ACM (Address Complete Message) An Address Complete Message (ACM) is sent in the "backward" direction to indicate that the remote end of a trunk circuit has been reserved. The originating switch responds to an ACM message by connecting the calling party's line to the trunk to complete the voice circuit from the calling party to the called party. The terminating switch sends a ringing tone to the calling party's line.
Parameter	Type	Length (octet)
Message type	F	1
Backward Call Indicators	F	2
Optional Backward Call Indicators	O	3
Call Reference	O	7
Cause Indicators	O	4-?
User to User Indicators	O	3
User to User Information	O	3-131
Access Transport	O	3-?
Generic Notification Indicator	O	3
Transmission Medium Used	O	3
Echo Control Information	O	3
Access Delivery Information	O	3
Redirection Number	O	5-12
Parameter Compatibility Information	O	4-?
Call Diversion Information	O	3
Network Specific Facility	O	4-?
Remote Operations	O	3-?
Service Activation	O	3-?
Redirection Number Restriction	O	3
End of Optional Parameters	O	1

ANM (Answer Message) When the called party answers, the destination switch terminates power ringing of the called line, removes audible ringing tone from the calling line and sends an Answer Message (ANM) to the originating switch. The originating switch initiates billing after verifying that the calling party's line is connected to the reserved trunk.
Parameter	Type	Length (octet)
Message type	F	1
Backward Call Indicators	O	4
Optional Backward Call Indicators	O	3
Call Reference	O	7
User to User Indicators	O	3
User to User Information	O	3-131
Connected Number	O	4-12
Access Transport	O	3-?
Generic Notification Indicator	O	3
Call History Information	O	4
Transmission Medium Used	O	3
Generic Number	O	4-12
Echo Control Information	O	3
Access Delivery Information	O	3
Redirection Number	O	5-12
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	4-?
Remote Operations	O	3-?
Service Activation	O	3-?
Redirection Number Restriction	O	3
End of Optional Parameters	O	1

Call Progress Message (CPG) CPG is sent in either direction during the set-up or active phase of the call, indicating that an event, which is of significance, and should be relayed to the originating or terminating access, has occurred.
Parameter	Type	Length (octet)
Message type	F	1
Event Information	F	1
Cause Indicators	O	4-?
Backward Call Indicators	O	4
Optional Backward Call Indicators	O	3
Call Reference	O	7
User to User Indicators	O	3
User to User Information	O	3-131
Connected Number	O	4-12
Access Transport	O	3-?
Generic Notification Indicator	O	3
Call Diversion Information	O	3
Transmission Medium Used	O	3
Access Delivery Information	O	3
Redirection Number	O	5-12
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	4-?
Remote Operations	O	3-?
Service Activation	O	3-?
Redirection Number Restriction	O	3
End of Optional Parameters	O	1

Circuit Group Response Message (CQR) Sent in response to a Circuit/CIC Group Query message to indicate the state of all circuits/CICs in a particular range.
Parameter	Type	Length (octet)
Message type	F	1
Range and Status	V	2
Circuit State Indicator	V	3-33

Circuit Group Reset Acknowledgement Message (GRA) GRA is sent in response to a Circuit/CIC Group Reset message indicating that the requested group of circuits/CICs has been reset. The message also indicates the maintenance blocking state of each circuit/CIC.
Parameter	Type	Length (octet)
Message type	F	1
Range and Status	V	3-34

Confusion Message (CFN) CFN is sent in response to any message (other than a confusion message) if the node does not recognize the message or detects a part of the message as being unrecognized.
Parameter	Type	Length (octet)
Message type	F	1
Cause Indicators	V	4-20
End of Optional Parameters	O	1

Connect Message (CON) CON is sent in the backward direction indicating that all the address signals required for routeing the call to the called party have been received and that the call has been answered.
Parameter	Type	Length (octet)
Message type	F	1
Backward Call Indicators	O	2
Optional Backward Call Indicators	O	3
Call Reference	O	7
User to User Indicators	O	3
User to User Information	O	3-131
Connected Number	O	4-12
Access Transport	O	3-?
Generic Notification Indicator	O	3
Call History Information	O	3
Transmission Medium Used	O	3
Generic Number	O	4-12
Echo Control Information	O	3
Access Delivery Information	O	3
Redirection Number	O	5-12
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	4-?
Remote Operations	O	?
Service Activation	O	3-?
Redirection Number Restriction	O	3
End of Optional Parameters	O	1

Continuity Message (COT) COT is sent in the forward direction indicating whether or not there is continuity on the preceding circuit(s) as well as of the selected circuit to the following exchange, including verification of the communication path across the exchange with the specified degree of reliability.
Parameter	Type	Length (octet)
Message type	F	1
Continiuty Indicators	F	1

Facility Reject Message (FRJ) FRJ is sent in response to a facility request message to indicate that the facility request has been rejected.
Parameter	Type	Length (octet)
Message type	F	1
Facility Indicators	F	1
Cause Indicators	V	4
User to User Indicators	O	3
End of Optional Parameters	O	1

Information Message (INF) INF is sent to convey information in association with a call, which may have been requested in an information request message.
Parameter	Type	Length (octet)
Message type	F	1
Information Indicators	F	2
Calling Party's Category	O	3
Calling Party Number	O	5-12
Call Reference	O	7
Connection Request	O	7-9
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	6-?
End of Optional Parameters	O	1

Information Request Message (INR) INF is sent by a node to request information in association with a call.
Parameter	Type	Length (octet)
Message type	F	1
Information Request Indicators	F	2
Call Reference	O	7
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	4-?
End of Optional Parameters	O	1

IAM (Initial Address Message) An Initial Address Message (IAM) is sent in the "forward" direction by each switch needed to complete the circuit between the calling party and called party until the circuit connects to the destination switch. An IAM contains the called party number in the mandatory variable part and may contain the calling party name and number in the optional part.
Parameter	Type	Length (octet)
Message type	F	1
Nature of Connection Indicators	F	1
Forward Call Indicators	F	2
Calling Party's Category	F	1
Transmission Medium Requirement	F	1
Called Party Number	V	4-11
Transit Network Selection	O	4-?
Call Reference	O	7
Calling Party Number	O	4-12
Optional Forward Call Indicators	O	3
Redirecting Number	O	4-12
Redirection Information	O	3-4
Closed User Group Interlock Code	O	6
Connection Request	O	7-9
Origional Called Number	O	4-12
User to User Information	O	3-131
Access Transport	O	3-?
User Service Information	O	4-13
User to User Indicators	O	3
Generic Number	O	5-13
Propagation Delay Counter	O	4
User Service Information Prime	O	4-13
Network Specific Facility	O	4-?
Generic Digit	O	?
Originating ISC Point Code	O	4
User Service Information Prime	O	7
Remote Operations	O	?
Parameter Compatibility Information	O	4-?
Generic Notification	O	3
Service Activation	O	3-?
Generic Reference	O	5-?
MLPP Precedence	O	8
Transmission Medium Requirement Prime	O	3
Location Number	O	5-12
End of Optional Parameters	O	1

REL (Release Message) A Release Message (REL) is sent in either direction indicating that the circuit is being released due to the cause indicator specified. An REL is sent when either the calling or called party "hangs up" the call (cause = 16). An REL is also sent in the backward direction if the called party line is busy (cause = 17).
Parameter	Type	Length (octet)
Message type	F	1
Cause Indicators	V	3-?
Redirection Information	O	3-4
Redirection Number	O	5-12
User to User Indicators	O	3
User to User Information	O	3-131
Access Transport	O	3-?
Access Delivery Information	O	3
Parameter Compatibility Information	O	4-?
Network Specific Facility	O	4-?
signalingPoint Code	O	4
Automatic Congestion Level	O	4
Redirection Number Restriction	O	3
End of Optional Parameters	O	1

Release Complete Message A Release Complete Message (RLC) is sent in the opposite direction of the REL to acknowledge the release of the remote end of a trunk circuit and end the billing cycle as appropriate.
Parameter	Type	Length (octet)
Message type	F	1
Cause Indicators	O	5-6
End of Optional Parameters	O	1

Subsequent Address Message (SAM) SAM is sent in the forward direction following an initial address message, to convey additional called party number information.
Parameter	Type	Length (octet)
Message type	F	1
Subsequent Number	V	3-10
End of Optional Parameters	O	1

User to User Information Message (USR) USR is used for the transport of user to user signalingindependent of call control messages.
Parameter	Type	Length (octet)
Message type	F	1
User to User Information	V	2-130
Access Transport	O	3-?
End of Optional Parameters	O	1

Forward Transfer  Message (FOT) A message sent in the forward direction on semi automatic calls when the outgoing international exchange operator wants the help of an operator at the incoming international exchange. The message will normally serve to bring an assistance operator into the call if the call is automatically set up at the exchange.
Parameter	Type	Length (octet)
Message type	F	1
Call Reference	O	7
End of Optional Parameters	O	1

Resume (RES), Suspend (SUS) Messages RES is sent in either direction indicating that the calling or called party, after having been suspended, is reconnected. SUS is sent in either direction indicating that the calling or called party has been temporarily disconnected.
Parameter	Type	Length (octet)
Message type	F	1
Suspend, Resume Indicators	F	1
Call Reference	O	7
End of Optional Parameters	O	1

Blocking (BLO) , Blocking Acknowledgement (BLA), Continuity Check Request (CCR) , Loop Back Acknowledgement (LPA), Overload (OLM), Reset Circuit (RSC), Unblocking (UBL), Unblocking Acknowledgement (UBA), Unequipped Circuit Identification Code (UCIC) Blocking (BLO) message sent only for maintenance purposes to the exchange at the other end of a circuit, to cause an engaged condition of that circuit for subsequent calls outgoing from that exchange. When a circuit is used in the bothway mode of operation, an exchange receiving the blocking message must be capable of accepting incoming calls on the concerned circuit unless it has also sent a blocking message. Under certain conditions, a blocking message is also a proper response to a reset circuit message. Blocking Acknowledgement (BLA) message sent in response to a blocking message indicating that the circuit has been blocked. Continuity Check Request (CCR) message sent by an exchange for a circuit on which a continuity check is to be performed, to the exchange at the other end of the circuit, requesting continuity checking equipment to be attached. Loop Back Acknowledgement (LPA) message sent in the backward direction in response to a continuity check request message indicating that a loop (or transceiver in the case of a 2-wire circuit) has been connected. Overload (OLM) 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. Reset Circuit (RSC) message sent to release a circuit/CIC when, due to memory mutilation or other causes, it is unknown whether for example, a Release or a Release Complete message is appropriate. If, at the receiving end, the circuit/CIC is remotely blocked, reception of this message should cause that condition to be removed. Unblocking (UBL) message sent to the exchange at the other end of a circuit to cancel, in that exchange, the engaged condition of the circuit caused by a previously sent blocking or circuit group blocking message. Unblocking Acknowledgement (UBA) message sent in response to an unblocking message indicating that the circuit has been unblocked. Unequipped Circuit Identification Code (UCIC) message sent from one node to another when it receives a message on a circuit/CIC that is not provisioned for use.
Parameter	Type	Length (octet)
Message type	F	1

Circuit Group Blocking (CGB), Circuit Group Blocking Ack. (CGBA), Circuit Group Unblocking (CGU), Circuit Group Unblocking Ack. (CGUA)  Messages Circuit Group Blocking (CGB) message sent to the node to permit the switching equipment or maintenance system to remove from (and return to) traffic a group of circuits/CICs. A node receiving a Circuit/CIC Group Blocking message must be able to accept incoming calls on the group of blocked circuits/CICs unless it has also sent a Circuit/CIC Group Blocking message. Circuit Group Blocking Acknowledgement (CGBA) message sent in response to a Circuit/CIC Group Blocking message to indicate that the requested group of circuits/CICs has been blocked. Circuit Group Unblocking (CGU) message sent to the node to cause cancellation in a group of circuits/CICs of a blocked condition invoked earlier by a Circuit/CIC Group Blocking message. Circuit Group Unblocking Acknowledgement (CGUA) message sent in response to a Circuit/CIC Group Unblocking message to indicate that the requested group of circuits/CICs has been unblocked.
Parameter	Type	Length (octet)
Message type	F	1
Circuit group supervision message type indicators	F	1
Range and Status	V	3-34

Circuit Group Reset (GRS), Circuit Group Query (CQM) Messages Circuit Group Reset (GRS) message sent to release an identified group of circuits/CICs when, due to memory mutilation or other causes, it is unknown whether for example, a release or release complete message is appropriate for each of the circuits/CICs in the group. If at the receiving end a circuit/CIC is remotely blocked, reception of this message should cause that condition to be removed. Circuit Group Query (CQM) message sent on a routine or demand basis to request the far-end node to give the state of all circuits/CICs in a particular range.
Parameter	Type	Length (octet)
Message type	F	1
Range and Status	V	2

Facility Accepted (FAA), Facility Request (FAR) Messages Facility Accepted (FAA) message sent in response to a facility request message indicating that the requested facility has been invoked. Facility Request (FAR) message sent from a node to another node to request activation of a facility.
Parameter	Type	Length (octet)
Message type	F	1
Facility Indicators	F	1
Call Reference	O	7
User to User Indicators	O	3
Connection Request	O	9
Parameter Compatibility Information	O	4-?
End of Optional Parameters	O	1

Pass-along (PAM) Message Pass-along (PAM) message that may be sent in either direction to transfer information between two signalingpoints along the same signalingpath as that used to establish a physical connection between those two points.
Parameter	Type	Length (octet)
Message type	F	1

User Part Test (UPT), User Part Available (UPA) Messages User Part Test (UPT) message sent in either direction to test the status of a user part marked as unavailable for a signalingpoint. User Part Available (UPA) message sent in either direction as a response to a user part test message, to indicate that the user part is available.
Parameter	Type	Length (octet)
Message type	F	1
Parameter Compatibility Information	O	4-?
End of Optional Parameters	O	1

Facility (FAC) Message Facility (FAC) message sent in either direction at any phase of the call to request an action at another node. The message is also used to carry the results, error or rejection of a previously requested action.
Parameter	Type	Length (octet)
Message type	F	1
Service Activation	O	3-?
Remote Operations	O	?
Message Compatibility Information	O	4
Parameter Compatibility Information	O	4-?
End of Optional Parameters	O	1

Network Resorce Management (NRM) Message Network Resource Management (NRM) message sent in order to modify network resources associated with a certain call. The message is sent along an established path in any direction in any phase of the call.
Parameter	Type	Length (octet)
Message type	F	1
Echo Control Information	O	3
Transmission Medium Used	O	3
Message Compatibility Information	O	4
Parameter Compatibility Information	O	4-?
End of Optional Parameters	O	1

Identification Request (IDR) Message Identification Request (IDR) message sent in the backward direction to request action regarding the malicious call identification supplementary service.
Parameter	Type	Length (octet)
Message type	F	1
MCID Request Indicators	O	3-?
Message Compatibility Information	O	4-?
Parameter Compatibility Information	O	4-?
End of Optional Parameters	O	1

Identification Response (IRS) Message Identification Response (IRS) message sent in response to the identification request message.
Parameter	Type	Length (octet)
Message type	F	1
MCID Response Indicators	O	3-?
Message Compatibility Information	O	4-?
Parameter Compatibility Information	O	4-?
Calling Party Number	O	5-12