One of the big questions on the minds of VoIP administrators is how can you effectively monitor calls so that you know when the system is performing above or below user expectations. Naturally, most network vendors offer expensive management solutions with claims of comprehensive call monitoring, but a lot of administrators opt for much simpler and cheaper solutions where they monitor only a single factor like latency, and sometimes they figure an easy way to monitor jitter as well.
If you're looking for a monitoring solution for your voice network, you should consider implementing the EIF monitoring. If you've already got a network management system in place that is capable of accepting SNMP traps, this functionality should come at no additional cost.
EIF, which stands for Equipment Impairment Factor (Read ITU Recommendation G.113 for detailed information), contains a composite metric that includes circuit noise, volume, quantization distortion, echo, delay and more. The DSPs that convert your analog voice to digital packets give all this info to the router that then send an SNMP trap when the metric exceeds a threshold you configure.
In a Cisco IOS router, EIF is configured at a dial-peer level using the "expect-factor" and "icpif" keywords. The value for expect-factor ranges from 0 to 20, where 0 means that the users expect toll-quality voice, and 20 means that the users are very tolerant of poor quality voice, much like cell phone users or international callers. The "ipcif" value, which ranges from 0 to 55, equals Itot, which is the info supplied from the DSP, minus the expect-factor.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.