be a pretty good way of making multiplayer a seamless experience! However, it also seems to be unsupported by a considerable number of devices, which is a shame. Nonetheless, something definitely worth considering, so thanks for bringing this into my attention!

[aredspy]

Cool, as always thanks for all your work and take your time!

I'll try prototyping some mock up with both Direct and Aware. Luckily they both allow service advertisement, so it can filter which device to initiate connections with. Will also try to take a look at the frames generated by MelonDS with the current basic LAN group server that's available on PC.