title: Android Messaging app - Client - Server Communication
body: <p>I want to write a private messaging app similar to Whats App. Smartphones with Android OS shall be the clients and communicating with one server. Now my question is how could that work out? </p>
  
  <p>I guess the best way would be via a Restful webservice as port forwarding is absolutely no option. So what is the better way? - Client asking every few seconds if there are new messages or is there a way how the server can notify the client when there is a new message, and the client just sends a sign of life every few minutes? How does whats app do that?</p>
  
  <p>Would UDP holepunching or reverse TCP any good in this case?</p>