Multi peer connection using Google Nearby Connection

Question

I am working on my Bachelor Thesis and I have to implement an application using Google Nearby Connection API. The goal is to develop a disaster assistance app.

I tested Google Nearby Connection for the past two day and I have some problems, quesitons.

I have 6 devices, 4 Motorola G (2nd Generation), 1 Nexus 5X and 1 OnePlus 5T. They all are up to date. I also use the latest version of Google Nearby

'com.google.android.gms:play-services-nearby:15.0.1'

Here are my questions:

• The Motorola devices ask for a pairing code to connect one to another, but even when the pairing is accepted they do not connect.
• Some device connect flawlessely (OnePlus and Nexus) but the Motorola have problems connecting, the often throw this error : STATUS_BLUETOOTH_ERROR
• Is it possible to create a mesh application that will forward message form device to device? With the testing I made I am starting to wonder if that's really feasable.
• During my testing I often discover and advertise in the same time. Is there a better way to do so that might avoid problems?

I used the documentation of google and some other ressources I found online. Here is the code I had at the end: Gist Link

Thank's a lot for the help guys!

Answer 1

Disaster assistance apps have actually been talked about a lot on our team, as a really interesting use-case. I work on Nearby, the team that built (and maintains) Nearby Connections. It's definitely feasible, once you know the limitations.

• I believe that Motorola bug has been fixed on our internal builds, so look out for it in the coming months. The update will be pushed out to all devices (you don't need to update your app) in 1.5~2 months. Wish we could push it faster, but it is what it is. They should be connecting if the pairing dialog is accepted, though. If that's not working, I unfortunately don't have a work-around.
• We've found that toggling Bluetooth is the best way to get around STATUS_BLUETOOTH_ERROR, as the radio can get into a bad state (especially on Android versions older than N... which is... a lot of Android versions...). We do our best to toggle semi-often, by toggling the radio after apps stop using Nearby Connections, but sometimes that's not enough. In extreme cases, the phone may have to be rebooted. This error can also go away on it's own, and can also be somewhat alleviated by stopping discovery before connecting.
• Yup, meshes are definitely possible. For an always connected mesh, you'll want to use P2P_CLUSTER. Try to keep 3~4 simultaneous connections per device (and have some kind of logic to avoid forming islands). Once the devices are connected, you'll need to build a protocol to send messages, flooding the network for broadcasts or hoping between nodes for directed messages. Other ways to solve this problem that I've seen are using advertise / discovery to transmit short pieces of information asynchronously, or setting up a timer (eg: Once an hour, everyone scans and tries to connect to exchange data, and then quickly disconnects), or forming a 'snake-like' connection where everyone connects to at-most 2 devices and forms a long string of connections.
• Advertising is usually lightweight, but discovery can be hard on the radio. We turn it off internally while you connect, but we turn it back on for the duration of the connection. This can lead to flaky connections. If you're able, try to limit discovery to short bursts.

PS: You can check my post history to get some more in depth information about Nearby Connections. PPS: In the future, break up your stack overflow questions into smaller, more pointed questions. It's more helpful for people searching in the future.