Q931 Message Types

This section outlines the functions of the most important Q.931 messages, and introduces the message acronyms that will be used throughout this chapter. Most message types can be sent from the user to the network, and vice versa.

Set-up Message (SETUP). This is a global message that initiates a call. It is be sent from the calling user to the network, and from the network to the called user. It contains the called number, and other information for the call set-up.

Set-up Acknowledgment Message (SETACK). This is a local message from the network to the calling user. It indicates that more address information is needed to set up the call.

Call Proceeding Message (CALPRC). This is a local message, sent from the network to the calling user, or from the called user to the network. It confirms the receipt of a SETUP message, and indicates that the complete address information for the call has been received, and that the set-up is proceeding.

Progress Message (PROG). This is a local message, sent from the network to the calling user. It contains information about the progress of the call set-up.

Alerting Message (ALERT). This is a global message, sent from the called user to the network, and from the network to the calling user. It indicates that the called party is being informed (alerted) about the arrival of an incoming call.

Connect Message (CONN). This is a global message, sent from a called user to the network, and from the network to a calling user. It indicates that the called user has answered.

Connect Acknowledgment Message (CONACK). This is a local message, acknowledging the receipt of a connect message.

Disconnect Message (DISC). This is a global message, sent from the user to the network, and from the network to the user. It requests the release the connection.

Release Message (RLSE). This is a local message, acknowledging the receipt of a DISC message, and indicating that the sender has cleared the connection at its end.

Release Complete Message (RLCOM). This is a local message, acknowledging the receipt of a RLSE message, and indicating that the sender has released the connection at its end.

Information Message (INFO). This is a global message. It is sent by a calling user who enters called numbers from a keypad at his terminal, and contains one or more digits of the number. An INFO message can also be sent from the network to a calling user. In this case, it orders the user's TE to generate an audible progress tone (busy tone, etc.).

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