The time between pushing the channel change button and the first video frame being displayed on the TV, is called zapping delay. Besides the acceptable audiovisual quality, channel zapping delay is a fundamental requirement for quality of user’s experience (QoE). Although it seems to be a natural requirement from a subscriber's perspective, assuring this functionality can be problematic for IPTV service providers. In this chapter, the various elements that influence zapping delay are discussed and then, accordingly, efforts to reduce this delay are presented. Thereafter, pre-joining method is proposed for OFDMA-based wireless networks such as WiMAX.
