VoIP - Pt. 3 - Packet Loss

In monitoring VoIP traffic there are critical metrics and issues to understand which will improve your ability to quickly troubleshoot performance and call quality issues. In the last article we covered the impact that jitter and delay can have upon VoIP applications. Today, we’ll be covering the issue of packet loss and how to identify it within a within a VoIP call.

Understanding Packet Loss
Packet loss is an important factor to monitor in a VoIP call. Networks tend to either sporadically drop single packets (these periods are called “gaps”) or large numbers of contiguous packets in a “burst.” Packet loss concealment techniques typically mask the impact of packet loss during gap periods. Bursts, however, can overwhelm the packet buffer causing packet loss, or result in a delay if packet delivery fails. Bursts can be caused by network congestion, media failure, or link failure.

With bursts it is important to monitor for burst percentage. This is the percent of time that bursts are occurring relative to the call. Another factor is burst density, which measures the average percent of missing packets in a burst. In addition to burst metrics, gaps are just as important to understand. Gaps occur between bursts, and locating a gap helps the administrator define the burst. Important metrics for gaps are gap density, the percent of packet loss during the gap, and average gap duration, which is the length of the gap measured over time.

[Stephen Brown and Charles Thompson of Network Instruments]

[tags]voip,delay,site survey,benchmark,network performance,voip metric,cdr,call detail record,packet loss[/tags]