Unstructured Supplementary Service Data (USSD)

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The DoT said that it has come to its notice that USSD based call forwarding facility, most commonly known *401# services for unconditional call forwarding services, is being misused for some unwarranted activities.

About Unstructured Supplementary Service Data (USSD)

It is a communications protocol used in Global System for Mobile Communications (GSM) networks for sending short text messages.
It is an instant messaging service and messages are not stored on the operator side or on the subscriber’s device.
USSD format: It generally exist as one of two types, depending on their origin:
- A USSD Pull is an outgoing request from the user in the form of an MMI command.
- A USSD Push is a message from the operator that is displayed on the user’s screen.
- The user can send the operator a request in the form of a USSD command. Commands consist of the * and # characters and numeric codes.
- The chain begins with * or # (which can occur more than once, separating commands from subcommands) and usually ends with #.
- The maximum length of a USSD message is 182 characters, but in practice even the longest requests rarely exceed 20.
It is usedto display balance deduction in mobile phones where a message pops-up on the device screen after a call or outgoing SMS.It is also used for checking IMEI numbers of mobiles.

Q1) What is the International Mobile Equipment Identity (IMEI) number?

The International Mobile Equipment Identity or IMEI is a unique number that is used to identify a device on a mobile network. It has 15 digits, and is like your phone’s unique identity.

Source: DoT asks telcos to suspend USSD-based call forwarding, switch to alternate mode from Apr 15