# Extended data structure substructures overview

Various substructures are referenced in the supplementary service extended data structures. These substructures contain particular types of information, such as address or subaddress information. For a list of the data structures, refer to Supplementary service extended data structures.

Each of these structures contains an invoke field used to indicate the presence or absence of useful data in the structure. If the field is set to ON, the stack uses the information in the structure. Otherwise, the information in the structure is ignored. If the successful invocation of the service requires the inclusion of the parameter and the invoke field is OFF, the service request is rejected.

Some structures contain a reference to a string location and string length. The string location is specified using the offset field in the structure. This offset value is calculated from the address of the structure containing the offset field.

The len field in the structure contains the length of the data. If you null-terminate the field, the length field must not include the null terminator.

Note: Structures sent from the stack do not include null terminations.

If a stack or network error occurs when an attempt is made to invoke or activate a service, the acu_ss_reject substructure is returned in an ACU indication or confirmation message. The fields in this substructure indicate the cause of the rejection.

The following table describes each of the extended data substructures:

Substructure | Description
--- | ---
acu_address | Specifies the full address and subaddress of a party.
acu_call_ret | Specifies a call reference of a party.
acu_conn_id | Specifies the connection information of a party.
acu_party_name | Specifies the name information of a party.
acu_party_num | Specifies the presentation indicator, numbering plan, and screen indicator of a party.
acu_party_subaddress | Specifies the subaddress of a party.
acu_ss_association | Contains a charge ID and charged number, for tracking charging information on transferred or forwarded calls. See AOC and explicit call transfer (ECT) services and AOC and call deflection services.
acu_ss_chan | Specifies the channel information for a party.