Photo courtesy of Yahoo Mobile

If you are here reading this post then you're probably very old or very bored. Everyone (and I mean everyone) under the age of 40 probably knows what a SMS is and use it on a daily basis. If you are old it's more than ok with us - we respect the golden age people. If you are very bored, we hope you are enjoying yourself – that's why we are here.

SMS is short for "Short Message service" and it is available in most of the cell phones sold in the markets worldwide. The service allows users to send and receive very short text message (from 150 to 160 Characters) through their network operator system. Other sending opportunities include via internet web sites usually operated by the major cellular providers.

Once a message is sent, it is received by a Short Message Service Center (SMSC), which must then see to it that it gets to the appropriate mobile device. To do this, the SMSC sends a SMS Request to the home location register (HLR) to find the roaming user. Once the HLR receives the request, it will respond to the SMSC with the subscriber's status: 1) inactive or active 2) where subscriber is roaming.

If the response is "inactive", then the SMSC will hold onto the message for a certain amount of time. When the subscriber accesses his device, the HLR sends a SMS Notification to the SMSC which will then attempt delivery. The SMSC transfers the message in a Short Message Delivery Point to Point format to the serving system. The system pages the mobile device, and if it responds, the message then gets delivered. Once the SMSC receives verification that the message was received by the end user, it then categorizes the message as "sent" and will not attempt to send it again. Fascinating.