The Nokia Siemens Blog writes:
With its latest iPhone iOs 4.2 software, it looks like Apple is joining efforts to cut smartphone signalling down to size. Tests by Nokia Siemens Networks have shown that iPhone iOs 4.2 supports a technology called Network Controlled Fast Dormancy, which we have already introduced into our networks. Basically, the technology makes the network and the handset work together to create the best conditions for smartphones to work quickly, yet have a long battery life and minimize network congestion.
Smartphones connect constantly to the network, often driven by applications. But this creates a huge amount of signalling as smartphones switch from an idle mode to an active state so that they can interact with the network, for example to get emails or pull in the latest tweets.
When it has gathered the information it needs, usually working in the background so you don’t even notice it’s happening, some smartphones then switch immediately into the idle state in order to conserve battery power. So when you next want some data from the network, the smartphone has to reconnect. This involves the network and phone exchanging many small signals.
All this disconnecting and reconnecting takes time and can cause a frustratingly slow network response. On the other hand, leaving the smartphone in an active mode all the time drains the battery very quickly.
To overcome the problem Nokia Siemens Networks introduced a method that, instead of putting the handset into idle or keeping it always active, keeps the handset in an intermediate state. From here, a smartphone can wake up much more quickly and needs to send far fewer signals to and from the network to start a data connection. You get a fast network response and a longer battery life.