Hi dear,
A tracking area update (TAU) procedure can be initiated by eUEs in
both idle and connected modes. TAU can be classified into common TAU and
periodic TAU. The current TAU period set on the enterprise network is 54
minutes.
An eUE initiates a common TAU procedure to notify the network side
of its TA information and EPS bearer status. The network side then synchronizes
the local parameters with those reported by the eUE, and determines whether to
allocate a new TAI list to the eUE.
The periodic TAU is performed at an interval specified by the
T3412 timer. When an eUE leaves the connected mode and enters the idle mode,
the T3412 timer is started. The length of this timer can be set on the eCN.
This timer is carried in the Attach Accept or TAU ACCEPET message.
An eUE performs periodic TAU to notify the eCN that the eUE stays
in the listed TAs. If the eCN does not receive a periodic TAU message from the
eUE within a period of time (equals the length of the T3412 timer plus four
minutes), the eCN determines that the eUE has moved out of the listed TAs or
that the eUE has been abnormally switched off. Consequently, the eCN releases
the resources occupied by the eUE.
An eUE initiates a TAU procedure in the following scenarios:
l The TA
of a registered eUE has changed. That is, after a cell reselection or handover,
the new TA is not included in the TAI list.
l The
T3412 timer expires. (This scenario occurs only in the RRC IDLE state.)
l The
eUE's RRC connection is released due to the cause "load re-balancing TAU
required."
l The
network capability or DRX parameters for the eUE have been changed.
l A
registered eUE moves to an uncovered area, and the local EPS bearer for the eUE
is deactivated. The eUE then moves to a covered area.
l The
eUE performs an inter-RAT cell reselection, and the user-plane data is not
buffered.
PS: eUEs support the TAU procedures triggered in only the first four
scenarios.
thanks
