SMS-C (operator's server)

The SMS-C (Short Message Service Centre) is the centrepiece of delivery. Every SMS is entrusted to it before reaching its recipient: never do two phones talk to each other directly.

Its operation follows « store and forward »: if the targeted device is switched off or off-network, the message is set aside and delivery attempts repeat for a validity period set by the operator, often 24 to 72 hours. It's this mechanism that guarantees a sent SMS ends up arriving.