In an earlier paper we showed, that perceived quality of channel zapping is related to the perceived quality of download time of web browsing, as suggested by ITU-T Rec.G.1030. We showed this by performing subjective tests resulting in an excellent fit with a 0.99 correlation. This was what we call a lean forward experiment and gave the rule of thumb result that the zapping time must be less than 0.43 sec to be good ( > 3.5 on the MOS scale). To validate the model we have done new subjective experiments. These experiments included lean backwards zapping i.e. sitting in a sofa with a remote control. The subjects are more forgiving in this case and the requirement could be relaxed to 0.67 sec. We also conducted subjective experiments where the zapping times are varying. We found that the MOS rating decreases if zapping delay times are varying. In our experiments we assumed uniformly distributed delays, where the variance cannot be larger than the mean delay. We found that in order to obtain a MOS rating of at least 3.5, that the maximum allowed variance, and thus also the maximum allowed mean zapping delay, is 0.46 sec.

The end user experience of service quality is critical to the success of a service provider's IPTV deployment program. A key element involved in validating IPTV quality of experience (QoE) is how qiuckly and reliably users can change TV channels, often referred to as channel zapping. Currently there is no knowledge about the explicit relation between zapping time and the user perceived quality as expressed as a Mean Opinion Score (MOS). We have proposed a model where the MOS depends on the zapping time on a logarithmic scale. In order to validate our model we have conducted a number of subjective tests in order to get insight in this relation. The tests were performed by 21 test subjects at TNO and at Acreo. It turns out that the correlation between the subjective data and the perceptive model is very high (0.99). Therefore we conlcude that our perceptive model is very useful for assesing the perceived quality of zapping. The result is not limited to IPTV but applies to any type of TV service with channel switching times that are not instantaneous, regardless whether it is terrestial or satellite based.