I am developing currently an Android application that will communicate with other Android devices per Wifi. The Wifi will also provide the online connection. There is no server in this Wifi environment.
The idea was that the devices will discover each other with UDP multicast messages. But we noticed that UDP multicast often does not work on the devices. Sometimes it does, sometimes not.
To work around this issue we implemented a mechanism where the devices will store the local Ips online so that other devices will be able to retrieve them.
But this, of course, does only work if the Online State is available, which sometimes is not.
My question is, if there are other techniques with what the devices are able to connect per Wifi to the each other without knowing it´s Ip in the first place. Is there an easy way to forward the addresses per Bluetooth for example? Or could Wifi Direct be an option?
Every idea is welcome. Thanks for all of your help.
A zero configuration networking solution might work for you. There is a Nuget package called zeroconf that should work with Xamarin:
https://www.nuget.org/packages/Zeroconf/
Source code:
https://github.com/onovotny/Zeroconf
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I'm in the design phase of an Android application that will require a connection to multiple wifi networks, and I'm wondering if anyone can provide advice and/or code snippets regarding the best way to go about this. The app will have a connection to one wifi network that has internet access, and another wifi network with no internet access that will be used to share data accross the devices (raspberry pis) on it.
Can I be connected to both networks simultaneously? If so, how do I specify which network to use when making a request? I've been reading the Android 5.0 documentation which indicates its possible, but I'm a little confused on how to implement it.
If its not possible, this post from 2011 says that the WiFi Direct standard could be another solution. WiFi Direct is now supported on Android, but I can't find many examples of how to use it to achieve my goal.
Any advice is much appreciated!
As far as I know, you can have only one connection to the Access point, meaning that you can indeed make the device connected to the access point which offers you the internet connection, but then you can not connect to other networks.
Anyway, I would suppose that in your use case that is not the problem, actually I don't see any problems there. At least, if you simply have the connection and then have the Raspberry Pi's connected to you, i.e. you simply create a access point in your Android device, and all devices connect to it.
My question is that is it possible to send and receive data between multiple android devices via broadcasting over wifi without establishing p2p connection?
Our professor asked us to design a wireless network system in which you broadcast a message within your android phone, and the other android phones nearby receive it and broadcast it again so that the other phones can receive it and it continues like that. In this way, for example, when someone writes a message in a classroom or café everyone will be able to receive it and broadcast it again. (like an adhoc network system). And although my professor believes it can be achievable, I didn't find anything online like this kind of android network system. So my question is again is it possible to do something like that?
Any helpful leads and references will be appreciated.
Edit: I had to change the title of the question.
I couldn't find a proper solution so I tried the following method so far: I set up a UDP messaging app using Wifi hotspot (it works perfectly for multi clients). The phone who turns on the hotspot is the server and others who connect to it are the clients. Then, I decided to turn this system into an adhoc-like system where there would be more than one hotspot and the clients would connect to them in cycling order and serve as a bridge among these servers.(every second, they will switch to other hotspot and vice versa.) So, they will carry the messages from one network to another. (I know it is very inefficient and prone to time delays; but it is the only idea I have come up with so far.)
When I told this system to my professor, he said that it is too complicated and I just need to broadcast a message from a device to a common channel(without setting up a network connection), and other devices will listen to this broadcast channel(without connecting to a network system), receive the message and broadcast their own messages along with received ones to this channel again as I described in the question body. (he never mentions hotspot, Wifi direct, and etc.) He even told me that the only thing I need to do was to think simpler and use the properties of 802.11. But, I do not think it is that easy to set up such a wireless system, at least for Android where ad hoc systems are not supported yet. So any help will be greatly appreciated. Thanks!
The Nearby Connections API in Google Play Services released last week uses WiFi multicast: https://developers.google.com/games/services/android/nearby
It works for devices already on the same WiFi network. However, it uses a host/clients model, and doesn't work with WiFi direct or a tethered hotspot connection.
You could also use the WiFi direct APIs from ICS: https://developer.android.com/guide/topics/connectivity/wifip2p.html
You can have multiple devices connected together via WiFi direct, so firing UDP packets as #willis suggests would seem the way to go
It is implementable. Do you know the aircrack? similarly, you can receive all packets even not sent to you, and you can send any kinds of packets even not sent by you.
I am working on one project in which two android devices which are in different network need to transfer some data. Both device will have internet connection. It will be either Wifi or GSM provider.
Consider the following cases:
If one Android device has GSM network and
another device in some other place which has Wifi network
If one Android device has GSM network and another device has GSM network
How to transfer data in such cases?
I don't want to use server in between.
Please let me know how do I solve this issue. Any clue or any links which will help me. So far I didn't find any such things. Please help me...
Short Answer: You're going to have to use a server.
Long Answer: You could use bluetooth if the location is close enough or maybe Wifi Direct although I haven't personally used the latter. Although, ultimately a server will be the best option. If you don't know a lot about backend development I could recommend parse.com as a good service that makes creating backends very easy and has fairly high usage limits before you have to pay.
Unless a device has been configured with an external IP address, which is very unlikely (impossible?) on a cellular network, there won't be a way to directly contact it from an external device. Even on WiFi, most devices will never have an externally defined address.
If you had administrative control over a directly connected and externally addressed router, you could port-forward traffic to a single device, but that's likely not the solution you're after.
A much easier approach is to use one of the services that let you define a back-end w/o a lot of setup or costs. The most popular one is probably Parse.
I have an android app, it does the following:
Connects with a server to read and update a database at the same time as others.
I want to convert this to an app that does not need an internet connection. Therefore i would like to know if its possible to have an android device acting as the server with the database, whilst multiple phones connect to it via bluetooth getting and updating the information in the database?
Thanks
Yes. It possible.
However all of your devices will have to be located nearby, so they can connect to each other through bluetooth.
You can take a look at Android Bluetooth API.
However, my recommendation would be to use Wifi instead of Bluetooth. YOu will need additional WiFi router. However, you won't need to deal with Bluetooth API in such case.
You will only need to write a server on one of Android device and the rest of devices will work the same (as now)
There are a few options to doing so, that don't involve a server. Both of them require a slightly different approach than both devices connecting to a server.
Wi-fi Direct- Only available with Android 4.0+.
Bluetooth
Personally, I have been using the Bluetooth option, and not found it terribly difficult. Essentially, you have to do the following to make it work.
Have one of the devices listen for a connection. If it is unpaired, you will have to make the device discoverable.
The second device needs to initiate a connection. It can do this by looking at the known devices and trying to connect to one, or listening for a new device
After the two devices connect, they must initiate some kind of a communication protocol. The communication is essential a serial connection.
Blue-tooth requires that the devices be within about 10 m of each other. Wi-fi direct will allow somewhat further, but as mentioned, is less supported. It is possible to allow for both communication methods, but is somewhat challenging.
Is there a way to go about getting 2 android phones to communicate to each other locally without going through a central server? Sort of like being on WLAN? I need these 2 phones to be able to sync themselves to each other when they are nearby and running the same app.
Maybe through bluetooth perhaps? Just a suggestion, I'm not sure how to go about this, but an idea might be to have each app broadcast through a certain port on LAN whilst searching for the other's broadcast through the same port. Once the other device has been identified, then transfer the data.
The only ways to do that with WLAN environment (and not included a AP i.e infrastructure mode)
Ad-Hoc mode (Google will help you more on this)
Wi-Fi direct - that is the future of peer-to-peer with WLAN. (Again am sure Google will be more than happy to help you!)