Synthetic monitoring: definition and a practical example
Short answer: Synthetic monitoring, or synthetic call monitoring, is testing in which a system places real calls on a schedule to a number or circuit and records whether the call connected, what answered and how the audio sounded.
In Portuguese: Monitoramento sintético
What is synthetic monitoring?
Synthetic monitoring means monitoring a service by doing what a user would do, instead of waiting for a user to show up. In telephony these are synthetic calls: real test calls, placed by a system on a schedule, to a toll-free (0800) number, an IVR or a SIP trunk. Each call records whether it connected, who answered, whether audio flowed both ways and what the quality was.
The adjective comes from website and network monitoring, where a test simulates a user’s visit. Among people who run voice networks, the more common name is active monitoring. Both describe the same idea, and both stand opposite passive monitoring, which analyzes the calls customers have already made, through SIP and RTP capture or call detail records.
Synthetic or passive
| Question | Passive | Synthetic |
|---|---|---|
| Analyzes real customer calls | Yes | No: it places its own calls |
| Sees the 0800 that nobody called overnight | No, it only sees what passes | Yes, the test call dials |
| Measures the quality of the received audio | Through the network, usually estimated | From the audio of each test call |
| Shows whose fault a failure is | Depends on what was captured | Brings the route’s answer on every call |
One does not replace the other. Passive shows what customers experienced; synthetic shows what a customer would experience right now, even when nobody called.
In practice
A circuit is tested every 15 minutes, for example. At 3:10 a.m. the carrier route stops completing calls. With passive monitoring, nothing shows until someone calls, and in the middle of the night that can be late. With synthetic monitoring, the 3:15 call fails and is retried, and four consecutive failed calls open an incident with the SIP code received, before the first customer complains.
How Monitor uses this
Monitor is a synthetic monitoring service: 2N5 calls each voice circuit at the agreed pace, checks the response, the audio and the message, retries a failed call, and only then opens the incident. See the guide to synthetic call monitoring and SIP trunk and VoIP monitoring for how it works.
Frequently asked questions
Is synthetic monitoring the same as active monitoring?
In telephony, in practice, yes. Both names describe tests that the monitoring itself starts, as opposed to passive monitoring, which only observes the calls customers have already made. Synthetic is the term inherited from website and network monitoring; active is the one voice engineers use more often.
Does a synthetic call count as a real call?
Yes, in the sense that matters: it crosses the carrier, the route and the answering point like a customer call, so it finds failures the equipment cannot see. What makes it synthetic is only who starts it, a system, and the script, which is always the same, so each call can be compared with the one before.