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Unstructured Supplementary Service Data

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USSD on a Sony Ericsson mobile phone

Unstructured Supplementary Service Data (USSD) is a protocol used by GSM cellular telephones to communicate with the service provider's computers. USSD can be used for WAP browsing, prepaid callback service, mobile-money services, location-based content services, menu-based information services, and as part of configuring the phone on the network.[1]

USSD messages are up to 182 alphanumeric characters in length. Unlike Short Message Service (SMS) messages, USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. This makes USSD more responsive than services that use SMS.[1]

Uses

The user composes a message—usually rather cryptic—on the phone keyboard. The phone sends it to the phone company network, where it is received by a computer dedicated to USSD. The answer from this computer is sent back to the phone. The answer could be seen on the phone screen, but it is usually with a very basic presentation. The messages sent over USSD are not defined by any standardization body, so each network operator can implement whatever it finds suitable for its customers.

USSD can be used to provide independent calling services such as a callback service (e.g. cheaper phone charges while roaming) or interactive data service (e.g. stock quotes, sports results).

USSD is commonly used by pre-paid GSM cellular phones to query the available balance. The vendor's "check balance" application hides the details of the USSD protocol from the user.

Some payment methods, such as SharEpay, SWAP Mobile in South Africa, Mobipay in Spain, M-Pesa in Tanzania (but not in Kenya, where M-Pesa menus are provided by STK rather than USSD), and mPay in Poland use USSD.

Some operators use USSD to provide access to real-time updates from social-networking websites like Facebook and Twitter.[2]

Technical details

All GSM phones have USSD capability. It is generally associated with real-time or instant messaging services. There is no store-and-forward capability, as is typical of other short-message protocols like SMS—in other words, an SMSC is not present in the processing path.

USSD Phase 1, specified in GSM 02.90, only supports mobile-initiated ("pull") operation. In the core network, the message is delivered over MAP. USSD Phase 2, specified in GSM 03.90, supports network-initiated ("push") operation as well.

Format

A typical USSD message starts with an asterisk (*) 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 (#).[1]

Example USSD codes:

  • *101#
  • *109*72348937857623#

After entering a USSD code on your GSM handset, the reply from the GSM operator is displayed within a few seconds.

See also

References

  1. ^ a b c "Unstructured Supplementary Services Data (USSD)". TelecomSpace. Retrieved August 23, 2010.
  2. ^ Shetty, Anuradha (July 16, 2011). "TATA Docomo Introduces Facebook, Twitter Access via USSD". Network 18 India. Retrieved July 18, 2011. {{cite web}}: Unknown parameter |site= ignored (help)


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