An application using the connectionless service sends data to the far end by invoking SCCPUDataRqst. Depending on the size of the data and the class of service employed, the SCCP task generates a unitdata (UDT) or extended unitdata (XUDT) message to the far end as shown in the following illustration. There is no response from the far end to these messages.
If the far end SCCP layer cannot process the received data message and returns a unitdata service message (UDTS) or extended unitdata service message (XUDTS) to the SCCP task, the application is notified with a SCCPStatusIndication.
Incoming unitdata (UDT and/or XUDT) messages are presented to the application with a SCCPUDATIND event.
If the application has selected the return on error option on a unitdata request and either the local SCCP layer is unable to deliver the message or the remote SCCP returns the message as undeliverable (through the UDTS or XUDTS message), the application is notified with a SCCPSTAIND event. This event contains the reason for the delivery failure and the original content of the undeliverable message.