Sending data in Android WiFi Direct service discovery instead of connecting

Question

Following the documentation here:

http://developer.android.com/training/connect-devices-wirelessly/nsd-wifi-direct.html

It appears to be possible to broadcast data to all nearby devices that have WiFi Direct without establishing a connection by just putting the data in a WifiP2pDnsSdServiceInfo object. This works for my purposes as I'm attempting to establish a simple P2P messaging app amongst multiple nearby devices. However it seems like a misuse of the API as this is intended to carry information to setup a connection and advertise a service. My questions are:

• What are the pros and cons of sending data this way (please ignore security)?
• Will there be delays in messages being sent/received.
• What will the impact on battery life be like?

Answer 1

• The key/value pairs you pass into WifiP2pDnsSdServiceInfo object are going to be encapsulated into DNS multicast messages, as specified in DNS-Based Service Discovery.

• Multicast traffic on WiFi is especially expensive, so it is not recommended to use this for messaging. Only for critical things like service discovery.

• Depending on implementation (android), the under framework may pool all service discovery records/responses, before it calls your callbacks. This can add significant (even unpredictable) delay for your simple P2P messaging.

• This is basically a DNS messaging, so your "messages" may be cached locally. DNS queries could also try mid-level optimizations like pooling, retries, query filtering, prioritization etc.

• There is no reliability guarantee so your messages may be lost.

• Multicast traffic, which is used here, can result in significant battery drain on android, see here