Message Types

The TCAP message type (which is referred to as package type in ANSI) identifies the type of message being sent within the context of a transaction. Table 10-1 lists the seven package types for ANSI and Table 10-2 lists the five message types for ITU.

Table 10-1. Package Types for ANSI

ANSI Package Types	Hex Value	Description
Unidirectional	11100001	Sent in one direction and expects no reply.
Query with Permission	11100010	Initiates a transaction, giving the receiving node permission to end the transaction.
Query without Permission	11100011	Initiates a transaction but does not allow the receiving node to end the transaction
Response	11100100	Ends a transaction.
Conversation with Permission	11100101	Continues a transaction, giving the receiving node permission to end the transaction.
Conversation without Permission	11100110	Continues a transaction, but does not allow the receiving node to end the transaction.
Abort	11110110	Sent to notify the destination node that an established transaction has been terminated without sending any further components that might be expected.

Table 10-2. Message Types for ITU

ITU Message Types	Hex Value	Description
Unidirectional	01100001	Sent in one direction and expects no reply.
Begin	01100010	Initiates a transaction.
(Reserved)	01100011	Not used.
End	01100100	Ends a transaction.
Continue	01100101	Continues an established transaction.
(Reserved)	01100110	Not used.
Abort	01100111	Sent to notify the destination node that an established transaction has been terminated without sending any further components that might be expected.

The message type also infers the stage of transaction processing. Figure 10-4 shows an example of an ITU conversation and an equivalent ANSI conversation. In ITU, a Begin message always starts a transaction, and an End message normally ends the transaction. (The "Transactions" section of this chapter discusses an exception to this rule.) The equivalent ANSI messages that begin and end transactions are Query (with or without permission) and Response, respectively. Conversation (ANSI) and Continue (ITU) messages indicate that further communication is required in an existing transaction.