One difference is that for SMS, it uses “store and forward” technique in delivering text messages. A text message can first be sent to the sender’s Short Message Service Center (SMSC) before the SMSC trying to deliver the text to the recipient. The sender received an indication as to whether the text has successfully received the SMSC (Dialogic, 2017). However, the text is not necessarily a guarantee that it will reach the recipient instantly. The concept of the SMS router can be used in improving SMS delivery time in many instances. For USSD, information gets sent directly from the sender’s mobile handset in an application platform being used in handling the USSD service. There are many examples of mobile services or apps that use USSD in Africa. Some of these apps include the following:
Push USSD Notifications for OTP (one-time pins)
Push USSD notifications for OTP is the app used when the mobile user initiates the “Balance Enquiry and Top Up” service, through dialing the USSD string defined by the provider, such as *#123#. The application receives the service request from the mobile user and responds by sending the user a menu of options. The user can then respond by selecting an option such as “Current balance” (Dialogic, 2017). The application then sends back details on the mobile user’s current account balance as well as giving an option of topping up the balance. The user then selects to top up their account, and the USSD app sends an updated balance and ends the session.
Ushahidi is yet another USSD application in Africa, which allows submission via USSD menu. The app also uses Google Maps’ API for geolocation that is based on raw address input. Ushahidi uses existing architecture from GSM networks, same as many other USSD applications.
Different banks also have their mobile USSD applications in Africa. The USSD application allows the mobile banking service to send an SMS message to a mobile subscriber (Dialogic, 2017). The client approves a wire transfer transaction. Before the user responds, another message is sent from the banking service to ask the user if they would like to see their new checking account balance. There is no way the user can respond unambiguously to either the questions. Also, SMS does not necessarily guarantee the delivery, nor does it guarantee the order in delivery.
USSD Instant Messaging
Initially, USSD was designed to resolve the issues with SMS, in situations where SMS was considered unreliable and stateless. USSD instant messaging is available on any 2G or later mobile handsets, which is a plus for virtually any mobile phone user in Africa, just as they support SMS.
The USSD application is used in showing how Restcomm interconnects with mobile networks in providing intuitive Web APIs for Restcomm application developers. The form includes vital USSD configuration settings such as the Voice URL used in handling voice calls through application logic, USSD URL for USSD app logic, SMS URL for SMS interactions.