Appendix B. ISUP Messages (ANSI/UK/ETSI/ITU-T) The table in this appendix summarizes ISDN User Part (ISUP) messages and the p urpose of each. For an introduction to ISUP, refer to Chapter 8, "ISDN User Part (ISUP)." Table B-1. ISUP Messages Message/Code Full Message Name Purpose ACM 0 0 0 0 0 1 1 0 Address Complete Sent in the backward direction, indicating that all address signals have been received and that the call set-up is progressing. ANM 0 0 0 0 1 0 0 1 Answer Sent in the backward direction to indicate that the called party has answered the call. May be used to trigger billing and measurements of call duration. APM (NI99)(I) 0 1 0 0 0 0 0 1 Application Transport Sent in either direction to convey application information using the Application Transport Mechanism. BLO 0 0 0 1 0 0 1 1 Blocking Sent to the exchange at the far end to block call originations for the specified circuit. BLA 0 0 0 1 0 1 0 1 Blocking Acknowledgement Sent in response to a BLO message, indicating that the identified circuit has been blocked to outgoing traffic. CPG 0 0 1 0 1 1 0 0 Call Progress Sent in either direction, indicating that an event has occurred in the progress of a call. CGB 0 0 0 1 1 0 0 0 Circuit Group Blocking Sent to the exchange at the far end to block call originations for a specified group of contiguous circuits. CGBA 0 0 0 1 1 0 1 0 Circuit Group Blocking Acknowledgement Sent in response to a CGB, indicating that the identified group of circuits has been blocked to outgoing traffic. CQM (N) (NS67) 0 0 1 0 1 0 1 0 Circuit Group Query [Circuit Query Message (ANSI)] Sent on a routine or demand basis to request the exchange at the other end of a group of circuits for the state of the circuits within the specified range. CQR (N) (NS67) 0 0 1 0 1 0 1 1 Circuit Group Query Response [Circuit Query Response Message (ANSI)] Sent in response to a CQM, indicating the state of the previously identified group of circuits. GRS 0 0 0 1 0 1 1 1 Circuit Group Reset Sent to align the state of a group of circuits with the state of those circuits as perceived by the exchange after releasing any calls in progress, and after removing any blocked condition from that group of circuits. Message is sent when an exchange does not know the particular state of a group of circuits, because of memory problems, for example. GRA 0 0 1 0 1 0 0 1 Circuit Group Reset Acknowledgement Sent in response to a GRS message to indicate that the group of circuits has been realigned. CGU 0 0 0 1 1 0 0 1 Circuit Group Unblocking Sent to the exchange at the far end to remove the blocked condition for a specified group of circuits, allowing call originations to occur. CGUA 0 0 0 1 1 0 1 1 Circuit Group Unblocking Acknowledgement Sent in response to a CGU, indicating that the identified group of circuits is now unblocked. CRM (A) 1 1 1 0 1 0 1 0 Circuit Reservation Message Sent in the forward direction only when interworking with exchange access multi-frequency signaling to reserve a circuit and initiate any required continuity checks. CRA (A) 1 1 1 0 1 0 0 1 Circuit Reservation Acknowledgement Sent in the backward direction in response to a CRM, indicating that the circuit has been reserved for an outgoing call. CVR (A) 1 1 1 0 1 0 1 1 Circuit Validation Response Sent in response to a CVT to convey translation information for the indicated circuit. CVT (A) 1 1 1 0 1 1 0 0 Circuit Validation Test Sent on a routine or demand basis to request translation information for the identified circuit. CRG (N) (I) (NS67) 0 0 1 1 0 0 0 1 Charge Information Information sent in either direction for accounting and/or call-charging purposes. CFN (NS67) 0 0 1 0 1 1 1 1 Confusion Sent in response to any message (other than a confusion message) to indicate that all or part of a received message was unrecognized. CON (I) 0 0 0 0 0 1 1 1 Connect Sent in the backward direction, indicating that all of the address signals required for routing the call to the called party have been received, and that the call has been answered. COT (NUK) 0 0 0 0 0 1 0 1 Continuity Sent in the forward direction to indicate the result of the completed continuity test. CCR (NUK) 0 0 0 1 0 0 0 1 Continuity Check Request Sent to request a continuity check on the identified circuit (requests the exchange at the circuit to attach continuity checking equipment). EXM (A) 1 1 1 0 1 1 0 1 Exit Message Sent in the backward direction from an outgoing gateway exchange to indicate that the call has successfully progressed to the adjacent network (Intranetwork use only). FAC (NS67) 0 0 1 1 0 0 1 1 Facility Sent in either direction at any phase of a call to request an action at another exchange. Also used to carry the results, error, or rejection of a previously requested action. FAA (I) (NS67) 0 0 1 0 0 0 0 0 Facility Accepted Sent in response to a facility request message, indicating that the requested facility has been invoked. FAJ (I) (NS67) 0 0 1 0 0 0 0 1 Facility Reject Sent in response to a facility request message (FAR) to indicate that the facility request has been rejected. FAR (I) (NS67) 0 0 0 1 1 1 1 1 Facility Request Sent from one exchange to another to request activation of a facility. FOT (NUK) 0 0 0 0 1 0 0 0 Forward Transfer Sent in the forward direction on semi- automatic calls when the operator wants an operator at a distant exchange to help. IDR (I) (NS67) 0 0 1 1 0 1 1 0 Identification Request Sent in the backward direction to request an action regarding the malicious call identification supplementary service. IDS (I) (NS67) 0 0 1 1 0 1 1 1 Identification Response Sent in response to the IDR message. INF (N) (NS67) 0 0 0 0 0 1 0 0 Information Sent to convey additional call-related information that may have been requested in the INR message. INR (N) (NS67) 0 0 0 0 0 0 1 1 Information Request Sent by an exchange to request additional call-related information. IAM 0 0 0 0 0 0 0 1 Initial Address Sent in the forward direction to initiate seizure of an outgoing circuit and to transmit number and other information related to the routing and the handling of a call. LPA (N) (NS67) 0 0 1 0 0 1 0 0 Loop Back Acknowledgement Sent as a response to a CCR to indicate that the requested loop back has been connected (or transceiver in the case of a 2-wire connection). LOP (I) (NI97) 0 1 0 0 0 0 0 0 Loop Prevention Sent to convey information required by the ECT (explicit call transfer) supplementary service. NRM (I) (NS67) (NUK) 0 0 1 1 0 0 1 0 Network Resource Management Sent in order to modify network resources associated with a certain call, and sent along an established path in any direction in any phase of the call. OLM (N) (I) (NS67) 0 0 1 1 0 0 0 0 Overload Sent in the backward direction on non- priority calls in response to an initial address message (IAM) to invoke temporary trunk blocking of the concerned circuit when the exchange generating the message is subject to load control. PAM (N) (NS67) 0 0 1 0 1 0 0 0 Pass-Along Sent in either direction to transfer information between two signaling points along the same signaling path as that used to establish a physical connection. PRI (I) (NS67) (NI99) 0 1 0 0 0 0 1 0 Prerelease Information Sent with a release message (REL) in cases where the inclusion of the information in the REL would cause compatibility problems with ISUP 1992 and subsequent versions. REL 0 0 0 0 1 1 0 0 Release Sent in either direction, indicating that the circuit identified in the message is being released. RLC 0 0 0 1 0 0 0 0 Release Complete Sent in either direction as a response to a REL or reset circuit (RSC) message to indicate that the circuit has been brought into the idle state. RSC 0 0 0 1 0 0 1 0 Reset Circuit Sent when an exchange does not know the state of a particular circuit and wants to release any call in progress, remove any remotely blocked state, and align states. RES 0 0 0 0 1 1 1 0 Resume Sent in either direction to indicate reconnection after being suspended (for example, reanswer from an interworking node, or in the case of a non-ISDN, the called party has gone off hook within a certain time after going onhook during the call's active phase). SGM (I) (NS67) 0 0 1 1 1 0 0 0 Segmentation Sent in either direction to convey an additional segment of an over-length message. SAM (I) 0 0 0 0 0 0 1 0 Subsequent Address May be sent in the forward direction following an IAM to convey additional information about the called party number. SDN (N) (I) (NS67) (NI99) 0 1 0 0 0 0 1 1 Subsequent Directory Number May be sent in the forward direction following an IAM to convey additional information about the called party number when the called party number information in the IAM was contained in the Called Directory Number parameter. Typically used in certain number portability scenarios. SUS 0 0 0 0 1 1 0 1 Suspend Sent in the backward direction to indicate that the called party has been temporarily disconnected (for example, a clear back from an interworking exchange, or in case a non-ISDN called party has gone on hook during a call's active state). UBL Unblocking Sent to cancel the blocked condition of a circuit caused by a previously sent BLO 0 0 0 1 0 1 0 0 message. UBA 0 0 0 1 0 1 1 0 Unblocking Acknowledgement Sent in response to a UBL, indicating that the identified circuit is now unblocked. UCIC (N) (NS67) 0 0 1 0 1 1 1 0 Unequipped CIC Sent from one exchange to another when it receives a message that contains an unequipped circuit identification code. UPA (I) (NS67) 0 0 1 1 0 1 0 1 User Part Available Sent in either direction as a response to a user part's test message to indicate that the user part is available. UPT (I) (NS67) 0 0 1 1 0 1 0 0 User Part Test Sent in either direction to test the status of a user part that is marked as unavailable for a signaling point. USR (I) (NS67) 0 0 1 0 1 1 0 1 User-to-User Information Used for transport of user-to-user signaling, independent of call-control messages. KEY: Note that the absence of a symbol beside a message indicates that the message exists in ITU-T ISUP [75 –78], ETSI ISUP [18] and in ANSI ISUP [2]. • (A)— Messages supported in ANSI ISUP [2]only • (I)— Messages not supported in ANSI ISUP [2] • (N)— Messages designated by the ITU-T for national use • (NUK)— Messages not supported by UK ISUP [41] • (NS67)— Messages not supported in ITU-T international ISUP • Q.767 [81] (NI99)— Messages new in ITU-T ISUP 1999 • (NI97)— Messages new in ITU ISUP 1997  . of an outgoing circuit and to transmit number and other information related to the routing and the handling of a call. LPA (N) (NS 67) 0 0 1 0 0 1 0 0 Loop Back Acknowledgement Sent as. Circuit Sent when an exchange does not know the state of a particular circuit and wants to release any call in progress, remove any remotely blocked state, and align states. RES 0 0 0 0 1. (I) (NS 67) 0 0 1 1 0 1 0 1 User Part Available Sent in either direction as a response to a user part& apos;s test message to indicate that the user part is available. UPT (I) (NS 67) 0 0