Error Handling As with any other protocol, errors can occur during TCAP communications. TCAP errors fall into three general categories | Error Handling As with any other protocol errors can occur during TCAP communications. TCAP errors fall into three general categories Protocol Errors Application Errors End-user Errors Protocol Errors Protocol Errors are the result of TCAP messages being incorrectly formed containing illegal values or being received when not expected. For example receiving an unrecognized message type or component type would constitute a protocol error. Another example of an error would be receiving a responding Transaction ID for a nonexistent transaction. While the actual value of the ID might be within the acceptable range of values the lack of a transaction with which to associate the response causes a protocol error. Errors at the Transaction Layer Protocol Errors that occur at the transaction sublayer are reported to the remote node by sending an Abort message type with a P-Abort cause in other words a Protocol Abort. The Abort message is sent only when a transaction must be closed and a Transaction ID can be derived from the message in which the error occurred. Figure 10-13 shows an Abort message being sent for an open transaction in which a protocol error is detected. Figure 10-13. Protocol Error Causes an Abort Because no Transaction ID is associated with a Unidirectional message no Abort message would be sent if the message was received with an error. If a Query or Begin message is received and the Originating Transaction ID cannot be determined because of the message error the message is simply discarded and an Abort message is not returned to the sender. If the Transaction ID can be determined the Abort message is sent to report the error. Without the Transaction ID there is no way for the sending node to handle the error because it cannot make an association with the appropriate transaction. Errors at the Component Layer Protocol errors at the component sublayer are reported using a Reject Component. The errored component s Component ID is reflected in the Reject .
