Content for  TS 23.221  Word version:  18.0.0

For the mobility functionality five different area concepts are used. LA and RA in the CN as well as UTRAN Registration Area, GERAN Registration Area and Cell areas in the RAN.

For CS services, the CN uses LA. LA is used e.g. at CN initiated paging related to CS services. A CS service related temporary identity, CS -TMSI, may be allocated to the UE. This temporary identity is then unique within a LA.

For PS services, the CN uses TA or RA. TA or RA is used e.g. at CN initiated paging related to PS services. A PS service related temporary identity, P-TMSI or S-TMSI, may be allocated to the UE. The P-TMSI is then unique within an RA. The S-TMSI is then unique within one or multiple TAs.

RAN internal areas are used by the UTRAN when the terminal is in RRC-Connected mode (see clause 6.7). The areas are used at e.g. RAN initiated paging. RAN internal area updating is a radio network procedure and the RAN internal area structure should not be visible outside the RAN. In RRC connected mode, the UE position is known on cell level or on URA/GRA level. RNTI is used as a temporary UE identifier used within the RAN and allocated at RRC connection establishment.

The following area relations exist (see Figure 6.3):

• there need not be any relation between URA/GRA and LA respectively between URA/GRA and RA. The URA concept is defined in TS 25.331 and the GRA concept is defined in TS 43.051;
• one RA consists of a number of cells belonging to RNCs that are connected to the same CN node;
• one LA consists of a number of cells belonging to RNCs that are connected to the same CN node;
• one TA consists of a number of cells belonging to eNodeBs that are connected to the same CN node;
• one RA is handled by only one CN serving node, i.e. one combined MSC+SGSN or one 3G_SGSN, unless "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" is used;
• one LA is handled by only one CN serving node, i.e. one combined MSC + SGSN or one 3G_MSC/VLR, unless "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" is used.

There is no relation between TAs and LA/RAs. However, related configurations may be useful for certain services, e.g. for CS Fallback. The GSM defined relations between LA and RA applies i.e. the following relations between LA and RA are possible:

• RA and LA is equal;
• one RA is a subset of one, and only one, LA, meaning that a RA do not span more than one LA.

The mapping between one LA and RNCs is handled within the MSC/VLR owning this LA. The mapping between one RA and RNCs is handled within the SGSN owning this RA. The mapping between LA and cells respective between RA and cells is handled within RNC.

Operators shall be able to restrict their subscriber's access between E-UTRAN, GERAN and UTRAN radio access, via administrative procedures based on subscription information. In order for the restriction to apply, the network cells shall be organized so that each LA and RA contains either UTRAN or GERAN cells only. TAs apply to E-UTRAN only. Based on the subscription information and the LA/RA/TA information available in the VLR/SGSN/MME, subscriber's access may be rejected during LA/RA/TA update procedure.

The HSS/HLR shall provide the MSC/MSC server/VLR, SGSN and MME with the following information about the subscriber's GERAN and UTRAN access restriction set by the operator determined e.g. by subscription scenario and roaming scenario, as specified in TS 23.008:

• GERAN not allowed.
• UTRAN not allowed.

In addition, the HSS/HLR shall provide SGSN and MME with the following information about the subscriber's E-UTRAN access restriction set by the operator determined e.g. by subscription scenario and roaming scenario, as specified in TS 23.008:

• WB-E-UTRAN not allowed.
• NB-IoT not allowed.

If roaming restriction to specific RATs needs to be enforced by the VPLMN, the SGSN and MME may be configured with a list of HPLMN IDs that are not allowed to access that RAT. The UE shall be notified of the access restriction using the existing procedures for rejection of Location Update, Routing Area Update, Tracking Area Update and Attachment, as defined in TS 24.008 and TS 24.301 and the existing cause values for these procedures.

This concept applies to UTRAN access only. A packet UE (in RRC connected mode) is tracked at the cell level by RNC during an active connection. A packet UE (in RRC connected mode) is tracked at the URA level by RNC when no data are actively transfer, and the probability of data transfer is quite high. A packet UE (in PS-Idle state) is tracked at the RA level by SGSN when no data is actively transferred and the probability of data transfer is quite low. The network operator can optimise paging and updating load by controlling the size of the different areas and the probability of data transfer (controlled by the RRC_connection_release timer). For example, one operator can decide that URA/GRA are small, and that RRC connection are released after a relatively short time of inactivity, so that most attached packet UE are tracked in the RA level (optimum for packet UE mainly using client-server type of service). Another operator can decide that URA/GRA are large, and that RRC connection are released only if RRC connection is lost, so that most attached packet UE are tracked at the URA level. The procedure for the releasing of the RRC connection can be found in TS 23.060 under the Iu release procedure. The URA update procedures can be found in TS 25.331 and GRA update procedures can be found in TS 43.051.