Definition
An SMSC (Short Message Service Centre) is the network element that stores, forwards and delivers SMS. It accepts messages from phones or applications and attempts delivery to the recipient’s handset, retrying until the message expires.
3GPP TS 23.040 calls it the Service Centre (SC). It works in store-and-forward mode: if the recipient is unreachable, the SMSC keeps the message and retries according to its schedule until the validity period ends.
To deliver, the SMSC asks the HLR (or HSS/UDM) where the subscriber is, then forwards the message to the serving network over SS7/MAP, Diameter or IMS.
Applications reach an SMSC through SMPP or through a provider’s API. Aggregators run their own SMSC-like platforms that route traffic onward to operator SMSCs.
The SMSC generates delivery receipts and enforces limits such as throughput, sender ID rules and content filtering defined by the operator.