Information elements overview

This section specifies the layout of the information elements (IEs) that comprise the events passed between the application and the SS7 ISUP layer implementation. Each topic in this section contains a description and structure definition for an IE, followed by a table that lists the tokens contained within the respective structure. The tables are formatted using the following standards:

Element header

Each IE contains an element header as the first field in the structure. The element header consists of the presence indicator for the entire IE.

typedef struct elmtHdr   /* element header */
{
    Bool pres            /* present        */
    U8   spare1;         /* for alignment  */
    U16  spare2;         /* for alignment  */
} ElmtHdr;

Extended element

Extended elements enable an application to send IEs that are proprietary or unknown to SS7 ISUP. These extended elements are passed as optional parameters in message types that support optional parameters in them. For example, the IAM message supports optional parameters, so any elements in the extended element fields are encoded into the message.

The RSC (reset circuit) message does not support optional parameters, so no extended elements can be passed in that event structure. Passing extended elements for a message that does not support optional parameters causes the message transmission to fail.

On the receive side of applications, the same event structures with extended elements are returned by ISUPRetrieveMessage. The application can choose to ignore the extended elements.

Note: To transmit or receive extended elements, configure the ISUP task to allow extended elements. For information, see the Dialogic® NaturalAccess™ Signaling Software Configuration Manual.

The extended element consists of the standard element header and an extended token:

typedef struct siElementExt
{
    ElmtHdr eh;      /* element header       */
    TknExt  tknExt;  /* extended information */
} SiElementExt;