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ISUP Signaling Messages

Message Code | ID | Description | Purpose
ACM | 0x06 | Address Complete Message | Sent in the backward direction indicating that all required data has been received and the call set-up is progressing
ANM | 0x09 | Answer Message | Sent in the backward direction to indicate that the called party has answered the call, may be used to trigger billing and call
BLA | 0x15 | Blocking Acknowledgment | Sent as a response to a BLO message indicating the identified circuit has
BLO 1 | 0x13 | Blocking | Sent for maintenance purposes to the exchange at the other end of the circuit to cause an engaged condition of that circuit (receive only)
CCL |  | Calling Party Clear |
CCR | 0x11 | Continuity Check Request | Sent to request a non-call-related continuity check on the identified circuit
CFN | 0x2F | Confusion | Sent in response to any message (other than a confusion message) to indicate that all or part of a received message was unrecognized
CGB | 0x18 | Circuit Group Blocking | Sent for maintenance purposes to the exchange at the far end of a group of circuits to cause the engaged condition of those circuits
CGBA | 0x1A | Circuit Group Blocking Acknowledgment | Sent as a response to a CGB indicating that the identified group of circuits has been blocked to outgoing traffic
CGU | 0x19 | Circuit Group Unblocking | Sent to cancel the engaged condition of a group of circuits caused by a previously sent CGB message.
CGUA | 0x1B | Circuit Group Unblocking Acknowledgment | Sent in response to a CGU indicating the identified group of circuits are now in the idle state
CMC 3 | 0x1D | Call Modification Complete | Message sent in either direction to indicate that the call modification request has been accepted
CMR3 | 0x1C | Call Modification Request | Message sent in either direction to request a change in the call characteristics
CMRJ 3 | 0x1E | Call Modification Reject | Message sent in either direction to indicate that the call modification request has been rejected
CON 2 | 0x0F | Connect | Sent in the backward direction indicating that all the address signals required for routing the call to the called party have been received and that the call has been answered
COT | 0x05 | Continuity | Sent in the forward direction to indicate the result of the completed continuity test
CPG | 0x2C | Call Progress | Sent in either direction indicating that an event of significance to the originating or terminating access has occurred
CQM 3 | 0x2A | Circuit Query Message | Sent on a routine or demand basis to request the exchange at the other end of a group of circuits give the state of the circuits within the specified range
CQR 3 | 0x2B | Circuit Query Response | Sent in response to a CQM indicating the state of the previously identified group of circuits.
CRA 1 | 0xE9 | Circuit Reservation Acknowledgment | Sent in the backward direction in response to a CRM indicating that the circuit has been reserved for an incoming call
CRG 2 | 0x31 | Charge Information | Information sent in either direction for accounting and/or call charging purposes. national use only
CRM 1 | 0xEA | Circuit Reservation Message | Sent in the forward direction only when interworking with exchange access MF signaling to reserve a circuit and initiate any required continuity check
CVR 1 | 0xEB | Circuit Validation Response | Sent in response to a CVT to convey translation information for the indicated circuit
CVT 1 | 0xEC | Circuit Validation Test | Sent on a routine or demand basis to request translation information for the identified circuit
DRS 2/3 | 0x27 | Delayed Release | Sent in either direction to indicate that the called or calling party has disconnected while the network is still holding the connection
En-block calls |  | Address digits are transmitted in one or more blocks. | In this form of signaling, address digits are transmitted in one or more blocks, and each block contains enough address information to enable the CSP to carry out forward routing.
EXM 1 | 0xED | Exit Message | Sent in the backward direction from an outgoing gateway exchange to indicate that the call has successfully progressed to the adjacent network
FAA 2 | 0x20 | Facility Accept | Sent in response to a facility request message indicating that the requested facility has been invoked
FAC 3 | 0x33 | Facility Message | 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
FAR 2 | 0x1F | Facility Request | Sent from one exchange to another to request activation of a facility
FOT | 0x08 | Forward Transfer | Sent in the forward direction on semi-automatic calls when the operator wants the help of an operator at a distant exchange
FRJ 2 | 0x21 | Facility Reject | Sent in response to a facility request message indicating that the facility request has been rejected
GRA | 0x29 | Circuit Group Reset Acknowledgment | Sent in response to a GRS message to indicate the group of circuits have been realigned
GRS | 0x17 | Circuit Group Reset | Sent to align the state of a group of circuits, release any calls in progress remove any remotely blocked state.
IAM | 0x01 | Initial Address Message | Sent in the forward direction to initiate seizure of an outgoing circuit. May also request continuity test on identified circuit
IDR 2 | 0x36 | Identification Request | Sent in either direction to request an action regarding the malicious call identification supplementary service
IDS 2 | 0x37 | Identification Response | Sent in response to the identification request message
INF 3 | 0x04 | Information | Sent to convey additional call-related information which may have been requested in the inr message
INR 3 | 0x03 | Information Request | Sent by an exchange to request additional call related information
IRS |  | Identification |
LPA 3 |  | Loopback Acknowledge |
MCP |  | Message Compatibility Procedure |
MPM |  | Meter Pulse Message |
NRM 2 |  | Network Resource Management | Sent in order to modify network resources associated with a certain call, sent along an established path in any direction in any phase of a call
OLM 2/3 |  | Overload Message | Sent in the backward direction, on non-priority calls in response to an iam, to invoke temporary trunk blocking of the circuit concerned when the exchange generating the message is subject to load control
OPR |  | Operator |
PAM 3 | 0x28 | Pass Along Message | Sent in either direction to transfer information between two signaling points along the same signaling path as that used to establish a physical connection.
PCP |  | Parameter Compatibility procedure |
PDC |  | Propagation Delay Counter |
REL | 0x0C | Release | Sent in either direction indicating that the circuit identified in the message is being released and the cause for the release
RES | 0x0E | Resume | Sent in the backward direction to indicate re-answer from an interworking node or that a non-ISDN called party has gone off hook
RLC | 0x10 | Release Complete | Sent in either direction as a response to a release message or a reset circuit message to indicate that the circuit has been brought into the idle state
RSC | 0x12 | 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
SAM 2 | 0x02 | Subsequent Address Message | Sent in the forward direction to convey an additional segment of an overlength message after the IAM and before the ACM.
SGM 2 | 0x38 | Segmentation Message | Sent in either direction to convey an additional segment of an overlength message
SUS | 0x0D | Suspend | Sent in the backward direction to indicate clear back from an interworking exchange or a non-ISDN called party has gone on hook
TTB |  | Temporary Trunk Blocking |
UBA | 0x16 | Unblocking Acknowledgment | Sent in response to a UBL indicating the identified circuit is now in the idle state
UBL | 0x14 | Unblocking | Sent to cancel the engaged condition of a circuit caused by a previously sent BLO message
UCIC 3 | 0x2E | Unequipped CIC | Sent from one exchange to another when it receives a message that contains an unequipped circuit identification code
UPA 2 | 0x35 | User Part Available | Sent in either direction as a response to a user part test message, to indicate that the user part is available
UPT 2 | 0x34 | User Part Test | Sent in either direction to test the status of a user part marked as independent of call control messages
USR 2 | 0x2D | User-Defined | Used for transport of user-to-user signaling independent of call control messages

1 Messages supported in ANSI only

2 Messages supported in ITU only

3 ITU - National use

Blocking Acknowldgment message
Continuity Check Request message (ISUP)
In PPL, a condition that, when met, drives a state machine (PPL Component) from one state to another, by invoking an associated Primitive. In PPL files, an Event is marked by an arrow and text.
Multi-Frequency
A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through a data communications link or network.
See Integrated Services Digital Network.
See Circuit Identification Codes.
American National Standards Institute. ANSI administers and coordinates the U.S. voluntary standardization and conformity assessment system for the
telecommunications industry. More details on these standards may be
viewed at www.ansi.org.
International Telecommunications Union (UN)