Digital return: Technology for tackling the DOCSIS 3.0 return path conundrum

John Dahlquist, Aurora NetworksAs cable operators continue deploying DOCSIS 3.0 services to connect homes and businesses, they face a big conundrum: The return path.

With cable operators using upstream and downstream channel bonding to deliver DOCSIS 3.0 services, ensuring there is sufficient upstream performance to support robust DOCSIS 3.0-supported offerings remains a challenge. Full implementation of DOCSIS 3.0 in the upstream includes the bonding of four 6.4 MHz channels along with increasing the modulation level from the popularly deployed 16 QAM to 64 QAM; both dramatically increase the performance required from the upstream lasers which had previously been largely unstressed.

To overcome this hurdle, many cable operators are deploying digital return technology. Digital return enables a cable operator to provide 100 Mbps in upstream data speeds in DOCSIS 3.0 deployments, in some cases matching the average speeds available in the downstream.  Digital return technology also allows cable operators to keep DOCSIS 3.0 deployment costs in check and provides an evolutionary path for future upgrades.

Developments in digital return technology now enable cable operators to cost-effectively replace reverse analog links supporting high-speed Internet services with digital links.  By digitizing a single RF return and combining it with several Ethernet channels, or taking two digitized return segments and time division multiplexing them into a single return, cable operators can cost-effectively put in place a digital transport mechanism that addresses the shortcomings of their current analog return systems.

CMTS cost is another consideration: Higher aggregation requirements are driven by a need to limit the deployment cost of DOCSIS 3.0 systems to just the replacement cost of a DOCSIS 2.0 system, deferring the service enhancement cost until it is needed to offset competitive threats or driven by higher capacity demand (revenue increase).

 CMTS deployments are among the more considerable costs for launching and expanding broadband services.

Digital return solves the return path performance issues associated with DOCSIS 3.0 roll-outs. Indeed, cable operators launching DOCSIS 3.0 services with digital return technology also can future-proof their CMTS technology investments. CMTS deployments are among the more considerable costs for launching and expanding broadband services. Cable operators can alleviate some of these costs by combining upstream links to preserve CMTS port usage until really required.

In addition, digital return provides a high level of scalability, from return concatenation to full segmentation, providing cable operators with a compelling, fiber-efficient solution. The technology also will support higher modulation schemes, for example, 256 QAM.  This lays the foundation for future generations of DOCSIS services.

Upstream channel bonding is a relatively new tool for cable operators rolling out faster high-speed Internet offerings.  However, some systems already are achieving significant headway with their use of upstream channel bonding.

Recently, Canadian cable operator Videotron rolled out DOCSIS 3.0 services in its Quebec City market that deliver 120 Mbps in the downstream and 20 Mbps in the upstream.  To obtain the upstream speeds, Videotron is bonding four channels in conjunction with 64 QAM.

The aggressive rollout of DOCSIS 3.0 services continues, creating more demand for an upstream-enhancing solution such as digital return.  Comcast, for example, has more than 80 percent of its plant upgraded for DOCSIS 3.0 capabilities.   

Cable operators offering DOCSIS 3.0 services built on digital return technology ensure current and future high-speed data deployments and upgrades are supported without costly and time-consuming changes to their current network infrastructure.  Digital return provides a future-proof path for cable operators as they evolve their DOCSIS 3.0 services and does this at a very small additional cost when compared to today's most advanced analog links.

Most importantly, digital return resolves the return path conundrum for cable operators, guaranteeing residential and commercial services customers have access to the most compelling, robust high-speed Internet services available in the market, both today and tomorrow.

John Dahlquist is Vice President of Marketing for Aurora Networks.

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