发现WiFi直接服务 - Windows <=> Android

Question

Long story short

I am trying to discover (Android) devices from a Windows 10 computer, using WiFi Direct Services - but it seems to me that Windows and Android do not agree on the standard here.

When I write Wifi Direct Services or Wifi Direct Advertisement, I mean the feature where a WiFi Direct capable devices can broadcast what services it offers, so potential peers can scan for available devices / services before they make any connection.

Have any one had any success with this across the Windows-Android gap?

Details on what I have tried

So I have been working a bit on this, searching for documentation and examples.

Android <-> Android

Using this Service Discovery example for Android , I have had success with making two Android devices find each-other and list their available service(s) before any actual WiFi Direct connection was made.

The way it works is that a device that want to find other devices (services) will broadcast probe requests. A device publishing a service will then see these probe requests and respond with a probe answer. The probe answer include Bonjour(-like) information informing the first device about available services. This is (similar to) active scanning.

Enter Windows 10

I have been playing with the WiFi Direct Services example project (and others) from Microsoft - but without the big success. Windows is able to see the Android device(s) but

• only if the Android device is in Service Discovery mode (ie sending out probe requests)
• Windows is only able to see the device, not which services it provides.

Basically my conclusion (a bit of guessing) is that Windows 10 uses passive scanning and thus (erroneously?) reacts to the probe requests of the Android devices (when Windows should actually send out probe requests itself and react to probe responses).

So, actual question

I am having trouble forming one clear question, sorry, but

• Has anybody successfully made a service discovery between Android and Windows?
• Does anybody have any insight into how Windows (10) works here? Can I make Windows use the active scanning mode and parse the service announcements?
• Other hints that will help on my way is greatly appreciated :-)

Answer 1

I have done this using an Apple Bonjour server running on the Windows side (Bonjour == Apple's implementation of Zero Configuration Networking).

The catch is that I had to use Mono.Zeroconf library to pull it off http://www.mono-project.com/archived/monozeroconf/ , and it's a little off the well-trod path because the most popular libraries for this on Windows side are client only and do not allow for registration as a service provider. Also, and as an added surprise, the source in this project hadn't been recompiled recently when I found it. It works though -- I just had to recompile it to get it working with .Net46.

Anyway, the operative point is that Android's Network Service Discovery is interoperable with ZeroConf as they are both DNS-SD based and I've been quite happy with the results after finding out most android devices don't do MultiCasting

Answer 2

Just for some context to anyone finding this question, the Windows API you linked uses a Wi-Fi Alliance standard called Wi-Fi Peer-to-Peer Services (P2Ps) for service discovery in probe requests and responses. A service is advertised and discovered over Probe Response frames when a matching hash is included in a Probe Request frame. The services may also be discovered over ANQP/GAS frames with the type P2Ps.

The Android API uses service discovery as defined in the Wi-Fi Alliance Wi-Fi Peer-to-Peer (P2P) standard. This is a form of service discovery that predates P2Ps. It uses ANQP/GAS frames with the type Bonjour or UPnP.

Both methods are valid and standards based, but they are not compatible with one another. The closest you can (likely) get to compatibility is by using Wi-Fi Direct and no service discovery (you can only see device names essentially at discovery time, rather than a "service").

Windows sample: https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/WiFiDirect

Android sample: https://developer.android.com/training/connect-devices-wirelessly/wifi-direct.html