Websocket interval: performance problems on mobile

Question

In my current project I discovered a problem using websockets with socket.io and node.js on mobile devices. It seems that there is a problem for mobile deviced handling socket messages in an interval.

I reduced it to a minimal scenario:

The server (minimal express.js server) sends messages to the client in an specific interval:

setInterval(function(){
  socket.emit('interval');
}, 500);

The client just messures the time between the received messages and displays them:

socket.on('interval', function (data) {
  timeElement.html(new Date() - startTime);
  startTime = new Date();
});

On a desktop (using Chrome) the resulting time between the messages is pretty stable at 515 ms. So its like a 15ms delay but message interval is consistent.

On a mobile device (I'm using a Galaxy Nexus with Chrome) the time varies between 400 and 600 ms with some more extrem spikes in either way.

I want to use such an interval as a game turn indicator and this problem results in a lot of lagging and uneven player movement on mobile devices.

Answer 1

You have no promises about when a network packet will get to you. If you're not using a reliable protocol like TCP, you can't be sure if a packet will get to you. Sometimes packets get dropped.

As it happens, you are using TCP (which is the underlying network-level protocol for WebSockets). When a TCP packet is lost, the network must identify the loss, and then resend the packet, causing a delay. It's possible that the mobile device's physical network card simply is more prone to drop packets than the physical card on your desktop.

Network message intervals are a terrible mechanism for reliable timing.

Another -- or an additional -- possible explanation (if you suspect packet loss is unlikely) is that on such a low-power mobile device, the network driver simply isn't getting enough time on the CPU (or is not getting its CPU time quite soon enough), so there are driver-level delays in processing the queue of packets received on the physical network device.

Answer 2

1. Some proxies doesn't allow web socket connections, so in case it doesn't then you need to switch to HTTP.
2. As mobile network is not reliable, it might be possible that your web socket is not live, It will be good to keep checking in some specific period of time that whether connection is active or not. If it is not then establish new connection.