Unstructured Supplementary Service Data (USSD) - This is a service as old as mobile telephony itself. This can be accessed through any GSM handset – even good old Nokia 3115. There is no special application or internet access required on mobile handset to access USSD.
A user dials a short code from his/her handset and chooses among various options provided in a set of response menus during a session of up to 3 minutes in case of mKisan.
The progress of one session into the next depends on the user's response. USSD messages in English are 150 alphanumeric characters in length and up to 45 to 60 characters in Unicode (for local language). Local language support depends on type of handset.
Differences between SMS and USSD
||Store and Forward
|Displays directly on phone screen
||Access SMS through phone menu
|Shorter Response Time (60sec)
||Longer Response Time
|Is not stored in the handset - mobile home environment
||Present in the handset, can be stored and forwarded
|Menu driven interface facilitates interactivity
||Interactivity requires user to send a response SMS