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 SMSC Gateway must interoperate with.

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.