Communication between two Android devices

Hello!
Now there is a question one would like to ask the following:
I now want to achieve this function: there are two Android OS devices A and B, as a client I want A, B as a server, A device can initiate B device camera function (via wifi and 3G network via two way), and can display a video camera to capture the contents of B equipment (no pictures), and can initiate voice calls between two devices in the A device. I wonder if I have clear description is not clear, simple point talk is based on the Android system device, a device can control another device and can communicate with each other, what friends have done this project hope to provide some guidance about or ideas, thank you the!

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After the device is set to achieve B Radio listeners can listen to the broadcast as a function, but you can prepare this broadcast semaphore set Why?
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cited a floor AA5279AA reply:

B radio listeners can set the device to achieve the above functionality after listening to the broadcast, but the amount you are ready to set the broadcast signal why ?

Hello!
You said "broadcasting semaphore set why" I do not understand, is that how to receive the broadcast signal to trigger it? I am also new to Android development soon, I hope a lot of guidance! Thank you! In addition, you can realize the idea of ​​entire functions briefly describe it?
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You can keep in touch with UDP heartbeat packets between A with B, but not on a LAN if the two machines under more difficult, because the mobile Internet is constantly changing IP, you may need a third party to make A and B know each other's IP .
A B calls when he wants to send a UDP packet to B, B will start after receipt of a TCP server, while back a UDP packet to A. A reply is received after the package is set to put their own TCP client, connect to the server, this time you can transfer the data.
One-way video plus two-way audio with FFMPEG can be achieved, but this network and CPU load heavier than. I suggest you put the video hardware compression later transmitted via TCP, A receipt is displayed after the data hard to extract. In fact, you get the data from A to B on the camera, you can achieve pictures and videos on A.
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Beg! ! ! I also want to learn about ...
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I tried on an Android device outside the IP network monitoring, this is not enough, in the 127.0.0.1 from service on another device via the external network also Rom.
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references, 5th Floor fallencity2011 reply:

I tried it on an Android device outside the IP network monitoring, this is not enough, starting at 127.0.0.1 on services another device via the external network also Rom.

Mobile IP and port changing all the time, and certainly not to do so, there must be a server.