Two and a half years ago I wrote a lengthy post about power consumption problems of smartphones and one remedy for it, referred to as 3GPP Release 8 Fast Dormancy. This feature enables the mobile device to inform the network that it thinks that no further data will be transferred for the moment and that it likes the radio link to be downgraded to a more energy efficient state. This way, the timeout period during which power consumption is high can be significantly be reduced. This is very beneficial in cases when only background traffic such as keep-alive pings and email push/pull services communicating with a server produce short bursts of traffic while the mobile is not actively used. Also, another benefit is that the connection is put into a semi-dormant state (Cell-PCH / URA-PCH, see the post linked above) from which it can be reactivated much more quickly than from a fully idle state. Shortly after that post one German network operator actually switched on the feature.
So when I recently made a check of the state of the networks in Germany I was very positively surprised that three out of four networks have the feature implemented and activated by now. Two of them switch the connection to the Cell-PCH state while one uses URA-PCH. Only one laggard remains, incidentally the least performing one in recent network comparisons.
So what's the difference between Cell-PCH and URA-PCH? In Cell-PCH state, the mobile needs to send a cell update message whenever it changes from one cell to the other so the network can send a paging message for incoming voice calls, SMS messages or IP packets via the right cell. When users are moving or are located just in between two cells this results in increased cell update signaling. URA-PCH on the other hand groups several cells into a common registration area (URA = UTRAN Registration Area) thus reducing the cell-update signaling. If this is better than Cell-PCH depends, of course, on how many cells are in an URA.