Staying online while mobile: The hidden costs

Mobile phones in the 3G/4G era enable us to stay connected not only to the voice network, but also to online services like social networks. In this paper, we study the energy and net-work costs of mobile applications that provide continuous online presence (e.g. WhatsApp, Facebook, Skype). By com-bining measurements taken on the mobile and the cellular access network, we reveal a detailed picture of the mech-anisms selected to implement online presence, along with their effect on handset energy consumption and network sig-naling traffic. We are surprised to find that simply having idle online presence apps on a mobile (that maintain con-nectivity in the background, with no user interaction) can drain the handset battery nine times more quickly. This high cost is partly due to online presence apps that are exces-sively “chatty”, in particular when their design philosophy stems from a similar desktop version. However, we also find that the cost of background app traffic is disproportionately large because of cross-layer interactions in which the traffic unintentionally triggers the promotion of cellular network states. Our experiments show that both of these effects can be overcome with careful implementation. We posit that a two-way push notification system, with messages being sent at a low (regular) frequency and low volume by a network-aware sender, can alleviate many of the costs