XConnect's network touches the Internet at dozens of points around the globe, giving Schwartz unique insight into real-world traffic conditions. And while packet loss rates might be better in more industrialized countries, infrastructure demands are also higher, heightening the effect of packet loss.
"With the ever-increasing set of applications engaging in real-time audio and video communications, we can expect network based packet loss to be a critical factor in the future growth of this industry." What's more, packet loss statistics like these, and particularly the ones cited by carriers, can be enormously suspect. Many service providers only cite statistics for their carefully managed backbones, not for the last mile, where loss is likely to be greatest.
Even when packet loss statistics are measured, they're averaged over a month or even a year, diluting the true impact of a single event on a user's experience. In other words, they measure average loss without accounting for the damaging effects of peak loss. "The fine print on the 5 percent packet loss is that if the loss is randomly distributed, 5 percent is no big deal. But, typically, loss is not randomly distributed. Often you lose a clump of packets. So if you lose three packets in a row, voice can sound like crap even though it is less than 5 percent packet loss," he says.
Dave Taht agrees. "You want to avoid bursty packet loss. Losing five packets in a row results in a major dropout. Most codecs can compensate for three OK, and two fairly well, but it is codec- dependent." Taht is the CEO of Teklibre, a research and development organization advocating for Internet development within the Third World. Taht developed one of the first embedded, Linux-based wireless routers.
There's also the problem of variance in packet loss. "If most of your packets are taking 60 to 75ms to reach the other end, and suddenly one packet takes 140ms, that packet arrives so late that is close to the same as lost from a voice-quality point of view." And this is on voice. Video we know is far more suspect. "We've seen video degradation at .25 percent packet loss," says Damon Ennis, VP of product management at Silver Peak Systems.
