RRC Service States

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The two basic modes of an UE are idle and connected.

The UE in connected mode can further on be in four different service states, which define what kind of physical channel a UE is using. Today we supports two of them, CELL_DCH and CELL_FACH.

When an idle UE has found a PLMN (see chapter below, initial cell selection and reselection) and a suitable cell to camp on, there is no signaling connection between the UE and the network. The UE is only reading system information and paging indicator.

It also performs measurement on neighboring cells and on own cell and uses the measurements together with the parameters from system information to perform cell reselection. In idle mode it is the UE itself that make sure that it is camping on the most suitable cell for a connection.

If the UE detects a change in LAI, receives a paging message or sets up a mobile originated call, it turns from Idle to connected mode. A change from idle mode to one of the four different connected states is always initiated with a “RRC connection establishment” from the UE to the RNC (see chapter regarding establishment of RRC Connection).

In idle mode the UE is only known in the MSC with IMSI, TMSI or P-TMSI while WCDMA RAN has no information at all until this first message, when the UE asks for a radio establishment.