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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-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. See below.
`local_sccp`	SCCP Address Object	[BEGIN, Required] Our local SCCP address. See below.
`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_information`	Array of Binary	The raw ASN.1 content for any elements in the `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`user-information` if present.
`bytes`	Binary	[Required] The TCAP-encoded bytes received on-the-wire.

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_digit`	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.

A 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.

A Component Object may contain the following fields:

Field	Type	Description
`type`	`Invoke`/`ReturnResult`/ `ReturnError`	[Required] Indicates type of component contained within.
`last`	`0`/`1`	Applicable only for `type` = `ReturnResult`. (Default = `0`)
`invoke_id`	Integer	[Required] The Invoke ID for this component for all types.
`invoke`	Object	[Required for Invoke] Parameters within the Invoke.
`.linked_id`	Integer	Optional Linked ID iff this Invoke is associated with an earlier Invoke.
`.parameter`	Binary	Encoded binary (usually ASN.1 BER) Invoke parameter body.
`result`	Object	[Required for ReturnResult] Parameters within the ReturnResult.
`.operation_code`	Integer	Operation Code for which this result applies.
`.parameter`	Binary	Encoded binary (usually ASN.1 BER) ReturnResult parameter body.
`error_code`	Integer	[Required for ReturnError] The code describing the error.

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] The far-end SCCP address.
`local_sccp`	SCCP Address Object	[Required] Our local SCCP address.
`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_information`	Array of Binary	Applicable for ABORT only. Not used for BEGIN/CONTINUE/END. The elements to encode into `reason`.`u-abortCause`.`single-ASN1-type`.`dialoguePDU`.`dialogueAbort`.`user-information` if present.

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-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-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`.