The Answer-Seizure Ratio (ASR) is calculated by dividing the number of successfully answered calls by the total number of calls attempted, which are known as "seizures". Since busy signals and other rejections by the called number count as call failures, the calculated ASR value can vary depending on user behavior.
60-70% is considered a very good ASR in the VoIP world.
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 Qoschanges. 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 Tone, is sometimes also referred to as Post Dialed Delay. For a well dimensioned network this figure of merit should be 150 ms or less.