Mapping between Temporary and Area Identities for EUTRAN- and UTRAN/GERAN-Based Systems

For the construction of the RA update request message in GERAN/UTRAN or TA update request message in E-UTRAN the following identities should be included.

In GERAN and UTRAN the RAI is constructed from the MCC, MNC, LAC, and RAC. In addition, the routing area update request message contains the P-TMSI that includes the mapped Network Resource Identifier (NRI) that is used in Iu flex networks. (An example of NRI usage is given in Kreher and Ruedebusch, 2007.)

P-TMSI should be of 32-bit length where the two topmost bits are reserved and always set to 11. These are needed since the GERAN representation of P-TMSI, of the form TLLI (Temporary Logical Link Identity), imposes this restriction. Hence, for a UE which may hand over to GERAN/UTRAN (based on subscription and UE capabilities), the corresponding bits in the M-TMSI are set to 11.

The NRI field is of variable length and should be mapped into the P-TMSI starting at bit 23 and down to bit 14. The most significant bit of the NRI is located at bit 23 of the P-TMSI regardless of the configured length of the NRI.

In the case of a combined MME-SGSN node, the NRI of the SGSN part and the MMEC of the MME part refer to the same combined node. The RAN configuration allows NAS messages on GERAN/UTRAN and E-UTRAN to be routed to the same combined node. The same or different values of NRI and MMEC may be used for a combined node.

The mapping of the GUTI should be done to a combination of the RAI of GERAN/UTRAN and the P-TMSI as follows:

E-UTRAN <MCC>	maps to GERAN/UTRAN <MCC>
E-UTRAN <MNC>	maps to GERAN/UTRAN <MNC>
E-UTRAN <MME Group ID>	maps to GERAN/UTRAN <LAC>
E-UTRAN <MME Code>	maps to GERAN/UTRAN <RAC>

It is also copied into the eight most significant bits of the NRI field within the P-TMSI. E-UTRAN <S-TMSI> maps as follows:

• 22 bits of the E-UTRAN <M-TMSI> starting at bit 30 and down to bit 9 are mapped into the remaining 22 bits of the GERAN/UTRAN <P-TMSI>;
• the remaining 8 bits of the E-UTRAN <M-TMSI> are copied into 8 bits of the <P-TMSI signature> field.

For the UTRAN, the 10-bit-long NRI bits are masked out from the P-TMSI and also supplied to the RAN node as an Intra-Domain NAS Node Selector (IDNNS).

The mapping of P-TMSI (TLLI) and RAI in GERAN/UTRAN to GUTI in E-UTRAN should be performed as follows:

GERAN/UTRAN <MCC>	maps to E-UTRAN <MCC>
GERAN/UTRAN <MNC>	maps to E-UTRAN <MNC>
GERAN/UTRAN <LAC>	maps to E-UTRAN <MME Group ID>
GERAN/UTRAN <RAC>	maps to 8 bits of the M-TMSI

The eight most significant bits of GERAN/UTRAN <NRI> map to the MMEC.

GERAN/UTRAN <P-TMSI or TLLI> excluding the eight most significant bits at the NRI position maps to the remaining bits of the M-TMSI.

The values of <LAC> and <MME group id> should be disjoint, so that they can be differentiated. It is recommended that the most significant bit of the <LAC> be set to zero, and the most significant bit of <MME group id> set to one.