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Skype and Network Latency
Authored by: billclinton on May 22, '06 04:00:34PM

I tried Skype about a year ago and found it to be quite poor. The main problem is network latency--it was impossible to have anything like an ordinary conversation, and that was when calling my buddy across town (via Skype Out). I don't know if there is additional latency when using Skype Out as compared to communicating computer-to-computer, but my guess is that if there is, that it is quite small. Later, I called the same friend from Spain. This was a truly awful experience, as the latency was probably between 500 ms and 1 s.

Cell phone latency is also quite poor, and I don't know why more people don't complain about it. But Skype (Out), in my limited experience, is usable only in dire circumstances.

Symptoms of excess latency are "two-way stutter," when one speaker starts to talk, perceives that the other person has butted in and stops. In the meantime, the first speaker's voice has reached the second speaker, and the second speaker perceives that the first speaker has cut _him_ off. This continues until one speaker says "screw this, I'm going to talk no matter what." Sometimes, the second speaker makes the same decision at around the same time, and both speakers end up talking simultaneously, each thinking that the other is a butthole for rudely interrupting.

In the language of control systems engineering, this is a feedback loop with excessive delay. As all control systems engineers know, a feedback loop with too much delay (here, network latency), becomes unstable and oscillates. With cell phones and worse with Skype, this is manifested as the "two-way stutter" phenomenon.

Human conversation takes place on a much finer time scale than most people appreciate. Even a small latency messes up the normal give-and-take of ordinary conversation. Only in formalized settings such as (I would imagine) lawyers talking to one another (where one usually doesn't interrupt the other because one is waiting for the other to say something stupid anyway) is a bit of latency acceptable. I recently talked to a friend who said that he (a former ham radio operator) had to "train"his girlfriend to talk on a cell phone by actually making a "czzzzkkkkk" sound like that of a microphone disconnecting.

I'm and engineer and I work with audio frequently (but don't call me an audio engineer, please 8^). "Non-audio" people frequently say they experienced "good sound" or "bad sound" or the like but don't specify what aspect or aspects of the sound was good or bad, probably because they lack the vocabulary or the experience to notice that, say, the distortion was low and there were a few dropouts, but there was a strange echo or the SNR was low or there was too much latency.

Anyway, I'm just wondering what others think of the latency on Skype, and how it varies with network loading.



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Skype and Network Latency
Authored by: chyna4xena on May 23, '06 11:05:36PM

If you are getting latency on SkypeOut, I wouldn't just assume there'd be similar latency on Skype-to-Skype calls - the interface between the Skype network and the POTS seems to me to be a likely candidate for a bottleneck.

As others have noted, latency on Skype-to-Skype calls is rare, and when it exists, is not dramatic. I have rarely experienced a detectable hint of latency, and I'm on only a 512/128 connection (I haven't Skyped internationally, though). It was always temporary; as soon as the overtaxed CPU relaxed, the latency disappeared.



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