# Sending additional information elements

Applications can add Q.931 information elements, including user-to-user information, to some ISDN messages.

The array, ie_list in the extended parameter structure, can be filled with fully formed Q.931 information elements to be passed transparently through the stack. This list must be terminated with a null (0x00) byte.

For example, to send user-to-user information elements using the ie_list array:

ie_list[0] = 0x7E; /* user-to-user ie codepoint */
ie_list[1] = 0x03; /* length of user-to-user ie */
ie_list[2] = 0x04; /* user-to-user data = IA5 */
ie_list[3] = 'A'
ie_list[4] = 'B'
ie_list[5] = 0x00; /* end of additional information elements */
/* note that this is not the string terminator */
/* for the user-to-user IA5 data. */