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I need to keep a TCP connection established indefinitely (as far as possible). Is not an own server so we cannot change the way it works. This server needs some kind on ping each minute to know that the connection is alive. If the server do not receive the ping after some minutes (less than five), the connection and the session is closed. In this way i need to maintain a TCP connection with the server and be able to send pings at the periods specified.

At the moment i have an Android service with the flag "ongoing" so Android should not kill it (at least by normal procedures). The android service seems to run fine and the pings are sent periodically. However when the service is running on a mobile phone (not emulator) and it gets idle, android seems to freeze the service while the CPU is sleeping, so the TimerTask sending pings stop working and the connection goes down.

I have tried to lock the phone from going to sleep with a partial wake lock and it solves the problem but the phone consumes too battery, what is unfeasible.

I noticed that the AlarmManager may help on this task, so i want to schedule an alarm to update the running service and then send the ping. This will let the CPU going to sleep and also the ping being sent. But schedule an alarm each minute may be also so battery consuming or not?

I have not tested this approach at the moment, but is feasible? is there a better way to keep this kind of TCP connection?. How android services like Gmail solves this kind of issues?

Alvaro Luis Bustamante
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3 Answers3

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I need to keep a TCP connection established indefinitely with a server.

Why?

For starters, it is technically impossible. Users will switch between networks (e.g., was on WiFi, failed over to 3G), users will leave areas where they have Internet coverage, users will turn on airplane mode, etc.

At the moment i have an Android service with the flag "on_course" so Android should not kill it.

There is no such concept as "on_course" in Android. Android services can and will be killed by users (task killer, force-stop in Manage Services) or by the OS. And, since this will be an everlasting services, your users will kill your service if they do not understand what value it is continuously delivering.

I have tried to lock the phone from going to sleep with a partial wake lock and it solves the problem but the phone consumes too battery, what is unfeasible.

Correct.

I noticed that the AlarmManager may help on this task, so i want to schedule an alarm to update the running service and then send the ping. This will let the CPU going to sleep and also the ping being sent. I have not tested this approach at the moment, but is feasible?

Sure. You will still consume too much battery, IMHO. Please allow your user to control your polling period, with a wide range of options (e.g., 10 minutes, 30 minutes, one hour, never).

How android services like Gmail solves this kind of issues?

They use C2DM, which is part of the OS and took a lot of engineering to get right. There was a presentation on it at the 2010 Google I|O conference -- the video should be on YouTube. Note that they do the heartbeat ping every 30 minutes IIRC, and they optimize for the case where the device is on 3G (to allow the WiFi radio to turn off after inactivity).

If your objective of your permanent connection is to implement a push-style communications channel, please consider using C2DM.

CommonsWare
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  • Thanks you! great comments. "on_course" really means "ongoing" :) I really cannot change the frequency of pooling period since it is really strict (i cannot change how the server works) and i need to maintain the connection alive. If i let the user select other period they will be disconnected. I will test how the battery supports a 1 minute period. I hope this will be better than the partial wake lock. – Alvaro Luis Bustamante Jul 30 '11 at 13:45
  • I know C2DM is the best option but I want to get the same functionality just for fun/experimentation. I've used wireshark and it says that C2DM does use TCP but I don't know much else. Where did you see the details about their heartbeat, I would like to learn more. – Nathan Schwermann May 01 '13 at 03:12
  • @schwiz: Most of what we know about the "details" comes from that 2010 Google I|O presentation I mentioned in the answer. – CommonsWare May 01 '13 at 11:19
  • @CommonsWare ok thanks that was helpful. I've implemented my own push sync example now, it is able to maintain a background tcp connection and wakeup the device on incoming messages with zero battery impact. https://github.com/schwiz/android-websocket-example – Nathan Schwermann May 18 '13 at 18:40
  • Does incoming network traffic wake up a device from deep sleep?http://stackoverflow.com/questions/34692417/does-incoming-network-traffic-wake-up-a-device-from-deep-sleep – pvllnspk Jan 09 '16 at 10:45
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You can wake phone from idle with partial wake lock right before you execute ping and after you do it release wakelock. It will scientifically reduce battery consumption and it will do the job. Also, try to increase ping time as long as you can.

Andro Selva
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Ivan Stankovic
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5 Minutes is a little short for the ping time, can you configure the server to hold the connection longer? 30 minute ping or higher would be ideal. Here is an example of an application that holds a background tcp connection and will wake up the device from a deep sleep on incoming tcp traffic. https://github.com/schwiz/android-websocket-example

Nathan Schwermann
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