The MSC sends the message to the user

[PrisilaED]

The SMS delivery method therefore has a small flaw: messages are initially charged and confirmed to the user when they are sent to the network, not to the final destination, even if the sending client has requested confirmation of delivery. A message may not arrive due to problems with the destination network, expiration of validity or any other reason, but it will still be charged by the operator.

Once a message is ready to be sent at the destination SMSC, originated by a phone number library user or by any other circumstance, it is called MT-SM and the delivery process is as follows:



The SMSC that has received the message stores it in its database and requests the location information from the user's VLR;
If the destination user is available, the SMSC sends the message to the MSC, indicating in which part of the BSS it should be delivered; if it is not available, it is stored in the SMSC for its lifetime.

If the destination user is available, the MSC sends an announcement to the VLR to which the destination user is connected (which may or may not be from its operator) to indicate that a message is going to be delivered.