Develop Reference

wifi direct queries

I have 2 queries related to android wifi direct.
I am able to connect my motorola phone with Redmi via Wifi Direct. However when i try to connect my Motorola phone with Xiomi device it fails. So is there some device compatibility issues when working with Wifi Direct? I couldn't find any answer online.
Once 2 devices are connected via Wifi Direct, i don't get to decide which device gets groupadmin role. But only client can send files to server. But how Shareit allows any device to send data in any direction?
Thanks!

Can two processes running on a smartphone communicate with their corresponding apps running on pc at the same time over bluetooth?

I have a Huawei Ascend G700 smartphone. I connect it successfully every time with my laptop via Bluetooth. I have an android application of my own which sends data to a server running on PC via Bluetooth. Whenever I launch my application on my smartphone and try to connect it to the server (already up and running) via Bluetooth, it does not connect.
When I connect my smartphone with laptop via Bluetooth, the laptop automatically starts receiving the phone calls and I can answer them from there.
I tried but was unable to stop this thing from happening. What I suspect is that because Bluetooth channel is already engaged by that call receiving process! that is why my application cannot connect to the server running on PC. Is my suspicion correct? If it is, please help me in solving it.

UDP between 3G connected device and WiFi PC

Is it possible to use UDP over the 3G network? I have tried but failed, I have an application on my PC that reads UDP packets and I'm trying to send UDP packets to that "server" using my 3G connected phone.
These scenarios works:
Local to Local over Wifi
External to External over Wifi
This does not work:
3G to PC

I found the following source. The most important thing for me is:
an iPhone can send UDP packets to hosts off the AT&T network
an iPhone can't receive UDP packets sent to it from a host off the AT&T NAT network
an iPhone SHOULD be able to send & receive UDP packets to other iPhones on the AT&T network.
We should be able to send DIS from an iPhone to a server
We should be able to do multicast on a WiFi interface, and send & receive to other
hosts on the same WiFi network
This should also apply to all other smartphones. If you can not receive UDP packages from your phone the packets could be blocked by your Network Provider, or something in your setup is wrong.
The bigger problems seems to me that you are unable to send data back to your phone. That makes all UDP calls a one way route and maybe render your server useless.

How does a icmp packet (ping command) work in wireless network?

i'm trying to write an app to discover hosts in the network ( like Network Discovery by Aubort), I have a question:
When the android phone send broadcast ping:
-Do the broadcast pings come to wireless router ( or Access point!) and it broadcast them for the phone? And then the wireless router receive and response the ping-echo-reply to the phone?
-If not the phone have to broadcast pings itself and I think not sure that it's signal quality is as good as wireless router's. So how to make sure that the phone have a complete scan in the network?!
(sorry for my poor English >.<)

Broadcast packets are retransmitted by the access point to other wireless clients (as well as to the wired network).

Android - modes of connectivity, device identification and device inter-communication?

Can someone explain a couple of very simple concepts to me - I'm interested in mobile devices running android and how they are identified over networks. Some scenarios:
Device is connected over WiFi - presumably the device has a standard IP address as with any host and can communicate with any other android host over TCP/IP (assuming it knows the participating device's IP?
Device is connected over bluetooth - how are devices identified in this case?
Device is connected over mobile operator's network - this is the one I'm interested in and confused by - is there anyway for two or more devices to discover each other and communicate via the mobile operator's network? How does a device communicate with a backend server in this scenario? In other words, how do apps and devices communicate when not connected to a WiFi network?
Thanks for any advice..

I'm only sure about the bluetooth thing, so i only answer this part:
The Bluetooth interface on your device has an MAC adresse. So while communicationg over Bluetooth you can assume that this MAC adresse is a unique identifier for a specific device. You can also reach other devices by establishing a connection over this MAC adress- However, to get this mac adress in the first place, you have to know it from somwhere, or you have to search for other bluetooth devices in the reachabla area before.

WiFi and 3g both attach the [mobile] device to the internet so it can make internet connections. 3G assigns a publicly addressable IP to the device, so one could, presumably open a server socket and listen for connections. The client would have to know the mobile IP, which may change quite frequently.
Bluetooth is more geared toward close-proximity. Devices in the vicinity can be connected to, after you have paired with them, which requires the cooperation of both devices which are to communicate.
If the goal is to produce an application which connects to nearby devices, I can think of the following ideas:
3g: all devices running the client register their position with a central database server. If the server detects that two clients are in close proximity, let them know so they can connect through the internet or through the server
WiFi: you could use the same idea as 3g, or use broadcast/multicast packets to broadcast your presence. Other apps can listen for those broadcasts and discover which other devices are near.
Bluetooth: A little trickier, as a device must be placed into discoverable mode in order for others to "see it". Discoverable mode is a temporary state and only lasts about 30 seconds (at a time).