ITU Protocol Message Contents

The definition of each message type indicates a set of fields that comprise the message. While some fields are mandatory, others are optional. As specified by Q.773, the standard set of ITU messages includes:

• Unidirectional

• Begin

• End

• Continue

• Abort

The following sections describe these messages, the fields that are included in each one, and indicate which fields are mandatory or optional.

Unidirectional Message

The Unidirectional Message is sent when no reply is expected. Table 10-9 lists the message contents.

Table 10-9. Unidirectional Message Fields

Unidirectional Message Fields	Mandatory/Optional
Message Type Total Message Length	Mandatory
Dialogue Portion	Optional
Component Portion Tag Component Portion Length	Mandatory
One or More Componnts	Mandatory

Begin Message

The Begin Message is sent to initiate a transaction. Table 10-10 lists the message contents.

Table 10-10. Begin Message Fields

Begin Message Fields	Mandatory/Optional
Message Type Total Message Length	Mandatory
Originating Transaction ID Tag Transaction ID Length Transaction ID	Mandatory
Dialogue Portion	Optional
Component Portion Tag Component Portion Length	Optional[*]
One or More Components	Optional

^[*] The component Portion Tag is present only if the message contains components.

EndMessage

The End Message is sent to end a transaction. Table 10-11 lists the message contents.

Table 10-11. End Message Fields

End Message Fields	Mandatory/Optional
Message Type Total Message Length	Mandatory
Destination Transaction ID Tag Transaction ID Length Transaction ID	Mandator
Dialogue Portion	Optional
Component Portion Tag Component Portion Length	Optional[*]
One or More Components	Optional

^[*] The component Portion Tag is present only the message contains components.

Continue Message

The Continue Message is sent when a transaction has previously been established and additional information needs to be sent without ending the transaction. Table 10-12 lists the message contents.

Table 10-12. Continue Message Fields

Continue Message Fields	Mandatory/Optional
Message Type Total Message Length	Mandatory
Originating Transaction ID Tag Transaction ID Length Transaction ID	Mandatory
Destination Transaction ID Tag Transaction ID Length Transaction ID	Mandatory
Dialogue Portion	Optional
Component Portion Tag Component Portion Length	Optional[*]
One or More Components	Optional

^[*] The component Portion Tag is present only if the message contains components.

Abort Message

The Abort Message is sent to terminate a previously established transaction. Table 10-13 lists the message contents.

Table 10-13. Abort Message Fields

Abort Message Fields	Mandatory/Optional
Message Type Total Message Length	Mandatory
Destination Transaction ID Tag Transaction ID Length Transaction ID	Mandatory
P-Abort Cause Tag P-Abort Cause Length P-Abort Cause	Optional[*]
Dialogue Portion	Optional

^[*] P-Abort is present when the TC-User generates the Abort message.