This report examines the issues that may occur as the number of IP TV networks become very large, and as single IP TV networks exceed one million subscribers. It identifies potential bottlenecks and describes strategies for avoiding them.Elements of an IP TV Network
Large IP TV (often called ?IPTV?) networks are typically organized into a hierarchical architecture that includes:

• A super video headend that acquires the national broadcast channels and the video on demand (VOD) content.
• Regional headends that acquire local channels and include the VOD servers.
• The access network that includes ADSL and VDSL DSLAMs, or the systems that provide fiber services to the individual subscribers.
• An IP/MPLS network that carries the encoded national broadcast channels and the video on demand content to the regional video headends.
• An Ethernet aggregation network that carries the broadcast content from the regional video headends to the access network that distributes it to the subscribers.
• Software systems that include the middleware that manages the IP TV service, the content protection/digital rights management (DRM) systems that protect IP TV systems, along with the back office systems that are used to manage and provision the IP TV network.
  

Size of IP TV Networks
The database used to create MRG?s Market Leader Report published in August 2005 identifies five service providers that have more than 100 thousand IP TV subscribers today. Three of these service providers have less than 200 thousand subscribers and the largest has over 650 thousand. From this, it is clear that nearly all service providers are just beginning to address scaling issues.

This situation is likely to change significantly over the next several years. The model used for MRG?s IP TV Global Forecast 2005 ? 2009, published in September 2005 indicates that at end of 2009, 40 service providers are likely to have over 100 thousand subscribers, and that eight of these service providers will have more than one million subscribers. The largest deployment identified in the forecast is expected to have three million subscribers at that time. It is clear that many service providers will be addressing significant IP TV scaling issues over the next few years.


Factors Affecting IP TV Scaling
There are a number of factors that will influence the scaling of IP TV networks:

• The number of IP TV subscribers is the overriding factor, and is the basis for most of the other factors.
• The number of IP TV subscribers using VOD services.
• Channel change behavior for broadcast services.
• Use of services that generate transactions such as use of TV-based Internet portals, or video-based e-mail or commerce portals.
• Use of games and other interactive content.
• Viewing of High Definition TV (HDTV) content.
• Depth of the electronic program guide (EPG).
• Dependence of middleware on network services.
• The distribution of VOD servers in the network.

Bandwidth Requirements in IP TV Networks
Table 1 lists the bandwidth requirements for IP TV at the service level, in the access network, and in the aggregation network. This table shows that a minimum of 20 Mbps is required for an IP TV service with HD content. It also shows that this 20 Mbps or more of bandwidth should be carried through the access and aggregation networks, except that there can be some reduction in the aggregation network due to the statistical nature of best-effort Internet traffic.

Table 1: Bandwidth Requirements in a Triple-Play Network

Service	Service Bandwidth	Access Network Bandwidth	Aggregation Network Bandwidth
Video (3 SD 1 HD)	14 Mbps	14 Mbps	14 Mbps
VoIP (3 phones)	200 Kbps	200 Kbps	200 Kbps
Internet	5 Mbps	5 Mbps	200 Kbps
Total	20 Mbps	20 Mbps	15 Mbps

Source: MRG, Inc.