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MB USSD Operations

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This topic describes the operations to send and receive messages using the Unstructured Supplementary Service Data (USSD) capabilities of an MB device.

USSD support is optional and when supported is only available on GSM networks. Miniport drivers that support USSD must set the WWAN_CTRL_CAPS_USSD capability flag as part of the WwanControlCaps member of the WWAN_DEVICE_CAPS structure when processing OID_WWAN_DEVICE_CAPS requests. If miniport drivers do not support USSD, they must not set this flag and should return WWAN_STATUS_NO_DEVICE_SUPPORT for all USSD-related OIDs.

The MB driver model supports the following USSD operations: Device initiated operations:

  • Sending a USSD message on a newly created USSD session

  • Sending a USSD message on a newly created USSD session

  • Sending a USSD message on an existing USSD session

  • Terminating the USSD session

For more information on device initiated operations, see OID_WWAN_USSD.

Network initiated operations:

  • Receiving a USSD message on a newly created USSD session

  • Receiving a USSD message on an existing USSD session

  • Termination the USSD session

For more information on network initiated operations, see NDIS_STATUS_WWAN_USSD.

The USSD protocol only allows a single USSD session at any time. For device initiated operations, the RequestType member of the WWAN_USSD_REQUEST structure indicates the purpose of the request OID:

  • WwanUssdRequestInitiate is used to create a new USSD session and send the provided USSD string to the network. If a USSD session already exists, the driver must fail the request with an event of type WwanUssdEventOtherLocalClient. A USSD string must be present. For example, the length must be between 1 and 160 bytes.

  • WwanUssdRequestContinue is used to send a USSD string on an existing session. A USSD string must be present. For example, the length must be between 1 and 160 bytes.

  • WwanUssdRequestCancel is used to terminate the existing session. The driver must respond with an event of type WwanUssdEventTerminated, even if no session existed (which may happen during a concurrent release of the session from the network and the local client). The content of the USSD string must be ignored for this request; the string length is set to zero to indicate that there is no USSD string.

For network initiated operations, the EventType member of the WWAN_USSD_EVENT structure indicates the high level purpose of the indication:

  • The event WwanUssdEventNoActionRequired is used for network initiated USSD notifications, or when no further information is needed after a mobile initiated operation. The event WwanUssdEventActionRequired is used for network initiated USSD requests, or when further information is needed after a mobile initiated operation. Both events require a non-empty USSD string to be present. The SessionState member is used to indicate if the USSD string is the first message of a USSD session; it must be set to WwanUssdSessionStateNew for the first message of a network initiated USSD session and to WwanUssdSessionStateExisting in all other cases.

  • The event WwanUssdEventActionRequired also indicates that the session is still open. All other events indicate that the session has been closed.

  • The events WwanUssdEventNoActionRequired and WwanUssdEventActionRequired are the only events that contain a USSD string. All other events must set the USSD string length to 0 to indicate that the string is absent. The value of the SessionState member is ignored if no string is present.

  • The event WwanUssdEventTerminated is used to indicate that the USSD session has been terminated.

  • The event WwanUssdEventOtherLocalClient is used to indicate that a new USSD session cannot be established because there is already a session opened. This includes sessions that are invisible to the MB stack such as a USSD session termination in the SIM.

  • The event WwanUssdEventOperationNotSupported is used to indicate that the previous request is not supported by the driver or device.

  • The event WwanUssdEventNetworkTimeOut is used to indicate that the session was closed due to a session timeout either by the network or locally. The driver or device is responsible for timing out an inactive USSD session after an implementation specific timeout.