I am trying to obtain information with the usage of UDP protocol on my Android device. I have to consider two cases - connection via access point, and router.
Sadly, in case of access point, I am loosing 95% of data - even though the sending process works properly (I can easily receive that information on my laptop). Somehow Android just can not cope with high traffic sent from one source.
Such problem does not exist when the connection works via router, because then the data is broadcasted from multiple sources, and it works reliably.
I would really appreciate any information about the cause of such behavior.
I have solved this issue - the access point did not detect any device in his network, even though there were few android devices connected. I had to write a pinging service, that keeps the constant outbound traffic.
Related
just want to know is there any methods to allow 2 different apps to communicate. Both of the apps are installed on different devices as well. I had gone throught quite a lot of research, but seem that INTENT, BROADCAST RECEIVER failed to meet my scenario. INTENT, BROADCAST RECEIVER can be work if both of the apps installed on the same device.
Here i can say you can use to make your things work :-
Sockets are typically used to accomplish this between Android devices (or between any peer devices).
When two devices desire to interact, you configure one or both of them to "listen" for connections on a socket and accept a connection from the other when that happens (or you can have a dedicated client and server and the client always initiates the connections).
You can exchange messages after the link has been made.
Android client server socket applications come in a variety of forms, but one that I found handy was:
Example of Android Server/Client using Socket on the client side (and its companion server side blog article - link included in the client blog)
It should be noted that you might need to add your own "protocol" on top of this. For instance, if you are sending a file that is unknown in length without a special "end" character, you might want to add a byte (or several bytes to represent an int, long, etc.) at the beginning to indicate the length of the transmission so the receiving side can tell when it has received everything (or that it has not received everything in case of an error).
connecting via networks (such as most 3G/4G) that forbid inbound connections
Even though there is nothing theoretically blocking sockets from functioning in these situations, many mobile operators will not permit inbound socket connections in practise. You would also need to determine the mobile's public IP address, which is doable but adds complexity. Whether your solution will only ever operate on a single operator's network, you can test it out to see if it works; but, if it doesn't, you could discover that using a server in the "middle" is preferable and easier: Devices A and B establish connections with servers Device A "discovers" device B after requesting the addresses of connected devices from the server. Device A sends device B a message.
Actually, it indicates that the messages should be forwarded to device B while sending them to the server. Device B is informed by the server that a message is available for it (using some sort of message notification like Google Cloud Messaging for example, or simply by the devices polling regularly to see if they have any messages). Device B accesses the server and downloads the messages. The aforementioned will function on pretty much any network that permits internet connectivity. It does have the drawback of having a server, but for the majority of mobile networks, it is probably a necessary approach.
You make one app a server using ServerSocket.
You make the other app a client using a Socket.
With both devices in the same network the client can connect to the server knowing its local ip.
After connection established they can communicate.
Nearby Share sometimes uses bluetooth to transfer the files because of which it is very slow. Sometimes it is not at all handy to transfer files that are more than 100 MB. Initially I thought Bluetooth is used only for handshaking purposes. But later I realized that the files are itself transferred via bluetooth. I'm curious to know why should the files be transferred via bluetooth when it can be transferred via wifi direct. A lot of third party apps including Google Files use wifi direct to transfer the files. So why does a built-in functionality like Nearby Share should use bluetooth. The sole purpose of Nearby Share itself is to achieve fast file transfer with wifi direct and without internet. So if the files are transferred via bluetooth there is no point in using Nearby Share.
I'm also curious to know the various modes of file transfer present in Nearby share. There are three modes: Data, Wifi Only and Without Internet. I'm really curious to know why is an internet connection required to transfer files when Nearby Share is meant for file transfer without Internet. Is it meant for handshaking purposes in Web RTC?
(Disclaimer: I work on Nearby Share)
Nearby Share will always attempt to upgrade to WiFi before sending files larger than 1MB. A grace period of 10sec is given for that upgrade before fallback mechanisms kick in and the file is sent over Bluetooth as a last resort. Even after falling back to Bluetooth, the devices will continue to attempt to upgrade to WiFi in the background, but some failures are unrecoverable and the file will fully send over Bluetooth. Note that urls and very small files will immediately send over Bluetooth.
This upgrade can fail for a multitude of reasons. Most commonly, it's a concurrency issue. The same radio is used for Bluetooth, p2p WiFi, and your normal access point connection and it must be time-shared accordingly. If all 3 want to be on different channels, you will miss messages -- it's a guarantee. If these messages are important, such as the authentication frames when connecting over WiFi Direct, then the connection will fail. If these messages are less important, they may be resent until successfully received, but it will lower throughput for the transfer such that even 5GHz WiFi can look to be as slow as Bluetooth.
Nearby Share tries to avoid this in a few ways. When regulations allow, we will attempt to start the WiFi Direct group on the same channel as the access point. This way, the phone doesn't have to timeshare (although it does have the side effect of colliding with messages from the access point. But generally, both sides will back off a random amount and retransmit, and the loss is less than the loss of multi-channel concurrency). Unfortunately, many countries do have regulations that allow certain (or all) 5GHz channels only indoors -- in those cases, the access point can be set up to utilize it but WiFi Direct cannot.
We also prefer mediums like WiFi Direct over Hotspot, as WiFi Direct commonly uses CTS2SELF frames to advertise "Do not transmit for this duration". Unfortunately it's not as straightforward a message as "I am going off channel, do not try to communicate with me" -- CTS2SELF has the side affect of quieting all communication over the access point even if it wasn't directed to the phone -- but it does get the point across.
We pause any Bluetooth activity we have control over, to reduce the need to timeshare with it. In some severe cases, where the OEM has implemented timesharing that's too aggressive, we will turn off the Bluetooth radio to forcefully interrupt Bluetooth activity, but this is disruptive and usually a bad user experience.
We may try to send the data over your access point itself instead of setting up WiFi Direct. This can avoid the MCC situation described above, but comes at the cost that the data needs to be re-encrypted (because we don't know what other devices are connected over LAN and might be eavesdropping), and it does introduce another hop, as the data needs to go through the AP even if the devices are side-by-side. TDLS helps avoid that last issue, but it has limitations (eg. it won't use 40/80/160MHz bandwidth if the AP isn't set up for it, and it'll send over 2.4GHz if the AP is on 2.4GHz).
Other possible failures include the device getting into a bad state (toggling airplane mode can help here), the Android version being too low (ideally both devices should be R+, as it's almost impossible to fix bugs on older Android OS versions, even though we try), or just bad luck.
I am working on an app that uses peer-to-peer communication between Android devices. It receives and delivers JSON data and the data never goes through the server ever. The server is only used to keep track of user IDs, login times, IP changes, and other stuff. This app will use sockets for communication.
Requirements
JSON data goes directly to an Android device from another Android device without going through server.
The android devices can be connected to any kind network like 3G or Wi-Fi (here I assume I have to use NAT).
Server is used to keep track of IP changes of the Android devices as they may be connected to any kind of network.
Challenges
The main problems I am facing are:
I don't know how to connect two devices if they are behind a Wi-Fi network.
What approach I can use if I am going to use P2P for delivering JSON data.
Update
For this I have to use hole punching. The idea I got is that no one can connect to a device from the outside. It must start communication from inside the device. So if A request server S for address of B, then server gives the address of B to A and vice versa. Now what? What occurs next?
Any suggestion would be greatly appreciated.
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'm trying to figure out what the solution is to having multiple android devices on one network share data.
Assuming all of them are running the same app, and a user "registers", I'd like to figure out (without any user input) what other devices on the network are available to be talked to and then to send them this registration data, so that when the user goes to the next device, their info is already there.
I'm able to ping the 255 connected devices in the x.x.x.0-255 range to see which respond, but am not clear on how I can write an app resident server (using the term loosely) that I could then send the data to.
I can't be the first person to need to solve this problem, but am unable to find anything useful on this front.
One caveat is that this is for devices that have no 3G (or other means) of getting to the internet, and the wifi network they're on won't have access to the internet either, so the solution has to be 100% internal network and can't include any additional devices (like a box running apache that all the device can use as a server).
TIA
but am not clear on how I can write an app resident server (using the term loosely) that I could then send the data to.
Create a Service that has code that opens a ServerSocket and listens on incoming requests, such as an HTTP server.
On the whole, this is dangerous, but for constrained circumstances -- such as your "100% internal network" -- it should be safe.