Unstructured Supplementary Services Data (USSD) is a means of transmitting information or
instructions over a GSM network. USSD has some similarities with SMS since both use the
GSM network's signalling path (the SDCCH).
Unlike SMS, USSD is not a store and forward service and is session-oriented such that when a
user accesses a USSD service, a session is established and the radio connection stays open
until the user, application, or time out releases it. This has more in common with Data than
SMS. USSD text messages can be up to 182 characters in length.
USSD is defined within the GSM standard in the documents GSM 02.90 (USSD Stage 1) and
GSM 03.90 (USSD Stage 2). In USSD Stage 1, the interactions are initiated by the mobile
phone. In USSD Stage 2, the application can also initiate USSD-based transactions.
• Uses GSM Signalling channels (SDCCH) .
• 182-character messages
• Session-oriented.
• No Store-and-Forward
• Longer character messages than SMS (182 compared to 160)
• Works on all existing GSM terminals
• Supported by SIM Toolkit and WAP
• Stage 2 can provide WAP-like features (on existing handsets)
• Additional loading on signalling channels
• Session-oriented (Traffic loading and costs compared to SMS).
• Stage 1 implementation not intuitive
• Large bills for passing data due to continuous call
connection (CSD)
• Limited size of SMS/USSD messages
• Bearer Services
• Teleservices
• Supplementary Services
• Data Services (CSD, USSD, SMS)
instructions over a GSM network. USSD has some similarities with SMS since both use the
GSM network's signalling path (the SDCCH).
Unlike SMS, USSD is not a store and forward service and is session-oriented such that when a
user accesses a USSD service, a session is established and the radio connection stays open
until the user, application, or time out releases it. This has more in common with Data than
SMS. USSD text messages can be up to 182 characters in length.
USSD is defined within the GSM standard in the documents GSM 02.90 (USSD Stage 1) and
GSM 03.90 (USSD Stage 2). In USSD Stage 1, the interactions are initiated by the mobile
phone. In USSD Stage 2, the application can also initiate USSD-based transactions.
Unstructured Supplementtarryy Serrviiccee Datta ((USSD))
• Text-based messaging Service• Uses GSM Signalling channels (SDCCH) .
• 182-character messages
• Session-oriented.
• No Store-and-Forward
Comparriison off USSD and SMS
• USSD Advantages:
• Up to seven times faster than SMS• Longer character messages than SMS (182 compared to 160)
• Works on all existing GSM terminals
• Supported by SIM Toolkit and WAP
• Stage 2 can provide WAP-like features (on existing handsets)
• USSD Disadvantages:
• No Store-and-Forward.• Additional loading on signalling channels
• Session-oriented (Traffic loading and costs compared to SMS).
• Stage 1 implementation not intuitive
Inadequacies Of Current Data Services
• Slow data rates 9.6Kbps• Large bills for passing data due to continuous call
connection (CSD)
• Limited size of SMS/USSD messages
Summary
This section has covered the following topics:• Bearer Services
• Teleservices
• Supplementary Services
• Data Services (CSD, USSD, SMS)