Digital Return: Addressing The Upstream Challenge

Today’s dependency on the Internet coupled with the influx of innovative, wireless-enabled devices that connect to the home broadband network has created an overwhelming need for faster speeds. This demand, combined with the increase in competition among communications service providers (CSPs), has created a battle over who can provide the fastest and most compelling services to customers.

Broadband Internet access has become a critical competitive differentiator as cable operators are tasked with delivering faster speeds and seamless quality of experience to customers. The cable industry turned to DOCSIS 3.0 technology as a way to address speed through upstream and downstream channel bonding.  However, as much as DOCSIS 3.0 technology has enabled operators to successfully compete in the race for speed, there still remain challenges in the technology’s upstream channel-bonding process.

While downstream channel bonding is easily achieved, ensuring there is sufficient upstream performance to handle the robust DOCSIS 3.0-supported offerings is quite the hurdle for operators to overcome. This hurdle is driven both by the technology’s higher modulation scheme of 64 QAM (previously 16 QAM) and the requirement to channel-bond as many as four 6.4-megahertz channels in order to support higher-speed data rates that range to 100 Mbps. The result is an increase in performance requirements from the upstream link, which previously had been adequate.

The Options

There are three common return-path technologies that operators have implemented for upstream transmission: Fabry-Perot lasers, analog distributed feedback (DFB) lasers and digital return technology. 

Of the three, Fabry-Perot is the most limited, as it cannot support bonded channels over any reasonable distance.  This limitation is further proved if the operator needs to combine upstream links to maintain a cost-effective deployment of a DOCSIS 3.0 CMTS platform. 

DFBs have greater capability than do Fabry-Perot; however, there still are reach limitations, as it cannot support distances greater than 20 kilometers at 1310 nanometers.  In addition, DFBs don’t have the capability to support future generations of DOCSIS services, which would place even greater demands on the upstream optical link.

These limitations have driven cable operators to examine digital-return technology. 

The Advantage

Unlike the previous two options, the increased performance capabilities of digital-return technology enables cable operators to provide greater-than-100-Mbps data speeds in DOCSIS 3.0 deployments and, in some cases, to provide the ability to match the average downstream speeds. These data rates are particularly important when competing with advanced services offered by telcos, including Verizon’s FiOS and AT&T’s U-verse offerings. 

Digital-return technology provides cable operators with a cost-effective way to overcome the performance challenges of DOCSIS 3.0 upstream channel-bonding.  Digital return also provides a high level of scalability, from return concatenation to full segmentation, giving cable operators a compelling, fiber-efficient solution.  The technology supports higher modulation schemes, as much as 256 QAM, thus laying the foundation for future generations of services requiring even higher capacity.

Additionally, digital-return technology resolves such return-path performance issues associated with DOCSIS 3.0 rollouts as the ability to future-proof CMTS technology investments. CMTS equipment is one of the highest costs operators face when launching and expanding broadband services.  As such, many operators have come to rely on higher link aggregation, deferring DOCSIS 3.0 system deployment costs until it is needed to offset competitive threats or provide higher capacity. Cable operators launching DOCSIS 3.0 services with digital-return technology can alleviate some of these costs by combining upstream links, allowing them to preserve the CMTS port usage until it really is required.

Optimum Solutions

As the industry dives deeper into providing subscribers with next-generation services that rely heavily on upstream data capabilities to further the technology evolution, it is important that cable operators deploy solutions that provide the flexibility required to adapt to these new services.  By deploying digital-return technology, cable operators can be assured that their customers will have access to the most robust, high-speed services available in the market, today and tomorrow.

John Dahlquist is vice president/Marketing, Aurora Networks.