The path of a MO-SM
When a network user generates a short message (MO-SM) the following events occur:
The HLR where the user is registered decides whether or not he can phone number library send messages; if everything is in order,
The MSC to which the user is connected receives the message, sends the necessary information to the VLR for subsequent charging and then forwards it to the originating SMSC;
The source SMSC sends the message to the destination SMSC (labeled SME in the figure). Once there, it is converted to MT-SM and processed as we will see below.
The destination SMSC reports the status of the message and returns a reception report to the MSC and the user. The user screen displays “message sent”.
If the user has requested it, they will subsequently receive a status message confirming whether the target user has received the message or not, and an error message if it expires.
