2. SMS Fundamentals

This chapter introduces the Short Message Service (SMS) across legacy (GSM/UMTS), LTE, IMS interworking, and 5G. It focuses on the roles and procedures your SMSC Gateway must interoperate with, and uses only material standardized by 3GPP and IETF.

2.1 What is an SMSC

Service Centre (SC / SMSC). The Service Centre is the function responsible for relaying and store‑and‑forwarding short messages between an SME (application, MS) and a mobile station. The SC is logically outside the PLMN but may be integrated with operator nodes. Its core responsibilities include accepting MO submissions, retaining responsibility for delivery until a report or validity expiry, and delivering MT messages to recipients via the mobile network.