October 8, 2007

TWC Deploys BusinessLink.tv: Multicast over DOCSIS

By Carl Weinshenck

BusinessLink.tv is the first instance of real time encoding of data and its delivery via multicasting over DOCSIS. That’s according to Bhupender Kaul, vice president of commercial services for Time Warner Cable of New York and New Jersey.

A key design requirement for the 10-channel, business-programming package, which has been in beta tests for several years, was a centralized architecture that minimizes bandwidth needs on the corporate LAN.

Equipment placement also was an important issue for planners for a couple of reasons: The operator didn’t want encoding gear at the edge — which would lead to subsequent scaling issues — and was reluctant for a plan that added customer premise gear to user desktops, which generally are cluttered.

Multicast Approach

Multicast over DOCSIS answered these challenges. In multicast, a single transmission of requested information is replicated at nodes only as other requests for it are received from deeper in the network. Multiple branches of data (television programming, in this case) propagate off each node in order to satisfy those requests. The use of DOCSIS enables cable modems to do the heavy lifting at the subscriber's desk.

The benefit is that the programming is sent only to those who request it. In broadcast scenarios bandwidth is wasted by sending programming to all subscribers — who then choose whether or not to use the data.

"The benefit we bring is that without the loss of quality…we have end user savings as well as savings at the core," Kaul says.

BusinessLink.tv, which is available in parts of New York City, upstate New York and New Jersey, requires 4 Mbps of a company's local-area network (LAN) capacity.

DOCSIS 1.1 vs. 3.0

BusinessLink.tv relies deeply on the marriage of multicasting and DOCSIS. The industry, through CableLabs, is meshing the two. DOCSIS 3.0 approaches multicast a bit differently than earlier versions of the standard, according to CableLabs documentation. Time Warner Cable currently uses DOCSIS 1.1, but Kaul says that a migration path to the later standard exists.

The earlier versions of the standard required that modems "actively participate" in multicast tracking at the networking layer, or layer 3 of the Open Systems Interconnection (OSI) protocol stack. In DOCSIS 3.0, however, the CMTS is in charge, with a flow mechanism that works at the data link layer, with is layer 2. Quality of service (QoS) mechanisms also are added in DOCSIS 3.0.
 
BusinessLink.tv offers NY1 News, CNN, CNN Headline News, CNN International, CNBC, CNBC World, Bloomberg TV, Fox News, Fox Business News, and The Weather Channel, Time Warner says.

—Carl Weinschenk