General Process
- SMS Application or Cellular Telephone
Whether an SMS message originates from a phone or an application, the process is the essentially the same. If the message is coming from a cell phone it first is sent to the cell tower and then the message is forwarded on to the cell carrier's Short Message Service Center (SMSC).
- SMSC
The SMSC that receives an SMS message attempts to send the message to the recipient. The technology works as "store and forward", meaning that the SMSC will store the message until it can be delivered. This enables the message to be saved and sent later in case the recipient's phone is not turned on or is out of range.
Incoming Messages - Also known as Mobile Originated (MO)
- User/cell subscriber sends a message to an application-enabled short or long code
An application first needs to be setup on a short code or a long code that can accept SMS data. Short codes are simply short numbers, 4 or 5 digits long. Short codes are issued by the CSCA and are leased to appicants on a quarterly basis. Long codes are simple 10-digit telephone numbers that can receive SMS data, and are typically provisioned by an SMS aggregator such as Andexus, LLC.
- Application Processes Message
The application setup on the number can do any number of things. Typically the application will process the body of the text message and return some value or set of values. The application can also process additional metadata, such as the user's location or phone number. This message transaction has a unique identifier, so an application can process incoming messages as a conversation, progressing its responses based on multiple user inputs or "stages".
- Application Returns Message
After processing the message the application sends a reply with whatever content the appication is designed to serve.
Outgoing Messages - Also known as Mobile Terminated (MT)
- Application Initiates Message
An application initiates a message. The "trigger" or "event" can be any number of things. Perhaps it is as simple as a user pressing a button on a website. While this is a very common event to initiate an outgoing SMS message, the events can be more complex such as a user pressing a key on their phone, an order being processed, or even a scheduled event reaching its designated date/time.
- User receives message
The message is most typically static in nature, meaning that is only contains information. However, because an application can keep track of SMS unique identifiers, an application can "converse" with a recipient. Any replies to a message can trigger processing and responses from the application.
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