SMS messages

An SMS center (SMSC) is responsible for handling the SMS operations of a wireless network. When an SMS message is sent from a mobile phone, it will reach an SMS center first. The SMS center then forwards the SMS message towards the destination.If the recipient is unavailable (for example, when the mobile phone is switched off), the SMSC will store the SMS message. It will forward the SMS message when the recipient is available.It is possible to specify the period after which the SMS message will be deleted from the SMS center so that the SMS message will not be forwarded to the recipient mobile phone when it becomes online. This period is called the validity period.

We must sepecify the address of the wireless network operator's SMSC to use SMS messaging with our mobile phone. Typically an SMSC address is an ordinary phone number in the international format.Normally, the SMSC address is pre-set in the SIM card by the wireless network operator.In Sri lanka for Dialog +9477000003 and for mobitel +9471000003.

If we want to know whether an SMS message has reached the recipient mobile phone successfully or not.We must set a flag in the SMS message to notify the SMS center that we want a status report about the delivery of this SMS message. The status report is sent to us in the form of an SMS message(error or failure e.g. incorrect SMS message format, busy SMS center, etc).

If the mobile phone does not receive the message submission report after a period of time, it concludes that the message submission report has been lost. The mobile phone may then re-send the SMS message to the SMS center. A flag will be set in the new SMS message to inform the SMS center that this SMS message has been sent before. If the previous message submission was successful, the SMS center will ignore the new SMS message but send back a message submission report to the mobile phone. This mechanism prevents the sending of the same SMS message to the recipient multiple times.

After receiving an SMS message, the recipient mobile phone will send back a message delivery report to the SMS center to inform whether there is any error or failure (example causes: unsupported SMS message format, not enough storage space, etc). This process is transparent to the mobile user. If there is no error or failure, the recipient mobile phone sends back a positive delivery report to the SMS center. Otherwise it sends back a negative delivery report to the SMS center.

If the sender requested a status report earlier, the SMS center sends a status report to the sender when it receives the message delivery report from the recipient.If the SMS center does not receive the message delivery report after a period of time, it concludes that the message delivery report has been lost. The SMS center then re-sends the SMS message to the recipient.

Transmission Process of Intra-operator SMS Messages


Transmission Process of Inter-operator SMS Messages

When the originator SMS center receives an inter-operator SMS message, it gets the routing information from the recipient wireless network and delivers the SMS message to the recipient mobile phone directly.This can be used if the two wireless networks involved in the transmission of the inter-operator SMS message are based on similar technologies.


when an SMS message is sent from a GSM network to a CDMA network(if two networks are different).The originator SMS center and the recipient SMS center are interconnected through an SMS gateway or with a communication protocol that is supported by both SMS centers.The recipient SMS center will be responsible for sending the SMS message to the recipient mobile phone and storing the SMS message if the recipient mobile phone is offline.