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CORRELATION-ID Messages

Introduction

The CORRELATION-ID-… messages are used by “SCP-style” applications to request SigtranApp to assign a temporary Correlation ID for the purposes of correlating an INAP/CAP AssistRequestInstructions back to the associated call instance.

These “SCP-style” applications include the LhoScpApp which allows Lua scripts to perform CAMEL/INAP control of InitialDP voice calls and InitialDPSMS short message control as used by the N2ACD (CAMEL/INAP mode) and N2IWF (CAMEL/INAP mode) products.

Also, the TcapLuaService provides freeform Lua control of inbound CAMEL/INAP calls, and provides access to correlation IDs via this mechanism.

The SigtranApp maintains and manages a single pool of correlation IDs which is available to all of the separate SCP services (typically including multiple repeated instances of the same SCP service for performance reasons).

Any SCP application (or Lua service) may send a CORRELATION-ID-REQUEST to the ScpApp to request the assignment of the Correlation ID when they wish to send out an INAP/CAP EstablishTemporaryConnection operation to the SSP/MSC.

The SSP passes this Correlation ID to the Specialized Resource Function (SRF) which includes it in the AssistRequestInstructions operation which returns back to the SCP as shown in the following life-cycle diagram:

This round-trip of assignment request, response, ETC, and ARI typically takes place within one second, and in any case must take place within the configured maximum lifetime of the correlation ID within SigtranApp (defaults is 10 seconds).

After that time, if a AssistRequestInstructions for the Correlation ID has not been received by SigtranApp, the Correlation ID is considered to be expired. It will be returned to the pool and an warning alarm will be raised.

The CORRELATION-ID-… messages are:

Context for CORRELATION-ID Messages

Note that when using send_message to send CORRELATION-ID-… 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
CORRELATION-ID-REQUEST
Other App -> SigtranApp 		"|"
For the future associated transaction. 		Existing Local TID
Assigned by SigtranApp
CORRELATION-ID-RESPONSE
SigtranApp -> Other App 		"|"
For the future associated transaction. 		Existing Local TID
Assigned by SigtranApp

CORRELATION-ID-REQUEST

The CORRELATION-ID-REQUEST message is sent to SigtranApp by any application that wishes to be assigned a Correlation ID for the purpose of ETC/ARI correlation through that SigtranApp.

Refer to the SigtranApp Configuration documentation for more information on configuring the Correlation ID pool including Correlation ID length, pool size, pool boundaries, and Correlation ID lifetime.

The CORRELATION-ID-REQUEST message has no message details.

CORRELATION-ID-RESPONSE

The CORRELATION-ID-RESPONSE message is sent by SigtranApp to the requesting application to provide the newly assigned Correlation ID.

The attributes of the CORRELATION-ID-RESPONSE message are:

Field Type Description
success 0/1 [Required] Indicates if the request was successful or not.
error String Indicates the reason why the request failed.
Present and applicable only if success == 0.
correlation_id Digit String The assigned correlation ID as a string being [0-9] digits only, padded with leading 0 as necessary to reach the configured correlation ID length.