Question: What enables intra PLMN roaming and inter access mobility between Gn/Gp 2G and/or 3G SGSNs and an MME/S-GW in the non-roaming scenario?
Option 1: Gn functionality as specified between two Gn/Gp SGSNs, which is provided by the P-GW.
Option 2: Gn functionality as specified between two Gn/Gp SGSNs, which is provided by the MME, and Gn functionality as specified between Gn/Gp SGSN and Gn/Gp GGSN that is provided by the P-GW.
Option 3: Direct Tunnel functionality applied by Rel-7 SGSN.
Option 4: Inter access mobility enabled by E-UTRAN access only.
Explanation: Intra PLMN roaming and inter access mobility between Gn/Gp 2G and/or 3G SGSNs and an MME/S-GW are enabled by two types of Gn functionality: one provided by the MME, which is specified between two Gn/Gp SGSNs, and another provided by the P-GW, which is specified between Gn/Gp SGSN and Gn/Gp GGSN.