Details about the Unstructured Supplementary Service Data
USSD full form is Unstructured Supplementary Service Data. USSD provides a simple interface to communicate with the mobile phone in binary mode by encoding messages of up to 240 (80 hexadecimal) bytes each. It was first introduced by the GSM Association in November 1988 and it is used mostly for text-based services such as bank transfers, flight booking, weather information and horoscopes. USSD can be accessed through the GSM access application which resides on the SIM card or UICC card of a device. GSM service providers have set up these numbers for specific purposes, such as programme updates, debugging services and checking airtime balances.
How does it work?
USSD uses SMS as a transport channel. The USSD service is activated by dialling a specific number. The service provider also has the ability to activate the Unstructured Supplementary Service Data services by sending an SMS to the SIM card or UICC. The SIM card or UICC must be active and ready for sending messages. If the SIM card is in use and not available for receiving messages, a 0 needs to be encoded with those initial characters in order for it to be accepted. It is mostly used for text-based services such as bank transfers, flight booking, weather information and horoscopes.
About the design:
USSD full form is Unstructured Supplementary Service Data. The A5/1 and A5/3 systems are designed to support the following features with respect to embedded devices: A5/1 and A5/3 are considered as limited service systems, as they have a greater restriction on memory size than normal GSM systems. This limits how many software services or applications can be run simultaneously, which makes the system unsuitable for most environments. It also limits communication bandwidth throughput by a factor of 2. This means that some types of services cannot be provided efficiently – especially those which require frequent small message exchanges.