IP TV

S ervice providers are continually increasing the number of TV chan-nels they offer their subscribers. Despite digital video recorders ’ wide-spread use, the consumption of linear TV content has continued to increase as more channels become available. Re-cent data collected from a major cable TV deployment in the US show that viewers change channels on average 25 times a day. The data also show that some viewers change the channel al-most every minute and others several times a minute during peak channel-change times, such as at the top of the hour. As channel line-ups get richer, we could very well observe increasing channel-change frequencies. In conventional analog broadcast, TV tuners can complete a channel change in a single frame time and ren-der the next frame of the new chan-nel immediately. Thus, viewers usually feel as though zapping, or channel-change, times are virtually instant. Because conventional analog television is a broadcast medium, zapping times don’t vary, no matter how many view-ers change channels at the same time. In digital cable and satellite broad-cast, the zapping demand — that is the aggregated number of channel-change requests — doesn’t have an impact on zapping times, either. However, com-pared to its analog counterpart, digi-tal broadcast does have longer zapping times due to compression and encryp-tion applied to the content. In a multicast IPTV distribution network, each channel is offered in a different multicast session, and the IP set-top box joins the respective session when the viewer tunes to a new channel. Due to delays associated with network components and encoding schemes, the time difference between the channel-change request and when the new channel shows up on the screen can be annoyingly large. This article examines the Real-Time Transport Protocol (RTP) in IPTV networks and describes how RTP and its control protocol can help reduce channel-change times