When WCDMA was specified, there was little attention to requirements posed by applications whose functions are based on actions initiated by the network, in contrast to functions initiated by the user or by the device. Such applications include, for example, push email, instant messaging, visual voicemail and voice and video telephony, and others. Such applications typically require an always-on IP connection and frequent transmit of small bits of data. WCDMA networks are designed and optimized for high-throughput of large amounts of data, not for applications that require frequent, but low-throughput and/or small amounts of data. Each transaction puts the mobile device radio in a high power mode for considerable length of time—typically between 15-30 seconds. As the high power mode can consume as much as 100× the power as an idle mode, these network-initiated applications quickly drain battery in WCDMA networks. The issue has been exacerbated by the rapid increase of popularity of applications with network-initiated functionalities, such as push email.
Lack of proper support has prompted a number of vendors to provide documents to guide their operator partners and independent software vendors to configure their networks and applications to perform better in WCDMA networks. This guidance focuses on: configuring networks to go to stay on high-power radio mode as short as possible and making periodic keep alive messages that are used to maintain an always-on TCP/IP connection as infrequent as possible. Such solutions typically assume lack of coordination between the user, the application and the network.
Furthermore, application protocols may provide long-lived connections that allow servers to push updated data to a mobile device without the need of the client to periodically re-establish the connection or to periodically query for changes. However, the mobile device needs to be sure that the connection remains usable by periodically sending some data, often called a keep-alive message, to the server and making sure the server is receiving this data. While the amount of data sent for a single keep-alive is not a lot and the keep-alive interval for an individual application is not too short, the cumulative effect of multiple applications performing this individually will amount to small pieces of data being sent very frequently. Frequently sending bursts of data in a wireless network also result in high battery consumption due to the constant need of powering/re-powering the radio module.
Furthermore, in general, mobile application usage is sporadic in nature. For example, there can be periods of user inactivity (e.g., during working hours or when the user is sleeping) followed by periods of multiple application usage, such as where a user is updating their Facebook status, sending a Tweet, checking their email, and using other applications to get an update of their online information. This doesn't mean, however, that the mobile device is inactive during user inactivity: the device may be actively downloading new content such as advertisements, polling for email, and receiving push notifications for activities on the Internet, thus utilizing occupying network bandwidth and consuming device power even when the user is not interacting with the mobile device or otherwise expecting data.