Location Update
If the LAI or RAI read on system information has been changed then the UE tries to do RAor LA registration Update
• During the idle mode when the UE changes its location or routing area it should do LAU or RAU
• LAU and RAU managed by CN
Example :LOCATION UPDATING
1-The UE reads from system information that the LAI is not the same as that stored in the USIM.
This triggers UE to update the location area.
2-The UE tries to access the network and sends a request message to the RNC, via the RBS
The RNC checks if it is possible to allocate a dedicated channel to the UE.
3- Resources in the RBS and over the Iub interface are reserved by the RNC and are ACK by the RBS
4. Information about the new channel is sent to the UE with a setup message.
5. Synchronization is achieved between the UE and the RBS
6-The UE sends the request to update the location information to the CN.
This message also carries the IMSI and old LAI.
Iu signaling bearer is set up between the RNC and the CN.
There is now a signaling connection between the UE and the CN.
As this is the first time the UE accesses this service area (the subscriber is unknown in the VLR).
7-The VLR sends a request to the subscriber’s HLR for Authentication Information.
8- The HLR sends this information to the VLR(Subscriber is OK).
9-MSC/VLR starts to authenticate the subscriber.
This message is transparent over WCDMA RAN.
10-After Authentication, the VLR asks the HLR to update its Location information for the IMSI and with the new VLR address
11- VLR receives an acknowledgement from the HLR.
12-The MSC/VLR transmits an acceptance to the UE, UE updates the location information in the USIM.
13- The signaling connection is released.
Types of Updates
-Periodic
Occurs periodically after timer T3212 for LAU or T3312 for RAU
The value of the timer sent to the UE over BCCH
CN parameter.
when the UE is in connected mode and the timer expired then the UE wait until enter idle mode again to perform the periodic LA
-Normal
Occurs when the UE change its LA or RA, the UE discover the changes after comparing the new Cell RAC or LAC with the stored values in the USIM
LAC Planning Principles
IMSI attach and detach
-IMSI attach occurs when the UE activated and the detach occurs when UE deactivated
-This function used to prevent unnecessary paging for the off UEs
-IMSI attach is an optional function and it is managed by cell parameter called ATT sent to UE over BCCH
-If ATT set to 1 it means the UE should do IMSI attach and detach
Paging
Is the process through it the CN inform the UE there is a service request or RAN inform all the
UEs that the System information has been updated
- Paging occurs in the following states
* Idle
* Dedicated
-Paging in Idle mode
*PICH and S‐CCPCH are used to page the UE
*PICH used to tell the UE when to read S‐CCPCH
*S‐CCPCH used to carry RRC message type1 which includes actual paging info and the number of times the WCDMA RAN will retransmit the paging
-Paging in dedicated
When the establish connection between UE and RAN is existing Paging type 2 message are sent to the user it is carried on DCCH so it is only for one user.