As we all know, broadband providers of every stripe are deeply engaged in the process of evolving their networks to support gigabit access capabilities. This evolution is driven by a need to address skyrocketing bandwidth demands; both residential and business subscribers increasingly expect robust broadband services including IP-based streaming video and cloud-based applications.
A variety of industry dynamics are motivating MSOs to re-architect their access networks with higher performance technologies. Such dynamics include the rapid proliferation of connected devices of all kinds (TVs, smartphones, tablets, and more), competition from new entrants such as Google and other players building out gigabit networks over fiber, and the rapid growth in over-the-top (OTT) applications.
Cable operators also face the challenge of the shift to higher quality streaming video standards, such as 4K resolution, and the rapid adoption of cloud services — both of which will ultimately increase bandwidth requirements further.
Whatever the reason, the reality is that cable networks need to evolve, quickly, to remain competitive. A broad consensus has emerged in the industry that the future of ultra-broadband access is fiber. Among cable MSOs, however, the question of what path to take to that future, and when that future will arrive, is a topic of much discussion.
Cable MSOs are in a somewhat unique position — compared to their telco brethren — because their evolution begins at a very different starting point. As important, the path to the fiber future will differ based on the customer segment vs. urban, greenfield vs. brownfield) as well as other factors.
When building out or expanding the access network, cable MSOs can choose among several different options, ranging from upgrading their hybrid fiber/coax (HFC) networks to deploying or extending fiber-to-the-home (FTTH) sooner rather than later.
Let's explore some of these paths.
PON for cable
In many markets cable MSOs are leaders in the delivery of broadband residential entertainment and communication services. Many are also quickly building their footprints in the business services market where there is a rich and growing opportunity. To expand their share of the business services market, MSOs around the world are increasingly looking to passive optical network (PON) technologies.
Many MSOs have taken a gradual, staged approach, starting with building out their fiber networks to first serve business customers, then extending fiber into residential areas as required. In some cases, such as greenfield residential areas or highly competitive markets, select cable operators are building FTTH networks.
To date, a popular approach to PON deployment for MSOs has been a combination of Ethernet PON (EPON) and CableLabs' DOCSIS Provisioning of EPON (DPoE). DPoE makes the EPON network fully transparent to existing OSS/BSS systems, simplifying integration and management of the network and thereby removing a very large barrier to adopting this cost-effective approach. DPoE does this by virtualizing the management aspects of the cable modem termination system (CMTS), and even the cable modem itself, while providing a DOCSIS-compatible interface to the operator.
DPoE allows operators to continue to use the existing billing system and diagnostic and service assurance tools that they have used for their DOCSIS network. By decoupling the access technology from the management interface, DPoE immediately enables operators to support a future-proof fiber access network without affecting the existing back-office environment.
EPON has proven an effective way of increasing broadband speeds substantially, with basic EPON providing 1-Gbps symmetrical bandwidth and supporting multiple 100+ Mbps connections on a single fiber. Because the bandwidth is symmetrical, EPON is well suited to supporting commercial services between branch offices and data centers. Adoption of EPON also means MSOs already have the ability to deliver even higher-speed service through support for 10G EPON, which can provide 10-Gbps symmetrical bandwidth to cover the needs of multiple 1+ Gbps connections, and also offer support for DPoE.
Cable operators also have the option to use the most widely deployed form of PON technology, Gigabit PON (GPON), which delivers a bandwidth of 2.5 Gbps downstream and 1.25 Gbps upstream. A number of MSOs around the world have selected GPON — supported by an all-IP network — as their fiber access technology of choice, typically for greenfield buildouts and/or business services.
Ultimately, adoption of a PON architecture sets the stage for cable operators to ride the wave of PON technology evolution. Time and wavelength-division multiplexing PON (TWDM-PON) is anticipated to be the technology for the new NG-PON2 standard, the latest, most advanced form of fiber-based access technology. It stacks multiple wavelengths on the same fiber, with each wavelength providing a variety of upstream and downstream bandwidths: 10G/2.5G, and 10G/10G. First-generation products stack four different wavelengths, with up to eight in the future.
Looking even further, there is work underway in the IEEE toward establishing an NG-EPON standard, which will incorporate many of the concepts and requirements from the NG-PON2 standard, with a goal of achieving speeds from 25 Gbps to 100 Gbps.
Building on the DOCSIS legacy
The other prominent broadband technology option available to cable operators is DOCSIS 3.1, an emerging CableLabs specification designed to overcome the upstream and downstream bandwidth limitations of current DOCSIS technology. DOCSIS 3.1 promises substantial improvements in terms of throughput using existing HFC access infrastructure, supporting up to 50% more data over the same spectrum. With this upgrade, cable providers should be able to deliver up to 10 Gbps downstream and up to 1 Gbps upstream — if all the necessary grooming and upgrades have been made to the cable plant, networking equipment, and CPE.
CableLabs has indicated that this approach is expected to yield efficiency benefits that would decrease the cost per bit for data transport through spectrum efficiency improvements as well as latency reductions, which would improve the performance of real-time applications like online video gaming. Operators can also expect to see some energy efficiency improvements in cable modems.
One of the key benefits of this approach is that any new DOCSIS 3.1 equipment will also be backward compatible with existing DOCSIS-based technology already deployed in operators' networks. Additionally, cable MSOs will be able to re-use substantial elements of their infrastructure.
However, field experience with DOCSIS 3.1 deployment at scale is still quite limited, so it is difficult to predict the full upgrade cost at this time. What is clear is that there will need to be significant conditioning of operators' cable plants, which would certainly entail substantial cost.
The ideal path?
As with most such exercises, upgrading to DOCSIS 3.1 or going straight to FTTH is a business decision, and the assessment will differ from operator to operator based on their competitive environment, the state of their HFC network, market dynamics, and more. In short, there is no ideal path and many upgrades will be done in select locations. Therefore, operators will have to support hybrid networks that are not purely based on HFC and DOCSIS technology.
However, there is an ideal destination. In the end, cable MSOs will need fiber access networks to compete with other broadband providers that are delivering services over fiber. In the not-too-distant future, it is possible that NG-PON2 (in the form of TWDM-PON) will be commonly used for broadband access infrastructure, and there will be broadband providers that will move quickly to offer the high-speed, high-capacity links this technology can offer. In addition, TWDM-PON systems will provide operators the flexibility to logically segment their access network to support different types of services &mdash such as residential, business, and mobile/Wi-Fi backhaul — with different associated service level agreements..
The decision point cable MSOs face is whether to make the investment to transition to a pure fiber approach today, begin the transition (using DPoE) to continue to leverage their DOCSIS back-office systems while building out their fiber footprint, or focus their near-term efforts on sweating their DOCSIS and HFC assets for as long as possible, recognizing that eventually they may need to go all-fiber.
Whichever path they choose, there is no time for delay. The broadband future is coming — and it may be coming faster than we think.
David Eckard is CTO of Fixed Access Business at Alcatel-Lucent. The Fixed Networks Division represents both the copper and optical access products for Alcatel-Lucent. Dave is a Distinguished Member of the Technical Staff, holds several patents in optical access, and has represented Alcatel-Lucent at ITU and FSAN standardization forums for next-generation optical access networks.