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TCAP Messages

Introduction

The SIGTRAN Application (SigtranApp) uses TCAP messages to pass inbound and outbound TCAP content internally over the n2svcd message bus.

The following applications from the core n2svcd module use SigtranApp.

TesterApp (initates outbound MAP/INAP/CAMEL dialogs)
ScriptApp (handles inbound MAP/INAP/CAMEL dialogs)

The following LuaApp services from the core n2svcd module use SigtranApp.

ProcessUssdLuaService (handles inbound MAP dialogs)

The following applications from the n2sip module use SigtranApp.

MssApp (initates outbound INAP/CAMEL dialogs)
SrpApp (handles outbound INAP/CAMEL dialogs)

The internal TCAP messages are:

TCAP-RECV
TCAP-SEND
TCAP-SENT
TCAP-FAIL
TCAP-PREARRANGED-END
TCAP-TRANSFER
TCAP-TXNCHECK-REQUEST
TCAP-TXNCHECK-RESPONSE

Note that this page uses the term “on-the-wire” to refer to the sending or receiving of TCAP content by the SigtranApp. This term is also inclusive of the case where the message is sent by local loopback and does not physically transit a Network Interface Controller (NIC).

Context for TCAP Messages

Note that when using send_message to send TCAP-… internal messages across the IPC message bus, the contexts are non-standard.

The context for the SigtranApp is the Local TID in hex format (if confirmed).

The “Other App” context is “|” e.g. “424|ssp.scp”.

Message	Sender Context	Recipient Context
`TCAP-RECV` (BEGIN, Uncorrelated) SigtranApp -> Other App	New Local TID	`undef`
`TCAP-RECV` (BEGIN, Correlated, e.g. ARI) SigtranApp -> Other App	New Local TID	"\|" For previous transaction.
`TCAP-RECV` (non-BEGIN) SigtranApp -> Other App	Local TID	"\|"
`TCAP-SEND` (BEGIN) Other App -> SigtranApp	"\|"	New Local TID
`TCAP-SEND` (non-BEGIN) Other App -> SigtranApp	"\|"	Existing Local TID
`TCAP-FAIL` `TCAP-SENT`	Local TID (iff present in `TCAP-SEND`)	"\|"
`TCAP-TXNCHECK-REQUEST` SigtranApp -> Other App	Existing Local TID	"\|"
`TCAP-TXNCHECK-RESPONSE` Other App -> SigtranApp	"\|"	Existing Local TID

TCAP-RECV

The TCAP-RECV message is generated by SigtranApp and sent to the receiving app when an inbound TCAP message is received over the SIGTRAN interface. The SigtranApp is responsible for determining which application should receive the TCAP.

For a TCAP BEGIN, this is done using the handlers configuration which will examine the originator, and/or the SCCP SSN, and/or may perform inspection of the user content.

For a TCAP non-BEGIN, there must be an existing context for the Local Transaction ID (TID).

Refer to the SigtranApp Configuration documentation for more information on handling and routing of TCAP-BEGIN within SigtranApp.

The receiving application is responsible for deciding how to process the TCAP-RECV when it arrives. Refer to the documentation for the receiving application.

The attributes of the TCAP-RECV message are:

Field	Type	Description
`type`	`BEGIN`, `CONTINUE`, `END`, `ABORT`	[Required] One of the specified constant string types.
`remote_sccp`	SCCP Address Object	[BEGIN, Required] The far-end SCCP address as received in this TCAP message. See below for definition of the structure for all local_sccp and remote_sccp elements.
`local_sccp`	SCCP Address Object	[BEGIN, Required] Our local SCCP address as received in this TCAP message. See below for definition of the structure for all local_sccp and remote_sccp elements.
`remote_tid`	Hex String	[BEGIN/CONTINUE, Required] Far-end transaction ID in hexadecimal format.
`local_tid`	Hex String	[Required] Local transaction ID in hexadecimal format. For `type` = `BEGIN` this is assigned locally by SigtranApp. For other `type` values this was received on-the-wire.
`dialogue`	Dialogue Object	An object containing parameters related to the TCAP dialogue.
`components`	Array of Component Objects	An array of Objects representing TCAP components (if any are present). Not present for `type` = `ABORT`.
`abort`	Object	Information extracted from `ABORT` message received.
`p_cause`	Integer	The `reason`.`p-abortCause` if present.
`u_source`	`0` / `1`	The `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`abort-source` if present.
`u_info_0_octets`	Binary	The `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`user-information`[`0`].`encoding`.`octet-aligned` if present.
`bytes`	Binary	[Required] The TCAP-encoded bytes received on-the-wire.

TCAP-SEND

The TCAP-SEND is sent to the SigtranApp by another application wishing to place TCAP bytes on-the-wire. This message can be used to send any TCAP message type.

The attributes of the TCAP-SEND message are:

Field	Type	Description
`ack_sent`	`0` / `1`	Do we require a `TCAP-SENT` response for tracing purposes? (Default = `0`)
`type`	`BEGIN` / `CONTINUE` / `END` / `ABORT`	[Required] Specify the type of message to be constructed.
`remote_sccp`	SCCP Address Object	[Required for BEGIN] The far-end SCCP destination address to which the TCAP BEGIN is sent. This field is not used for TCAP types other than BEGIN.
`local_tid`	Hex String	[Required for CONTINUE/END/ABORT] Local transaction ID in hexadecimal format. The calling application must specify this when continuing an existing transaction. When starting a new transaction with `type` = `BEGIN` then the SigtranApp will assign a local transaction ID and provide it to the originating application by using `TCAP-CONTINUE`. Note that `remote_tid` is never specified in `TCAP-SEND`, instead it is managed by SigtranApp.
`components`	Array of Component Objects	Applicable for BEGIN/CONTINUE/END only. Not used for ABORT. An array of Objects representing TCAP components (if any are present).
`dialogue`	Dialogue Object	Applicable for BEGIN/CONTINUE/END only. Not used for ABORT. An object containing parameters related to the TCAP dialogue.
`abort`	Object	Applicable for ABORT only. Not used for BEGIN/CONTINUE/END. An object containing parameters related to the ABORT content.
`p_cause`	Integer	Applicable for ABORT only. Not used for BEGIN/CONTINUE/END. The value to encode into `reason`.`p-abortCause` if present.
`u_source`	`0` / `1`	Applicable for ABORT only. Not used for BEGIN/CONTINUE/END. The value to encode into `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`abort-source` if present.
`u_info_0_octets`	Binary	Applicable for ABORT only. Not used for BEGIN/CONTINUE/END. The value to encode into `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`user-information`[`0`].`encoding`.`octet-aligned` if present.

Note: The local SCCP address is never specified when using TCAP-SEND. It will be set automatically by the SigtranApp which performs the final message encoding and delivery.

TCAP-SENT

The TCAP-SENT is sent by the SigtranApp by another application whenever a TCAP-SEND results in a TCAP message being placed on-the-wire.

The attributes of the TCAP-SENT message are:

Field	Type	Description
`type`	`BEGIN`/`CONTINUE`/`END`/`ABORT`	[Required] The type of TCAP message that was placed on-the-wire.
`bytes`	Binary	[Required] The TCAP-encoded bytes placed on-the-wire.

TCAP-FAIL

The TCAP-FAIL is sent by the SigtranApp by another application whenever a TCAP-SEND does not successfully place a TCAP message on-the-wire.

The attributes of the TCAP-FAIL message are:

Field	Type	Description
`type`	`BEGIN`/`CONTINUE`/`END`/`ABORT`	[Required] The type of TCAP message that was not placed on-the-wire.
`local_tid`	Hex String	[Required] Local transaction ID in hexadecimal format. When this `TCAP-FAIL` is for type `BEGIN`, the sending application is responsible for capturing and storing this local transaction ID and including it when attempting to send any follow-up TCAP content for this transaction.
`bytes`	Binary	[Required] The TCAP-encoded bytes placed on-the-wire.

TCAP-PREARRANGED-END

The TCAP-PREARRANGED-END is sent by any application to the SigtranApp to indicate that the TCAP local transaction ID should be released, and that no further messages are expected to be received.

There are three ways in which a local transaction ID can be freed (and hence avoid leaking).

Receipt of an on-the-wire TCAP END or TCAP ABORT.
Sending an on-the-wire TCAP END or TCAP ABORT.
Use of TCAP-PREARRANGED-END.

The attributes of the TCAP-PREARRANGED-END message are:

Field	Type	Description
`local_tid`	Hex String	[Required] Local transaction ID in hexadecimal format.

TCAP-TRANSFER

The TCAP-SENT is used by an application which has received a TCAP-RECV containing a BEGIN message, for the purpose of redirecting/proxy of that BEGIN message to another SCCP end-point.

A TCAP-TRANSFER must be the first and only response to the original TCAP-RECV message, it is not possible to transfer a TCAP transaction after having sent a reply.

When using TCAP-TRANSFER the controlling application must specify a new SCCP end-point address, to which the SigtranApp will construct and send a new BEGIN message where:

The SCCP calling party address is identical to the original received SCCP calling party.
The SCCP called party address is set to be the new called party address.
The TCAP dialogue part is identical to the original received TCAP Dialogue (if present).
The TCAP components are those specified by the application, which should closely (or exactly) match the originals.

The TCAP-TRANSFER request will alwas be sent back to the same SigtranApp which initiated the transaction to us with the original TCAP-RECV. That SigtranApp will perform route selection for the new outbound BEGIN as if it were a brand new TCAP BEGIN. Connection affinity will not apply.

After sending the transferred BEGIN, the SigtranApp will:

a. Close the original transaction, and b. not create a new outbound transaction, and c. not expect any subsequent interaction, and d. potentially run a TCAP linger timer to catch delivery errors.

If ack_sent is set then SigtranApp will return an TCAP-SENT message to the transferring application in the same way as occurs for TCAP-SEND.

The attributes of the TCAP-TRANSFER message are:

Field	Type	Description
`type`	`TRANSFER`	[Required] Static field used as the TCAP "Type" for logging and tracing purposes.
`ack_sent`	`0` / `1`	Do we require a `TCAP-SENT` response for tracing purposes? (Default = `0`)
`remote_sccp`	SCCP Address Object	[Required] The far-end SCCP destination address to which the TCAP BEGIN is transferred. This will be the SCCP called party address.
`dialogue`	Dialogue Object	An object containing parameters related to the TCAP dialogue.
`components`	Array of Component Objects	An array of Objects representing TCAP components. The number of components, the operation codes, and invoke IDs should match the original received components. The internal component encoded parameter fields may possibly have been modified/re-encoded.

Note: The local SCCP address is never specified when using TCAP-TRANSFER. It will be set automatically by the SigtranApp to be identical to the original received SCCP calling party address (which in fact is not our local address at all, it is the remote SCCP address of the original sender).

TCAP-TXNCHECK-REQUEST

The TCAP-TXNCHECK-REQUEST is sent by the SigtranApp by another application whenever it is concerned that too long an interval has passed without any activity following the sending or receiving of a TCAP CONTINUE message.

The TCAP-TXNCHECK-REQUEST message does not have any details body.

TCAP-TXNCHECK-RESPONSE

The TCAP-TXNCHECK-RESPONSE is sent by the SigtranApp by another application whenever it is concerned that too long an interval has passed without any activity following the sending or receiving of a TCAP CONTINUE message.

The attributes of the TCAP-TXNCHECK-RESPONSE message are:

Field	Type	Description
`success`	`0`/`1`	[Required] Set to `1` iff the Instance is active, the Transaction is known, and the Transaction is open.
`error`	String	Indicates the reason for the non-success response. Present and applicable only if `success` == `0`.

Common Object Structures

SCCP Address Object

An SCCP Address Object may contain the following fields:

Field	Type	Description
`ri`	`0`/`1`	[Required] Routing Indicator. `1` = route on PC + SSN, `0` = Route on GT)
`pc`	Integer	Point Code if present.
`ssn`	Integer	Sub-System Number if present.
`gt_digits`	Hex Digits	Hex Digits for Global Title Address if present.
`gt_noa`	Integer	Global Title Nature of Address (0-127) if present. (Default = `0`)
`gt_np`	Integer	Global Title Numbering Plan (0-7) if present. (Default = `1`, E.164)
`gt_tt`	Integer	Global Title Translation Type (0-255) if present.

TCAP Dialogue Object

A TCAP Dialogue Object may contain the following fields:

Field	Type	Description
`protocol_version`	`1`	TCAP Protocol Version. Must be `1` if present.
`result`	Integer	Value for `single-ASN1-type.dialoguePDU`.`dialogueResponse`.`result` if present.
`result_diagnostic_user`	Integer	Value for `single-ASN1-type`.`dialoguePDU`.`dialogueResponse`.`result-source-diagnostic`.`dialogue-service-user` if present.
`result_diagnostic_provider`	Integer	Value for `single-ASN1-type`.`dialoguePDU`.`dialogueResponse`.`result-source-diagnostic`.`dialogue-service-provider` if present.
`application_context`	Binary	Value for `single-ASN1-type`.`dialoguePDU`.`dialogueResponse`.`application-context-name` if present.
`map_open`	Object	Attributes for the MAP-OPEN dialog section if present.
`.destination_reference_digits`	Hex String	Value for `map-open`.`destinationReference` if present.
`.origination_reference_digits`	Hex String	Value for `map-open`.`originationReference` if present.

TCAP Component Object

A Component Object may contain the following fields:

Field	Type	Description
`invoke`	Object	[Required for Invoke] Container for Invoke details.
`.invokeID`	Integer	[Required] The Invoke's ID.
`.linkedID`	Integer	Optional Linked ID iff this Invoke is associated with an earlier Invoke.
`.operationCode`	Integer	[Required] Code for the operation that this Invoke represents.
`.parameter`	Binary	Encoded binary (usually ASN.1 BER) Invoke parameter body.
`returnResultLast / returnResultNotLast`	Object	[Required for Return Result] Container for Return Result details.
`.invokeID`	Integer	[Required] The ID of the Invoke that the Return Result is associated with.
`.result`	Object	Container for result details.
`.operationCode`	Integer	[Required] Code for the result type that this Return Result represents.
`.parameter`	Binary	[Required] Encoded binary (usually ASN.1 BER) Return Result parameter body.
`returnError`	Object	[Required for Return Error] Container for Return Error details.
`.invokeID`	Integer	[Required] The ID of the Invoke that the Return Error is associated with.
`.errorCode`	Integer	[Required] Code for the error type that this Return Error represents.
`.parameter`	Binary	Encoded binary (usually ASN.1 BER) Return Error parameter body.
`reject`	Object	[Required for Reject] Container for Reject details.
`.invokeID`	Object	[Required] Container for invoke ID details.
`.derivable`	Integer	The ID of the Invoke that the Reject is associated with, if it can be determined.
`.not-derivable`	Null	Present if the Reject is not (or cannot be) associated with an Invoke.
`.problem`	Object	[Required] Container for problem details.
`.generalProblem`	Integer	Code for the problem type that this Reject represents, if it represents a general problem.
`.invokeProblem`	Integer	Code for the problem type that this Reject represents, if it represents a problem with an Invoke.
`.returnResultProblem`	Integer	Code for the problem type that this Reject represents, if it represents a problem with a Return Result.
`.returnResultError`	Integer	Code for the problem type that this Reject represents, if it represents a problem with a Return Error.