D.3 Terminology
23.0403GPPRelease 17Technical realization of the Short Message Service (SMS)TS
An originating SME submits an original SM to an original SC, which delivers the original MT SM to a replying MS. The replying MS sends back a reply MO SM, a MO SM which is generated (automatically or by human operations) in response to the original MT SM, and which is addressed to the originating SME.
If the originating SME is an MS, the original MT SM is submitted within an SMS‑SUBMIT PDU; we say that reply path is requested if the TP‑Reply‑Path parameter is set in the SMS‑SUBMIT PDU of the original MT SM.
We say that reply path exists if the TP‑Reply‑Path parameter was set in the SMS‑DELIVER PDU of the original MT SM; we say that reply path does not exist otherwise.
The replying MS may have a default SC which is normally used for delivering all the MO short messages originated from the replying MS. Alternatively, a human user or automatic application may specify a selected SC for delivering a particular SM (thus the term selected SC refers to an SC address selected for one short message only).