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Multicast is the term for packets of data sent not to a single destination (that would be unicast) but rather to a class of devices. It is a bandwidth-saving technique associated with classic IPTV. But is it relevant for Pay TV operators looking to migrate to an over-the-top (OTT) delivery of linear video?
The answer is maybe, maybe not. Network capacity is limited and certain multicast technologies are intriguing, but consumers are simply trending away from the scenario—many people watching the same content—optimized for multicast. Meanwhile, unicast supports popular multi-screen and on-demand viewing behavior and can potentially support its monetization, an increasingly urgent task.
“If I can leave the connection between end user and edge box as pristine and unique as I possibly can, that’s more valuable for an ad insertion or subscription-based model than just a multicast spray and pray,” said Michael Fay, Senior Director, CDN Product Management, for Level 3. “Depending upon how smart your CDN is, that relationship between edge server and end user is probably the most important thing in content delivery right now.”
Fay said that some of Level 3’s routers are enabled multicast delivery, but that for a global CDN, multicast has few advantages. The argument might be more compelling, for a regionally concentrated pay TV operator, such as New York-based Cablevision, he suggested. In that case, the inefficiencies of making content ubiquitous become irrelevant because ubiquity is what the operator wants.
Router configuration is a gating factor. “The biggest blocker to folks doing multicast these days is having a multicast-router enabled network,” said Chris Knowlton, VP Product Management for Wowza, a media server and video streaming software provider. “Very few public networks have multicast enablement.”
Knowlton said an exception to that rule was a widespread deployment of multicast in the UK promoted by the BCC several years ago in response to bandwidth constraints. But last year’s notice by BT that is would deploy multicast routers was something else. It was linked to its planned rollout of (classic) IPTV. Multicast is key to Internet Group Management Protocol (IGMP), the basis for most IPTV systems.
Multicast thus continues to play well in private networks, or walled garden scenarios. “The biggest use case is the enterprise, where you may have 100,000 users, and maybe 50,000 on a single network in a large headquarters somewhere,” Knowlton said. “It doesn’t make sense to send out 50,000 1 MB unicast streams and bring down the whole network.”
In its recently released Wowza Media Server 3.5, the streaming technology company included support for Silverlight Multicast Player. That integration enables enterprises to use Wowza and move to adaptive bit-rate (ABR) streaming capabilities in house, while continuing to use the familiar player. Knowlton said that Microsoft has not produced a Windows Media Server that can provide ABR multicast, but that a Silverlight feature allowing for video to be imported in a raw format enabled this implementation.
As for helping Pay TV operators migrate to OTT transport of linear content, Knowlton said multicast could “play a part in that, as far as delivering content to edge points, to headends or central offices, where content then needs to split off and go to the individual subscriber level, using unicast with HTTP.”