6. Message Processing Logic

6.1 Intake paths

CS/PS (legacy 2G/3G)

• UE submits SMS-SUBMIT TPDU over SM-RL/RP (TS 24.011) to MSC (CS) or SGSN (PS).
• The network invokes MAP mo-forwardSM toward the IWMSC/SMSC.
• The SC returns RP-ACK / RP-ERROR and, if requested, later generates SMS-STATUS-REPORT.

LTE over SGs (NAS tunneling)

• UE uses NAS Uplink/Downlink Transport; MME ↔ MSC/VLR via SGsAP.
• From the SC’s perspective, upstream signaling is still MAP; only the last hop is NAS.

IMS (SMSoIP) via IP-SM-GW