Layer 3 Call Tracing Service
We designed a high level diagnostic facility for incorporation into a number of Teltrend products.
The Call Tracing service was designed to provide a generic mechanism for on-line diagnostic tracing whereby call interactions could be retrieved at various levels of detail, with a guarantee of long-term data retention for “hung” calls, even under high overall traffic loads. It was intended to be used primarily by support personnel in the event of the customer reporting problems with calls not completing satisfactorily. It could be operated remotely, or locally via a connected management terminal.
The call tracing software was designed so that it could be added to existing protocol stacks with minor alterations. Provision was made to handle a variety of stack types: those controlling a single ISDN interface as well as those controlling multiple interfaces. Voice, data and virtual calls were supported.
The layer 3 tasks passed information to the call tracing subsystem upon the transmission or reception of messages to / from the line. The data was stored in a circular log, with each message annotated so that the layer 3 events could be retrieved, if still stored, by line, channel, call type, time period, called / calling party number or other criteria.
The call tracing service was controlled by a PC-based external management system. This allowed the operator full control over which calls were stored in the log and which messages were retrieved for examination. Remote operation was possible via a modem.
The task was designed to run on the Teltrend proprietary multi-tasking operating system. The design process required detailed knowledge of the existing product software architecture. It was coded mainly in C, but with some Pascal elements so that it could interface to other software subsystems written in Pascal.
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