How SMS works ?

I think everyone in whole world know about SMS, they use it to tell something about their works, relationship etc to others. Every mobile operator in the world should have SMS services beside the voice. With voice they can real time communication in same time, but in SMS we just send our message and wait whether it delivered or not. Some question often arises is how SMS works ? why my message not delivered to my friend ? why sometimes the message just arrived to my friends in the next hour not real time ?
Here I just try to explain the basic SMS flow and works in our mobile operator to make understand us as a mobile subscriber.

SMS or Short Message Service is a service provided by an operator of GSM / CDMA besides Voice service. SMS and Voice is primary service in common mobile operator. The SMS is non-circuit related, while the circuit voice service is so important to understand in terms of the protocol used. It is better to know the basic protocol used in SMS, that is SS7. I will explain it overview in other articles.

Basicly we can send SMS to other subscriber or to some services like short code which have digit less than prefix number. They works in different environment protocol they are using. The common protocols you have understand SMS are SS7 (Signalling System No 7 ) and SMPP (Short Message Peer to Peer Protocol). Those protocols representative two different domains : SS7 used to support communication between elements core network in mobile operator, while the SMPP used for communication in IP domain between SMSC ( SMS Center) and its external services like ESME ( External Shortcode Messaging Entity ) such as Service Provider or Content Provider.

Maybe you ever got message from a shortcode which consists of advertisement from your operator. It is one of services which operator can provide. It is using SMS blast server which do interconnection with SMS Center through the SMS Gateway. So, SMS Center using SMPP protocol to communicate with SMS Gateway before sending SMS to ESME.
How about Service Provider which using like web application in their service? Who it can communicate with SMS gateway and SMSC instead of they are using SMPP Protocol. Here SMS Gateway should have ability to do conversion from SMPP Protocol to HTTP protocol which a Service Provider used. In this article, I just explain the basic overview about SMS.

The items you should know besides the protocols and SMS Center are about elements of core network and their function like HLR, MSC. IN, BSC or BTS. In the next articles I will explain about basic mechanism of SMS. I hope with this articles you have basic overview before we discuss further as technically procedure of SMS works.