Thursday, December 12, 2013

Staying Online While Mobile: The Hidden Costs

Andrius Aucinas, Narseo Vallina-Rodriguez (University of Cambridge), Yan Grunenberger, Vijay Erramilli (Telefonica Research), Konstantina Papagiannaki (Telefonica Research), Jon Crowcroft (University of Cambridge), David Wetherall (University of Washington)

Presenter: Andrius Aucinas

Motivation and introduction :
The authors study the energy and network costs of mobile applications that require continuous online connection (e.g. WhatsApp, Facebook, Skype). They find that the idle online presence drains the phone battery nine times faster, which can be explained by the high frequency of TCP keep-alive messages, as wells as the cross-layer interaction of TCP and cellular network protocols. The authors propose solving this problem with a two-way push notification system -- with messages being sent at a low frequency and low volume by a network-aware sender.

Measurements and Results:
The authors develop a tool, which they call Rilanalyzer, and they use to perform energy measurements in mobile devices. They show that application that require online presence force the RRC state machine to stay in high energy consumption mode; short messages that are used to keep TCP connections alive have a very high hidden energy cost. This occurs from the facts that mobile platform's push APIs are not sufficient for all applications and that there is not common mechanism to enable applications keep online presence, and therefore application developers prefer to use long-lived TCP connections.

Why you should read this paper:
The authors show how apps, such as WhatsApp and Skype, have a great impact the battery life of mobile devices. They also identify the reasons behind this large hidden cost of these apps, and propose novel ways how to solve them. 

Questions & Answers:
Q1: How you compute the impact of background applications to the battery life.
Answer: We see how much time does the application keep the RRC state machine on high energy. 

Q2: Is there something else that can be done, apart  from using the push mechanism. 
Answer: We must see what are the needs of the applications, in order to find more ways to improve their energy consumption.