Section: 2.8.2.2.3 Mapping in the new MME
Content: In order to retrieve the UE's information, e.g. the IMSI, from the old SGSN, the new MME extracts only the RAI and P-TMSI from the GUTI via the reverse mapping procedure to that specified in clause 2.8.2.2.2. This is done in order to be able to include the mapped RAI and P-TMSI, along with the P-TMSI Signature received by the MME from the UE, in the corresponding message sent to the old SGSN (see 3GPP TS 29.060[ General Packet Radio Service (GPRS); GPRS Tunnelling Protocol (GTP) across the Gn and Gp interface ]  [6] and 3GPP TS 29.274[ 3GPP Evolved Packet System (EPS); Evolved General Packet Radio Service (GPRS) Tunnelling Protocol for Control plane (GTPv2-C); Stage 3 ]  [88] for specifics of the messaging). The old SGSN compares the received RAI, P-TMSI and P-TMSI Signature with the stored values for identifying the UE.