Wednesday, March 26, 2014

Under Correlation & Over Correlation in Your Voice Monitoring System

One of the big contributions of a Voice Monitoring System to reducing costs in voice operations is the ability to bring all legs of a VoIP call from all segments or even geographical parts of your network together in one message flow or ladder diagram.

Sometimes the process is not perfect. Most commonly seen is under correlation.This is where some of the legs of the calls are not correlated together. In some monitoring systems the user can see multiple instances of the same call. In other monitoring systems, it is not evident and pieces remain missing.

When a SIP call passes through an SBC (Session Border Controller) implementing theBack-To-Back User Agent [B2BUA] functionality, the call ID will be changed. This usually presents a problem to monitoring systems attempting to correlate the two legs of the call together. However the caller or called part of the User Agent i.e. the phone number may remain the same or at least some part thereof. The format of the caller or called number may change in which case the correlation function needs to use only the common digits, which weakens the process.

Alternatively, the SDP session ID may remain the same and be used for correlation.

Correlating the same value in a given field is time sensitive. Such values rotate and need to be reused. In addition, calling and called numbers maybe redialed, causing separate calls. So the call merging function needs to look only within a given time interval, to avoid pulling pieces of different calls into the same call record or ladder diagram.

Sometimes all values are uniquely generated by a network element. This leaves no common values to search for relating to the same call.

Fortunately, Palladion, now known as Oracle Communications Operations Monitor (OCOM) is a little different from other voice monitoring systems. it has a totally customizable Call Merging Algorithm or correlation function which is user scriptable or configurable. This means regardless of how your network is setup or how your network elements treat the SIP signaling protocol packets, Palladion can always find some common information in the different legs of the SIP call to pull it altogether.

Sometimes over correlation is seen. This occurs when legs or segments from different calls are correlated into the same call record. This may be because the parameters on which correlation is achieved are identical between different calls over the time correlation interval.

However, now with some fine-tuning or a bit of scripting, we can ensure 100% accurate call correlation. This means that instead of taking an hour or two to troubleshoot a complex problem involving a trace, with Palladion/OCOM, it takes you 1-2 minutes.

If you need help with such optimization, please do contact us!
Richard Jobson, Teraquant Corporation

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