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 internal (i.e. undocumented) ScriptApp testing utility, and the official applications such as DsgScpApp, NpScpApp and AcdScpApp (et al.) which are subclasses of the ScpApp utility class.

The SigtranApp maintains and manages a single pool of correlation IDs across the entire n2svcd instance 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 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:

• CORRELATION-ID-REQUEST
• CORRELATION-ID-RESPONSE

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”.