SIB 2
contains information on the available URAs. There can be up to eight URAs in a cell.
LAI: Location Area Identifier: PLMN id + LAC(location area code) = 24+16=40 bits
RAI: Routing Area Identifier:LAI + RAC (routing area code) =40+8 = 48 bits
URA: UTRAN Routing Area: URA = 16 bits
UTRAN cell id: UC id= RNC id + cell id = 12+16 = 28 bits
LA: location area
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 [...]
*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 [...]
