Components Components are a means of invoking an operation at a remote node. A TCAP message can contain several components, thereby invoking several operations simultaneously. | Components Components are a means of invoking an operation at a remote node. A TCAP message can contain several components thereby invoking several operations simultaneously. The TCAP component is based on the ITU specification for Remote Operations in Message Handling Systems. ITU has replaced this specification. The specification defines the following four Operational Protocol Data Units OPDUs Invoke Requests an operation to be performed Return Result Reports the successful completion of a requested operation Return Error Reports the unsuccessful completion of a requested operation Reject Reports a protocol violation such as an incorrect or badly-formed OPDU Each of the TCAP component types directly correlates to one of the previous OPDU types. The Invoke and Return Result component types are used for carrying out the normal operations between TCAP users. The Return Error and Reject component types are used for handling error conditions. The contents of the Invoke and Return Result components include the following information Component Type Component ID Operation Code Invoke Component only Parameters The contents of the Return Error and Reject components are similar to the Invoke and Return Result components except that the Operation Code used in an Invoke component is replaced by an Error Problem code. The following sections discuss the contents of the components listed previously. The Error Handling section later in this chapter addresses the Return Error and Reject components. Invoke and Return Result Components Under normal circumstances Invoke and Return Result Components are sent to carry out and verify operations between two communicating entities. For example an SSP might invoke a number translation at an SCP resulting in a new number being returned. A number of services such as Toll-free Premium Rate and Local Number Portability use TCAP to look up numbers in this manner. The application layer for these services and others use a standardized
