SMSC :-
The Short Message Service Centre (SMSC) is an element in a GSM Network responsible for the delivery of short messages (SMS). All messages are sent to the SMSC. The SMSC stores the messages, extracts the destination from it and tries to deliver the message. If the message cannot be delivered, the SMSC will try again to deliver the message in a so-called retry-schedule. If the mobile phone is turned on or comes within reach of the network, the SMSC will also retry to deliver the message. If a mobile telephone received a message, it will send an acknowledgement back. Usually the message will be discarded after two days if the destination cannot be reached. Typically it is SMS-SC i.e. Short Massage Centre-Service Center. The number of the SMSC has to be programmed in the mobile phone.
Basically SMSC Trajectories of SMS are; Mobile to Mobile known as MO-MT (Mobile Originated-Mobile Terminated), Mobile to a content provider (also called as Large Account / ESME) referred as MO-AT (Mobile Originated - Application Terminated) and Application to a Mobile, referred as AO-MT (Application Originated - Mobile Terminated). The task of SMSC is Reception, Storage, Forwarding and Delivery of text messages (SMS) to wireless network users and Maintenance of unique time stamps in text messages.
When a user sends a text message (SMS message) to another user, the message gets stored in the SMSC (short message service center) which delivers it to the destination user when they are available. This is a store and forward option. Undelivered massages are deleted after pre-defined time duration.