USSD

Since I started my career as a technical writer for the Business Analyst team, I have been coming across a lot of USSD based work. Thus, I suppose it's only fair of me to write a blog entry on USSD. 

What does the acronym USSD mean? USSD actually stands for Unstructured Supplementary Service Data which is a technology unique to GSM. It is a capability which is built into the GSM standard and is used to support transmitting information over the signaling channels of the GSM network. Frankly, it is used to communicate with the service provider's computers. USSD provides session-based communication which in turn enables a variety of applications. Unlike SMS, USSD provides a real real-time connection in its session, though.  This connection remains open, allowing a two-way exchange of a sequence of data which makes USSD more responsive than services that use SMS

Some of the uses of USSD can be listed as follows:

• WAP browsing, 
• Prepaid callback service(e.g. cheaper phone charges while roaming),
• Location-based content services, 
• Menu-based information services (Stock quotes, Sports results),
• and as part of configuring the phone on the network

Users do not need to access any particular phone menu to enjoy the services with USSD; They can actually enter the USSD command direct from the initial mobile phone screen. This is very fast than SMS as it does not involve the store-and-forward technique of SMS. In addition, it does not involve an SMSC for this operation. 

The USSD commands are routed back to the home mobile network’s Home Location Register (HLR), allowing for the virtual home environment concept. It gives the ability for services (based on USSD) to work just as well and in exactly the same way when users are roaming.

Both SIM Application Toolkit and the Wireless Application Protocol(WAP) support USSD and this technology works on all existing GSM mobile phones

USSD Opearation

USSD is used to send text between the user and some application. USSD acts as a trigger rather than an application itself. However, it enables other applications such as prepaid services. In reality, it is hard to bill for USSD directly. Consequently, the bill is charged for the application associated with the use of USSD such as circuit switch data, SMS, or prepaid.

Format of a USSD message

A typical USSD message starts with an asterisk (*) and is followed by digits that comprise commands or data. Groups of digits may be separated by additional asterisks. The message is terminated with a number sign (#).

Example USSD codes:

• ​*101#​
• ​*109*72348937857623#