DENVER -- Cable Next-Gen Broadband Strategies -- Docsis 3.0 gives MSOs the ability to offer premium tiers that provide speed bursts north of 100 Mbit/s, but few U.S. consumers have signed up for speedy-but-expensive wideband service packages.

Time Warner Cable Inc. (NYSE: TWC), for example, added just 5,000 D3 customers in the fourth quarter of 2010, versus 147,000 customers for its non-D3 "Turbo" tier.

And that might be just fine and dandy for TW Cable and other cable operators, considering what they probably really have in mind for D3, anyway. Rather than using Docsis 3.0 primarily as a high-end tier and a weapon to wield against fiber-to-the-home competition, it's becoming abundantly clear that the longer-term vision for wideband is to have it serve as a high-capacity pipe for the transition to IP video.

To see that vision in action, one just has to take a look at some of the new hybrid gateways and set-tops that are expected to come on line in growing numbers this year. The vast majority of them will have embedded D3 modems that can serve as conduits for IP-based video services.

And that sort of thinking continues to weave itself into the Docsis 3.0 specs themselves, as CableLabs Director of Docsis Specifications Matt Schmitt shared here last week.

CableLabs, he said, has been working on ways to improve how IP multicast works in the D3 environment. In that scenario, much like it works today with cable switched digital video (SDV), an operator can send out one stream that can be received by multiple destinations.

While unicast is a tool for on-demand video, IP multicast could help MSOs conserve how much bandwidth they use up for linear IP video. So, if a customer on a particular service group, for example, tunes to a channel on the MSO's linear IP video lineup, the operator creates that multicast stream. If any other customers in that group also tune into it, they simply merge with that stream, eliminating the need for the operator to set up a separate one.

Schmitt said CableLabs has redesigned that capability in D3 by moving control from the modem to the network and the cable modem termination system (CMTS). CableLabs has also introduced two more features: multicast QoS and multicast authorization/encryption.

Multicast QoS adds service flows for D3 IP multicast traffic. But there are three types.

The first would apply QoS to a specific stream of packets from one source to one destination multicast group, which might come in handy for guaranteed premium video services. The second would apply to multiple multicast streams, which could include a use case in which an operator has an agreement with a third-party provider that gives it access to a certain level of QoS. The third example is a "default" group service flow that could limit the amount of bandwidth that's allocated for unmanaged multicast traffic, there to ensure that such traffic can't overwhelm the network.

Tied into that, the authorization piece is there to make sure that the modem is allowed to access and decrypt a specific multicast IP stream.

Although these capabilities are being added to D3, if or when MSOs actually take advantage of those new features is another story since deployment and usage scenarios will be up to the MSOs themselves, Schmitt stressed.

For more information on Docsis 3: