The initial service is designed to support broadcast of streamed IPTV content but NBN Co says it will be developed to support one to many distribution of content such as software updates and educational materials.
Service providers can already deliver IPTV content over the NBN via unicast - where each end user receives a separate data stream - and, according to NBN Co's head of product development and sales, Jim Hassell, multicast would become more cost effective where a service provider had more than about 170 customers served from an NBN point of interconnect.
"I think the big thing with multicast is that it will enable retail service providers to offer the triple play of broadband, telephony and video," Hassell said. "That's what has happened in the US."
There are three components of the multicast service, in addition to the basic fibre access. Providers must buy a multicast virtual access circuit for each customer served. This is charged at $2 per month for the first 5Mbps of bandwidth, $5 for 20Mbps and $5 for each additional 10Mbps up to a maximum of 50Mbps.
"You might have two TVs in a home with people watching differing programs in high definition and recording another two programs. He also pointed to the expected availability on Australia within a year of '4k' HDTVs. Offering higher resolution than today's TV but requiring much greater bandwidth to achieve this.
In addition to the multicast access virtual circuit, providers also require a multicast domain charged at $2.50 per Mbps for a minimum of 100Mbps with increments of 100Mbps up to a maximum of 1000Mbps. The multicast domain must be large enough to accommodate the total bandwidth of content delivered by the provider to a point of interconnect.
The service provider must also specify a media stream of sufficient capacity for each service delivered, with a minimum of 2.5Mbps. The fee for this is waived for the first 200 streams per customer and charged at $50 for each additional media stream.
Hassell said he expected the first multicast services to be offered to consumers about eight weeks from launch.