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ISUP Signaling Information

Overview

This section includes definitions of ISUP messages.

Definitions

The following messages can be modified using the SS7 ISUP Message Format Configure API message. Some messages are marked with a number which indicates the following:

1 Specified for ANSI network

2 Specified for ITU network

3 ITU – for National use

Messages that are not marked with a number indicate use for an ANSI or ITU network.

Signaling Information | Definition
--- | ---
Access Delivery Indicator 2 | Information sent in the backward direction indicating that a SETUP message was generated at the destination access.
Access Transport | Information generated on the access side of a call and transferred transparently in either direction between the originating and terminating local exchanges. The information is of significance to both users and local exchanges.
Address Presentation Restricted Indicator | Information sent in either direction to indicate that the address information is not to be presented to a public network user, but can be passed to another public network.
Address Signal | An element of information in a network address. The address signal may indicate digit values 0 to 9, code 11 or code 12. One address signal value is reserved to indicate end of pulsing of the called party number (ST) and is not used.
Alarm Carrier Indicator 1 | Information sent in either direction indicating the type of carrier alarm handling.
Attendant Status 1 | An indication sent within the business group parameter signifying whether or not the business group information pertains to an attendant line.
Automatic Congestion Level | Information optionally included in a Release Message and sent to the exchange at the other end of a circuit to indicate that a particular level of congestion exists at the sending exchange.
Backward Call Indicators | Information sent in the backward direction consisting of the charge indicator, called party's status indicator, called party's category indicator, end-to-end method indicator, interworking indicator, end-to-end information indicator, ISDN User Part indicator, holding indicator, ISDN access indicator, echo control device indicator, and SCCP method indication.
Business Group 1 | Information sent in either direction to indicate the identity of the Multi-Location Business Group associated with a number (e.g. the Calling Party Number), the identity of a Subgroup within that Multilocation Business Group and the Line Privileges allocated to the number.
Business Group Identifier 1 | Sent within the business group parameter to indicate the identity of the corresponding Multi-location Business Group.
Business Group Identifier Type 1 | Information sent within the business group parameter to indicate the type of business group identification used, e.g. multi-location business group identifier or interworking with private networks identifier.
Call Diversion Information 2 | Information sent in the backward direction indicating the redirection reason and the notification subscription option of the redirecting user.
Call Diversion May Occur Indicator 2 | Information sent in the backward direction indicating that call diversion may occur, depending on the response received (or lack thereof) from the called party.
Call History Information 2 | Information sent in the backward direction to indicate the accumulated propagation delay of a connection.
Call Identity 3 | Information sent in the call reference parameter indicating the identity of a call in a signaling point.
Call Reference 3 | Circuit independent information identifying a particular call.
Called Party Number | Information sent in the forward direction to identify the called party and consisting of the odd/even indicator, nature of address indicator, numbering plan indicator, and address signals.
Called Party’s Category Indicator | Information sent in the backward direction indicating the category of the called party, e.g. ordinary subscriber or pay phone.
Called Party’s Status Indicator | Information sent in the backward direction indicating the status of the called party, e.g. subscriber free.
Calling Party Address Request Indicator 2/3 | Information sent in the backward direction indicating a request for the calling party address to be returned.
Calling Party Address Response Indicator 2/3 | Information sent in response to a request for the calling party address, indicating whether the requested address is included, not included, not available or incomplete.
Calling Party Number | Information sent in the forward direction to identify the calling party and consisting of the odd/even indictor, nature of address indicator, numbering plan indicator, address presentation restriction indicator, screening indicator, and address signals.
Calling Party Number Incomplete Indicator 2/3 | Information sent in the forward direction indicating that the complete calling party number is not included.
Calling Party’s Category | Information sent in the forward direction indicating the category of the calling party, e.g. ordinary subscriber, test call.
Calling Party’s Category Request Indicator 2/3 | Information sent in the backward direction indicating a request for the calling party’s category to be returned.
Calling Party’s Category Response Indicator 2/3 | Information sent in response to a request for the calling party’s category, indicating whether or not the requested information is included in the response.
Carrier Identification Code 1 | Information sent in the forward direction to the transit network indicating the transit network selected by the originating subscriber.
Carrier Selection Information 1 | Sent in the forward direction to indicate whether the calling user selected the transit network by pre-subscription or dialed input and if pre-subscribed whether or not the carrier identification code was also dialed.
Cause Indicators 1 | Information sent in either direction consisting of the coding standard, location, cause value and diagnostics. It indicates the reason for sending the message in which it is contained, e.g. the Release, Address complete or Confusion messages, and identifies the network in which the message originated, e.g. local network, transit network, remote local network.
Cause Value 2 | Information sent in either direction consisting of the coding standard, location, cause value and diagnostics. It indicates the reason for sending the message in which it is contained, e.g. the Release, Address complete or Confusion messages, and identifies the network in which the message originated, e.g. local network, transit network, remote local network.
Charge Indicator | Information sent in the backward direction indicating whether or not the call is chargeable.
Charge Information Request Indicator 2/3 | Information sent in either direction requesting charge information to be returned.
Charge Information Response Indicator 2/3 | Information sent in response to a request for charge information indicating whether or not the requested information is included.
Charge Number 1 | Information sent in either direction indicating the chargeable number for the call and consisting of the odd/even indicator, nature of address indicator, numbering plan indicator, and address signals.
Circuit Assignment Map | Information identifying the map format and the circuits in a multi-rate connection. For the DS 1 map format it identifies the DS0 circuits constituting a NxDS0 connection. The circuit assignment map is used only for NxDS0 calls when non-contiguous time slot allocation is used.
Circuit Group Blocking Type Indicator 1 | Information sent in a Circuit Group Blocking (Unblocking) (Acknowledgment) Message indicating the blocking procedure used.
Circuit Group Carrier Indicator 1 | Information sent in either direction indicating if the circuit group carrier is analog, digital, or analog and digital.
Circuit Group Characteristics Indicator 1 | Information sent in response to a request for circuit validation, indicating the characteristics of the concerned circuit group in terms of carrier type, double seizing control, alarm handling and continuity check requirements.
Circuit Group Supervision Message Type Indicator | Information sent in either direction in a circuit group supervision message and consisting of the circuit group blocking type indicator.
Circuit Identification Code | Information identifying the physical path between a pair of exchanges.
Circuit Identification Name 1 | Information identifying the exchanges on which a circuit group terminates and the number of each trunk within that group.
Circuit State Indicator 3 | Information indicating the state of a circuit according to the sending exchange.
Circuit Validation Response Indicator | Information indicating the far-end results of a circuit validation test.
Closed User Group Call Indicator 2 | Information indicating whether or not the concerned call can be set up as a closed user group call and, if a closed user group call, whether or not outgoing access is allowed.
Closed User Group Interlock Code 2 | Information uniquely identifying a closed user group within a network.
Coding Standard | Information sent in association with a parameter (e.g. cause indicators) identifying the standard in which the parameter format is defined.
Common Language Location Identification (CLLI) 1 | Information used for circuit validation to identify a switching office by town, state, and building subdivision. (COMMON LANGUAGE is a registered trademark and CLLI is a trademark of Bell Communications Research, Inc.)
Component Type 2/3 | There are four types of components that may be present in the Remote Operations parameter. The four Protocol Data Units (PDU) defined in Recommendation X.229 are used. (Invoke, Return Result, Return Error, Reject).
Connected Line Identity Request Indicator 2 | Information sent in the forward direction indicating a request for the connected party number to be returned.
Connected Number 2 | Information sent in the backward direction to identify the connected party.
Connection Request | Information sent in the forward direction on behalf of the Signaling Connection Control Part requesting the establishment of an end-to-end connection and consisting of the local reference, point code, protocol class, and credit.
Continuity Check Indicator | Information sent in the forward direction indicating whether or not a continuity check will be performed on the circuit(s) concerned or is being (has been) performed on a previous circuit in the connection.
Continuity Check Requirement Indicator 1 | Information sent in either direction indicating if and how often a continuity check is required for the circuit group.
Continuity Indicator | Information sent in the forward direction indicating whether or not the continuity check on the outgoing circuit was successful. A continuity check successful indication also implies continuity of the preceding circuits and successful verification of the path across the exchange with the specified degree of reliability.
Credit | Information sent in a connection request, indicating the window size requested by the signaling connection control part for an end-to-end connection.
Diagnostic | Information sent in association with a cause value and which provides supplementary information about the reason for sending the message.
Discard Message Indicator 2 | Information sent to inform another node to discard the related message, due to compatibility reasons.
Discard Parameter Indicator 2 | Information sent to inform another node to discard the related parameter, due to compatibility reasons.
Double Seizing Control Indicator 1 | Information sent in either direction indicating the type of double seizing control applied to the circuit group.
Echo Control Device Indicator | Information sent in the forward direction indicating whether or not an outgoing half echo control device is included in the connection.
Egress Service 1 | Information sent in the forward direction by the first incoming exchange in the terminating exchange area, to indicate network specific attributes associated with the terminating exchange, e.g. the interexchange carrier, the point of interconnection, and type of terminating access service.
Encoding Scheme 2 | Information sent to indicate the coding type for the digit information, e.g. BCD-coded.
End of Optional Parameters 2 | The end of optional parameters field indicates that there are no more optional parameters in the message.
End-to-End Information Indicator | Information sent in either direction indicating whether or not the sending exchange has further call information available for end-to-end transmission.
End-to-End Method Indicator | Information sent in either direction indicating the available methods, if any, for end-to-end transfer of information.
Error Code 2/3 | The error code element contains the reason why an operation cannot be completed successfully. It is present only in a Return Error component. As with operations, errors may be local or global. These errors and associated parameters are defined in relevant supplementary service specifications.
Event Indicator | Information sent in either direction to indicate the type of event that caused a Call Progress message to be sent. Event Information. Information sent in either direction consisting of the event indicator and event presentation restricted indicator that should be relayed to the access. Event Presentation Restricted Indicator. Information sent in either direction to indicate that the occurrence of the concerned event should not be reported to the user.
Event Information 1 | Information sent in either direction consisting of the event indicator and event presentation restriction indicator.
Event Presentation Restricted Indication 3 | Information sent in either direction to indicate that the occurrence of the concerned event should not be reported to the user.
Extension Indicator | Information indicating whether or not the associated octet has been extended.
Facility Indicator 2 | Information sent in facility related messages identifying the facility or facilities with which the message is concerned.
Feature Code 2/3 | Information sent in either direction to invoke, accept, or reject a specific action for a supplementary service.
Feature Code Indicator 1 | Information sent in either direction to invoke a specific feature operation at the terminating or originating CSP.
Filler 2 | A number of bits used to complete a partially used octet to full octet length.
Forward Call Indicators | Information sent in the forward direction consisting of the incoming international call indicator, end-to-end method indicator, interworking indicator, end-to-end information indicator, ISDN User Part indicator, ISDN User Part preference indicator, ISDN access indicator, and SCCP method indicator.
Generic Address 1 | Information in the form of an address pertaining to a supplementary service (e.g., dialed number, destination number) and including type of address, nature of address and numbering plan indications.
Generic Digits 3 | Information in the form of digits pertaining to a supplementary service, (e.g. account code, authorization code, private network class mark) and including type of digits and encoding method indicators.
Generic Name | Information sent in the forward direction containing specific name-related information.
Generic Notification 2 | Information sent in either direction intended to provide supplementary service notification to a user.
Generic Number 2 | A number information sent in either direction to enhance network operation or for supplementary services.
Generic Reference (reserved) 2 | For further study.
Hold Provided Indicator 2/3 | Information sent in the forward direction indicating that the connection will be held after the calling or called party has attempted release.
Holding Indicator 2/3 | Information sent in the backward direction indicating that holding of the connection is requested.
Hop Counter (ITU reserved for further study) | Information sent in the forward direction to minimize the impact of lAM looping. The initial count determines the maximum number of contiguous SS7 interexchange circuits that are allowed to complete the call, assuming all subsequent intermediate exchanges decrement the hop counter.
In-band Information Indicator | Information sent in the backward direction to indicate that in-band information, e.g. a tone or announcement, is present on the circuit path.
Incoming Half Echo Control Device Request Indicator 2 | Information sent to request the activation or deactivation of an incoming half echo control device.
Incoming Half Echo Control Device Response Indicator 2 | Information sent to inform whether an incoming half echo control device has been included or not.
Incoming International Call Indicator 1 | Information sent in the forward direction indicating whether the call is an incoming international or an incoming national call.
Information Indicators | Information sent in either direction consisting of the calling party address response indicator, connected address response indicator, calling party's category response indicator, charge information response indicator, and solicited information indicator.
Information Request Indicators | Information sent in either direction consisting of the calling party address request indicator, connected address request indicator, calling party's category request indicator, charge information request indicator, malicious call identification request indicator, and holding indicator.
Information Transfer Capability 1 | Information sent in the forward direction indicating the type of transmission medium required for the connection.
Information Transfer Rate 1 | Information sent in the forward direction indicating the information transfer rate
Instruction Indicator 2 | Information indicating the reactions to be taken if an unrecognized message or unrecognized parameter is received.
Internal Network Number 2 | Information sent to the destination exchange for specific numbers, e.g. roaming numbers indicating whether or not the network generates the number contained in the parameter.
Interworking Indicator | Information sent in either direction indicating whether or not Signaling System No. 7 is used in all parts of the network connection.
Invoke Identification 2/3 | An Invoke ID is used as a reference number to identify uniquely an operation invocation. It is present in the invoke component and in any reply to the invoke enabling the reply to be correlated with the Invoke.
ISDN Access Indicator | Information sent in either direction indicating whether or not the access signaling protocol is ISDN.
ISDN User Part Indicator | Information sent in either direction to indicate that the ISDN User Part is used in all parts of the network connection.
ISDN User Part Preference Indicator | Information sent in the forward direction indicating whether or not the ISDN User Part is required or preferred in all parts of the network connection. Jurisdiction Information sent in the forward direction indicating the geographic origination of the call.
Jurisdiction Information 1 | Information sent in the forward direction indicating the geographic origination of the call.
Length of Network Identification 2/3) | Information sent in the network specific facility parameter, to indicate the length in octets of the network identification.
Length of Reference Indicator 2 (for further study) | Information sent in the generic reference parameter, to indicate the length in octets of the reference.
Line Privileges 1 | Information sent within the business group parameter to indicate the privileges of the user identified by the corresponding number,
Line Privileges Information Indicator 1 | Information sent within the business group parameter signifying whether the indicated line privileges are standard or customer defined.
Linked Identification 2/3 | A linked ID is included in an Invoke component by a node when it responds to an operation invocation with a linked operation invocation. The node receiving the linked ID uses it for correlation purposes in the same way that it uses the invoke ID in a Return Result, Return Error, or Reject.
Local Reference | Information sent in the connection request, indicating the local reference allocated by the signaling connection control part to an end-to-end connection.
Location 2 | Information sent in either direction indicating where an event was generated.
Location Number 2 | Information sent to indicate the location of a user in the term of an E.164 number.
Look Ahead For Busy 1 | Information sent within the precedence parameter indicating whether the look-ahead for busy option is allowed or whether the path has been reserved.
Look For Busy (LFB) 2 | Information sent in the forward direction to indicate whether LFB option is allowed or if the path for the call is reserved.
Malicious Call Identification Response Indicator 2/3 | Information sent in the forward direction indicating whether the malicious call identification has been provided or not.
MCID Request Indicator 2 | Information sent in the backward direction to request the identity of the calling party for the purpose of malicious call identification.
MCID Response Indicator 2 | Information sent in the forward direction to respond to a MCID request and indicating whether or not the MCID information is available.
Message Compatibility Information Parameter 2 | Information sent in either direction indicating how an exchange should react in case this message is unrecognized.
MLPP Service Domain | Information sent in the precedence parameter identifying the network resources to which the Multi-level Precedence and Preemption supplementary service is applicable for the call.
MLPP User Indicator 2 | Information sent in the backward direction to indicate that the called user is an MLPP user.
National/International Call Indicator 2 | Information sent in the forward direction indicating in the destination national network whether the call has to be treated as an international call or as a national call.
Nature of Address Indicator | Information sent in association with an address indicating the nature of that address, e.g. ISDN international number, ISDN national significant number, or ISDN subscriber number.
Nature of Connection Indicators 1 | Information sent in the forward direction consisting of the satellite indicator, continuity check indicator, and echo control device indicator.
Network Discard Indicator 2 | This indicator indicates that the network has discarded user-to-user information included in the call control message.
Network Identification 1 | Information sent in the forward direction indicating the identity of the transit network.
Network Identification 2/3 | Information sent to identify a network.
Network Identification Plan 1 | Information sent in association with the transit network selection information to identify the type of network identification used. Network Transport A parameter sent in either direction for the purpose of transporting other ISDN User Part parameters transparently across transit exchanges.
Network Identification Plan 2/3 | Information sent to indicate the identification plan for identifying the network, e.g. X.121 or E.212, (DNIC or MNIC).
Network Identity 2/3 | Information sent to identify the network that administrates the supplementary service.
Network Specific Facilities 2/3 | Service related information transparently transferred in either direction between the local exchange and the identified network, which contracts the service. The information is significant to both user and the identified network.
Network Transport | A Parameter sent in either direction for the purpose of transporting other ISDN User Part parameters transparently across transit exchanges.
Notification Indicator 1 | Information Sent in either direction intended to provide supplementary service related notification to a user.
Notification Subscription Option 2 | Information sent in the backward direction indicating that the diversion with or without redirection number can be presented to the calling user.
Number Incomplete Indicator 2 | Information sent in the generic number parameter to indicate whether the delivered number is complete or incomplete.
Numbering Plan Indicator | Information sent in association with an address indicating the numbering plan used for that address (e.g., ISDN numbering plan).
Odd/Even Indicator | Information sent in association with an address, indicating whether the number of address signals contained in the address is even or odd.
Operation Code 2/3 | The operation code element indicates the precise operation to be invoked, and is present in an Invoke component type. It is also present in the Return Result component if the result contains parameters. The operation may be a local or global operation. A local operation can be used in one ASE only. The same global operation can be used in several different ASEs. The actual operation codes, the definition of the operations and their associated parameters, are defined in relevant supplementary service specifications.
Operator Services Information 1 | Information sent in the forward direction between operator services entities primarily identifying charging and service type options.
Optional Backward Call Indicator 1 | Information sent in the backward direction consisting of the in-band information indicator, the call forwarding may occur indicator and the user-network interaction indicator.
Original Called Number | Information sent in the forward direction to indicate, in the case of call redirection (e.g., call forwarding), the number of the user who initiated the initial redirection.
Original Redirecting Reason 1 | Information sent in the forward direction indicating the forwarding condition for the original redirection.
Original Redirection Reason 2 | Information sent in either direction indicating the reason why the call was originally redirected.
Originating Line Information 1 | Information sent in the forward direction, indicating a toll class of service for the call.
Origination ISC Point Code 2 | Information sent in the initial address message of an international call, indicating the point code of the originating ISC.
Outgoing Half Echo Control Device Request Indicator 2 | Information sent to request the activation or deactivation of an outgoing half echo control device.
Outgoing Half Echo Control Device Response Indicator 2 | Information sent to inform whether an outgoing half echo control device has been included or not.
Outgoing Trunk Group Number 1 | Information sent in the backward direction indicating the trunk group selected at an outgoing gateway. For intra-network use only.
Parameter Compatibility Information 2 | Information sent in either direction indicating how an exchange should react in case the parameter is unrecognized.
Party Selector 1 | Information sent within a business group parameter to indicate the type of number to which the business group information applies.
Pass On Not Possible indicator 2 | Information sent to inform another node on what action to take if "pass on" was requested due to compatibility reason but "pass on" was not possible due to interworking with pre-ISUP 1992 signaling.
Point Code | Information sent in the call reference parameter indicating the code of the signaling point in which the call identity allocated to the call reference is relevant.
Precedence 1 | Information sent in the forward direction in association with the invocation of the Multi-Level Precedence and Preemption (MIYP) supplementary service, consisting of the look-ahead for busy indication, the precedence level, network identity, and the MI2P service domain.
Precedence Level 1 | Information sent in the precedence parameter indicating the precedence level of the call.
Precedence Level 2 | Information sent in the forward direction to indicate the priority of the call.
Problem Code 2 | The problem code element contains the reason for the rejection of a component and one such element is present in a Reject component. Four problem code elements are defined (General Problem, Invoke Problem, Return Result Problem, and Return Error Problem.)
Propagation Delay Counter 2 | Information sent in the forward direction to indicate the propagation delay of a connection. This information is accumulated while the parameter is transferred through the network. The propagation delay information is represented by a counter counting in integer multiples of 1 ms.
Protocol Class | Information sent in the connection request parameter indicating the protocol class requested by the signaling connection control part for the end-to-end connection
Protocol Control Indicator 1 | Information consisting of the end-to-end method indicator, the interworking indicator, the end-to-end information indicator and the ISDN User Part indicator. The protocol control indicator is contained in both the forward and backward call indicators parameter fields and describes the signaling capabilities within the network connection.
Protocol Control Indicator 2 | Information consisting of the end-to-end method indicator, the interworking indicator, the SCCP Method indicator and the ISDN User Part indicator. The protocol control indicator is contained in both the forward and backward call indicators parameter fields and describes the signaling capabilities within the network connection.
Protocol Profile 2/3 | Information sent in either direction to indicate the protocol used in the Remote Operations parameter.
Range | Information sent in a circuit group supervision message (e.g. Circuit Group Blocking) to indicate the range of circuits affected by the action in the message.
Range and Status 1 | Information sent in either direction in circuit group supervision messages consisting of the range and status.
Redirecting Indicator 2 | Information sent in either direction indicating whether the call has been diverted or rerouted and whether or not presentation of redirection information to the calling party is restricted.
Redirecting Number | Information sent in the forward direction indicating the number from which the call was last redirected and consisting of the nature of address indicator, numbering plan indicator, address presentation restriction indicator, and address information (signals).
Redirecting Reason | Information sent in the forward direction indicating the forwarding condition for the last redirection.
Redirection Counter | Information sent in the forward direction indicating the number of forwardings undergone.
Redirection Indicator 2 | Information sent to indicate whether the call has undergone diversion or rerouting. It also contains information about presentation restrictions.
Redirection Information | Information sent in the forward direction consisting of the original redirecting reason redirection counter and redirecting reason.
Redirection Number 2 | Information sent in the backward direction indicating the number towards which the call must be rerouted or has been forwarded.
Redirection Number Restriction Indicator 2 | Information sent in the backward direction indicating whether the diverted-to user allows the presentation of his number.
Redirection Reason 2 | Information sent in the call diversion information parameter and the redirection information parameter to indicate the reason for the redirection.
Reference nth Octet 2 (for further study) | Information sent in the generic reference parameter, expressing the reference number of the context given by the entity, which handles and provides the service.
Reference Qualifier Indicator 2 (for further study) | Information sent in the generic reference parameter, identifying the context that handles and provides service.
Release Call Indicator 2 | Information sent to inform another node to release the call or not, by compatibility reasons, if the related message or parameter is unrecognized.
Remote Operations 3 | The remote operations parameter is used to indicate the invocation of a supplementary service identified by an operation value and also carry the result or error indications depending on the outcome of the operation.
Routing Label | Information provided to the message transfer part for the purpose of message routing.
Satellite Indicator | Information sent in the forward direction indicating the number of satellite circuits in the connection.
SCCP Method Indicator | Information sent in the forward direction indicating the available SCCP methods, if any, for end-to-end transfer of information.
Screening Indicator | Information sent in association with a number indicating whether the number was network or user provided, and if user provided, whether the network views the number as correctly identifying the user.
Send Notification Indicator 2 | Information sent to inform another node to send notification, due to compatibility reason, if the related message or parameter is unrecognized.
Sequence 2/3 | The sequence is an ordered set.
Service Activation 1 | Information sent in either direction to indicate the invocation of one or more supplementary services.
Service Activation Parameter 2/3 | Information sent in either direction to indicate the invocation, acceptance or rejection of supplementary services, when no service associated parameter is to be sent.
Service Code | Information sent in the forward direction indicating a service code provided by the calling party.
Set 2/3 | The Set element is used to contain a set of information elements accompanying a component. It is required in the case of more than one information element being included in a component. The information elements themselves are defined in relevant supplementary service specifications.
Signaling Point Code 2/3 | Information sent in a release message to identify the signaling point in which the call failed.
Simple Segmentation Indicator 2 | Information sent in either direction to indicate that additional information will be forwarded in an information message (unsolicited).
Solicited Information Indicator | Information sent in an information message to indicate whether or not the message is a response to an information request message
Special Processing Request 1 | Information sent in the forward direction from a private network access node to service node in the public switched network to indicate that the call requires special processing at that node e.g. private network number translation or verification of authorization codes.
Status | Information sent in a circuit group supervision message (e.g. Circuit Group Blocking) to indicate the specific circuits, within the range of circuits stated in the message, that are affected by the action specified in the message.
Sub-Group Identifier 1 | Information sent within a business group parameter to indicate the identity of the subgroup of which the user identified by the corresponding number is a member.
Suspend/Resume Indicator | Information sent in the Suspend and Resume Messages to indicate whether suspend/resume was initiated by an ISDN subscriber or by the network.
Suspend/Resume Indicators 1 | Information sent in either direction consisting of the suspend/resume indicator
Temporary Trunk Blocking After Release 2/3 | Information sent to the exchange at the other end of a circuit (trunk) to indicate low level of congestion at the sending exchange and that the circuit (trunk) should not be re-occupied by the receiving exchange for a short period of time after release.
Transaction Request 1 | Information sent in the Initial Address Message (lAM) to help continue call processing, using Transaction Capabilities (TC), associated with a given call during an assist or hand-off procedure.
Transfer Mode 1 | Information sent in the forward direction indicating circuit or packet transfer mode.
Transit at Intermediate Exchange Indicator 2 | Information sent to inform a transit node (Type B), whether it shall react on the rest of the instruction indicators or not, if the related message or parameter is unrecognized.
Transit Network Selection 3 | Information sent in the forward direction indicating the transit network(s) requested for the routing of the call and consisting of the type of network identification, network identification plan, and network identification.
Transmission Medium Requirement 2 | Information sent in the forward direction indicating the type of transmission medium required for the connection (e.g. 64Kbps unrestricted speech).
Transmission Medium Requirement Prime 2 | Information sent in the forward direction indicating the fallback connection type in case of fallback.
Transmission Medium Used | Information sent in the backward direction indicating the resulting fallback connection type used for a call after the fallback has occurred.
Trunk Number 1 | Information used for circuit validation to identify the trunk number of the Common Language circuit identification.
Type Indicator 2 | Information sent to indicate the initiator for a circuit group supervision message, e.g., maintenance-oriented or hardware failure-oriented.
Type of Address 1 | Information that specifies the type of address digits contained in a Generic Address parameter.
Type of Digits 3 | Information that specifies the type of digits contained in a Generic Digits parameter.
Type of Network Identification 1 | Information sent in the forward direction indicating the format of the transit network identification.
Type of Network Identification 2/3 | Information sent to inform whether the identification of a network is by CCITT (ITU) standardization identification or by national network identification.
User Service Information | Information sent in the forward direction indicating the bearer capability requested by the calling party and including as a minimum, the coding standard and information transfer capability, transfer mode, and information transfer rate.
User Service Information Prime | Information sent in the forward direction indicating the preferred bearer capability requested by the calling party.
User Teleservice Information 2 | Information sent in the initial address message indicating the Higher Layer Compatibility information requested by the calling party.
User-Network Interaction Indicator 1 | Information sent in the backward direction to indicate that the sending exchange is collecting additional information from the calling party before routing the call further.
User-to-User Indicators | Information sent in association with the response to a request for user-to-user signaling supplementary service(s).
User-to-User Information | Information generated by a user and transferred transparently through the intermediate exchanges between the originating and terminating local exchanges.

See Integrated Services Digital Network User Part.
See Signaling System Number Seven.
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)
See Integrated Services Digital Network.
The condition of a component at a given instant. The current "context" of a PPL object, such as Idle, Seizing, Answered. In PPL files, a State is represented by a circle.
PDU. Used by bridges to transfer connectivity informa-tion.
SCCP. The signaling connection and control part of the SS7 signaling protocol. For example, performs Global Title Translations (GTT), Subsystem Management.
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.
Interworking is a software feature within the Excel platform call control layer that enables protocol conversion by analyzing and converting Network Signaling (NS) Layer 3 information.
Address format for ISDN networks. The international public telecom-munications numbering plan. A standard set by ITU-T for addressing telephone numbers. See ITU Recommendation E.164 (1991).
A number that addresses a node in a SS7 network.
Comité Consultatif Internationale de Telephonique et Telegraphique (now ITU)