SS7 ISUP Messages

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.

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.

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.

Sent in response to a Circuit/CIC Group Query message to indicate the state of all circuits/CICs in a particular range.

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.

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.

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.

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.

FRJ is sent in response to a facility request message to indicate that the facility request has been rejected.

INF is sent to convey information in association with a call, which may have been requested in an information request message.

INF is sent by a node to request information in association with a call.

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.

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).

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.

SAM is sent in the forward direction following an initial address message, to convey additional called party number information.

USR is used for the transport of user to user signaling independent of call control messages.

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.

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.

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.

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.

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.

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.

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.

User Part Test (UPT) message sent in either direction to test the status of a user part marked as unavailable for a signaling point.

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.

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.

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.

Identification Request (IDR) message sent in the backward direction to request action regarding the malicious call identification supplementary service.

Identification Response (IRS) message sent in response to the identification request message.

Segmentation (SGM) message sent in either direction to convey an additional segment of an overlength message.