RA: routing area

URA: UTRAN routing area

The aboves are the collections of cells.

LA and RA are for CN to track the movement of the UE to facilitate the paging of the mobile when an active radio connection is not available.

A cell can be in up to eight different URAs.

URA size depends on the UE’s velocity. Fasting moving UEs should be in a large URA to make less URA update.

*Idle mode: CN-level

UE is identified with TMSI (temporary mobile subscriber identity)

*RRC connected mode: UTRAN-level

UE is identified with C-RNTI and U-RNTI

Cell_FACH and Cell_PCH: every cell change needs to be reported via cell update

URA_PCH: every URA change needs to be reported via cell update

(less signal overhead from UE perspective, but more paging messages need to be injected into multiple cells)