So what's the catch? Why isn't multicast deployed ubiquitously across the Internet? Unfortunately, multicast requires a rather complex set of protocols that determine where the interested receivers are and replicating traffic only to those end users.
In the late 1990s, there was much hope and hype surrounding multicast over the Internet. It was predicted that every dorm room could become a TV or radio station and audio/video streams would be as numerous as Web sites. Multicast advocates focused on "encouraging" service providers to deploy the protocols necessary to support multicast on their networks. Several very large service providers, such as Sprint and Level 3, deployed multicast on their Internet backbones. And on research and education networks, like Internet2, multicast became a crucial service offering. However, for various reasons, multicast deployment on downstream networks was sporadic and in most cases non-existent.
The biggest problem multicast presented was an "all or nothing" solution. Every link on the network, every router and firewall between source and receiver, required multicast protocols to be enabled. Additionally, the business model for multicast is abstract and is not an easy case to make. Multicast is an infrastructure capability that enables other services. From a business perspective, multicast resembles DNS and BGP, which are vital infrastructure protocols that are generally not billed directly. Consequently, those service providers who tried to bill for Internet multicast found disappointing results. Content providers were not interested in paying extra to transmit multicast streams that couldn't be received by many end users, and networks with many end users were unwilling to pay extra to receive multicast content that didn't exist. The result was a chicken-and-egg problem between content and audience.
It should be noted that multicast has enjoyed success in certain places. On financial networks, multicast is a vital service as applications such as stock quote data is delivered from one central market location to thousands of traders simultaneously. On some enterprise networks, multicast is equally indispensible as it is used for such purposes as transferring price lists from a central headquarters locations to thousands of local retail stores.