IP TV Bandwidth Demand: Multicast and Channel Surfing

Authors: Donald E. Smith

Complete Citation

• Donald E. Smith. IP TV Bandwidth Demand: Multicast and Channel Surfing. INFCOM.2007, p.2546-2550

Abstract

IP networks may soon become a delivery mechanism for broadcast television content. Multicast can reduce the steady state bandwidth demand on network links from one stream per viewer to one stream per watched program. However, channel surfing at commercial breaks can periodically increase the bandwidth demand. In the channel change mechanism we study, surfers leave multicast groups and receive unicast streams at higher than usual bandwidth. This paper builds a mathematical model to determine the net bandwidth demand of multicast and surfing during commercial breaks. In one example, we find that the peak demand during a commercial break is twice the steady state multicast demand.

Annotations

The paper developed a model that quantifies the bandwidth demanded by IP TV viewers when they surf at commercial breaks.

• fiber-to-the-premises model:
  An Optical Line Terminal (OLT) forwards the content over a Passive Optical Network (PON) to the Optical Network Terminal (ONT) at each subscriber's premise. The PON typically serves up to 32 subscribers while the OLT serves roughly 2000 subscribers.

• Demand assumption and multicast model:
  

Demand follows Zipf's law meaning that viewers are twice as likely to watch the most popular program than to watch the second most popular program, three times as likely to watch the most popular program than the third most popular program, and so on.

The multicast model predicts the steady state bandwidth demand from a population of m viewers watching broadcast streams over IPTV. For example, it turns out that 400 viewers will watch an average of only 154 different broadcast channels with demand following Zipf's law.

• Channel surfing model:
  

Describes how a viewer makes multiple channel changes during a commercial break. The paper assumes this behavior follows a terminating renewal process.

• Results of bandwidth demand:
  

The multicast demand increases as time progresses and surfers quit surfing and settle down into multicast groups. The Surfing curve decreases as viewers stop surfing. The mean total bandwidth decays asymptotically to about 1000 Mbps as a result of multicast savings. However, the maximum demand in this figure reaches almost to 1700 Mbps, which means channel surfing gives back nearly all multicast’s gains.

-- YingxinJiang - 18 Jul 2007