While monitoring all calls in a VoIP network can be an invaluable tool, other service metrics should be used as well to measure quality performance. Service-centric metrics based on signaling analysis have proven to be invaluable to high quality voice services. Tracking performance metrics should be done with a fine granularity. For example, it is recommended that a sampling rate of no more than 5 minutes should be used to catch QoS changes. Some typical performance metric definitions are as follows:
ABR: Answer to Bid Ratio - Answered Calls divided by Attempted Calls in a given time period.
ASR: Answer to Seizure Ratio - Answered Calls divided by voice circuits successfully captured.
CSR: Call Success Ratio - successful call signals divided by attempted call signals; provides a good determination for how well network signaling is working.
CST: Call Setup Time - Defined as: time from last dialed digit to reception of “Ringing Toneâ€, is sometimes also referred to as Post Dialed Delay. For a well dimensioned network this figure of merit should be 150 ms or less.
NER: Network Efficiency Ratio - Defined as: ASR/ABR and thus taking the user behavior out of the equation. It gives the percentage of successful allocation of a voice circuit i.e. an indicator of congestion in the network. Should be very close to 100%.
