Compatibility is the key to FTTH success

Aug. 1, 2007

by Reuven Segev

Rising demand for domestic network services and bandwidth is making FTTH an increasingly attractive option for service providers. GPON offers carriers the most promising FTTH implementation strategy. Experience has shown, however, that interoperability among vendors’ products will be essential to growing the market and that vendors entering this space must demonstrate such interoperability quickly to achieve success.
Figure 1. The amount of bandwidth residential users are expected to consume continues to grow.
The case for GPON

Consumer data traffic is continually on the rise as consumers continue to embrace the World Wide Web (see Fig. 1). In addition, growing interest in streaming media, voice over Internet Protocol (VoIP), IP-based television, and the like are raising the bandwidth requirements that consumers expect service providers to meet.

Meanwhile, wire-based technologies such as DSL are reaching their limits. The range that any DSL approach can achieve decreases as link bandwidth increases (see Fig. 2). This decreasing range reduces the number of residences that a DSL implementation can serve, placing service providers in the dilemma that by increasing their service bandwidth they reduce their customer base. The higher-performing and once-competing ATM approach that might have taken up the bandwidth challenge has essentially vanished as telecommunications providers embraced IP for virtually all traffic.

The residential market thus must embrace a new delivery technology. PONs, originally rejected by the market as too expensive due to the need for installation of a fiber-optic cable infrastructure, are now being reconsidered as the means to solve the bandwidth challenge. As fiber deployment costs continue their downward spiral and the need to install a new delivery infrastructure seems inevitable, the original objections to PON become weaker and weaker.
Figure 2. As bandwidth rates rise, DSL reach drops significantly. Carrier requirements will soon outstrip DSL’s capabilities-if they haven’t already.

Able to deliver 2.488 Gbits/sec downstream and 1.244 Gbits/sec upstream, GPON offers the most viable approach to solving the bandwidth challenge. A single optical fiber from the central office (CO) can serve as many as 64 end users over runs as long as 20 km, keeping infrastructure costs down. Fiber also provides low noise, achieving multigigabit data transmission with very low error rates.

None of this depends on any technological breakthrough; it is available now. A robust set of standards was ratified in 2006, and deployment has begun. In the United States, AT&T, Qwest, Verizon, and hundreds of second- and third-tier independent operating companies have all begun the deployment of GPON and FTTH infrastructure and services. Operators in China, France, India, Italy, and South America have begun trials with plans to install infrastructure and implement services when trials are concluded.

When considering the implementation of FTTH using GPON, however, system vendors should look to the lessons of DSL implementation for guidelines on how to proceed. During the early days of DSL implementation standards were unclear, allowing implementation variations that met the standard but did not necessarily work together. As a result, service providers had to control both ends of the link-CO optical line termination (OLT) equipment and the consumer premises optical network termination (ONT) equipment-in order to ensure that the DSL link would perform satisfactorily. As result, initial contracts required system vendors to supply both CO equipment and customer premises equipment (CPE).

While this model worked initially, consumer market dynamics did not support its continuation. Both service providers and their subscribers wanted choices, service providers for the ability to differentiate themselves with the services they provided and subscribers for cost and support issues. The resulting demand for more options in DSL created a free-for-all that quickly split the DSL market into two segments: DSLAMs (CO side) and CPE. A small set of telecommunications equipment manufacturers (TEMs) sold DSLAMs and related CO equipment to the service providers and a larger number of original equipment manufacturers (OEMs) began selling DSL CPE in retail outlets.

This represented a critical time for DSL adoption. Customers of both types wanted “out-of-the-box” success with equipment that they purchased, and the implementation variations stemming from the specification weaknesses threatened that success. To achieve widespread acceptance of DSL, therefore, both OLT and ONT equipment vendors had to ensure interoperability of their products with those of their competitors. This required a significant industry effort, including massive multivendor “plug-fests” to test interoperability and resolve differences. Now, guaranteed interoperability is essential to participation in the DSL market.

GPON is in a situation similar to the early days of DSL. The specification’s richness makes implementation variations inevitable, raising once again the specter of poor interoperability. Initial installations will have service providers handling both ONT and OLT equipment. As with DSL, however, market forces will favor splitting the two equipment markets. System vendors will exit the ONT market and leave it to ODMs specializing in high-volume CPE.

Unlike DSL, however, the pace of FTTH acceptance will be fairly rapid. Consumers have already embraced the Internet. The acceptance of DSL technology opened the market for home networking, and from the consumer’s viewpoint FTTH is simply a performance upgrade with new features. Thus, there is no longer an initial market creation hurdle to overcome.

In addition, each new generation of networking technology has seen more rapid adoption than its predecessor. It took ADSL five years to move from field trials to mass deployment. VDSL took only three years to reach the same point, and BPON adoption took two years. The adoption of GPON is poised to begin mass deployment only one year after trials.

This leaves potential vendors in a precarious position. The technology’s complexity makes inevitable some variations in implementation as vendors bring their first products to market. Yet operators and subscribers will demand the “out-of-the-box” success they now enjoy with DSL or they will reject the technology. Thus, a speedy path to interoperability among GPON vendors will be necessary both for individual vendors and for the market as a whole to succeed.

Yet the traditional path to interoperability, custom designs followed by plug-fests, is anything but fast. In addition, the standards for GPON are more complex than DSL, imposing a high R&D startup cost and a longer learning curve. Acquiring the necessary optical communications background and expertise will require more than a year for companies starting from scratch. The accelerating rate of technology adoption means that the window of opportunity for entering this market will close quickly. Vendors will need to get to market rapidly or not at all. Those just entering will thus need a means for bypassing the development effort, time, and cost to gain a foothold. Further, this bypass must ensure interoperability with the market leaders.

The fastest and most reliable method for bypassing startup efforts is to use outside expertise rather than developing it in-house from scratch. For OLT equipment, companies need an optical design, an efficient and highly integrated MAC (to reduce cost), and GPON software to provide such functions as network management and dynamic bandwidth allocation. For the ONT CPE, companies need a complete hardware design with GPON, optics, data communications bridge, VoIP and IPTV software, and optionally an RF overlay for wireless networking within the home from an outdoor line termination unit. Using ONT and OLT equipment developed by the same vendor will ensure interoperability in the first phase. Using offerings with proven interoperability will be essential to stay in the market during the second phase.

Leveraging an existing design offers many advantages. It eliminates the need to gain optical expertise because the optical network interface becomes simply a “black box” to the developer. It can reduce time-to-production to as little as three to six months because the design is tested, proven, and documented with full fabrication details. Rapid attainment of industry-wide interoperability is also assured when leveraging an existing, proven design. When a large number of vendors start with the same basic design, only a few implementations need to be tested together and incompatibilities resolved.
Figure 3. Vendors can pair GPON SoCs and other IP and technology with in-house expertise to create differentiated offerings.

Having a multitude of vendors using the same design, however, often leads to concerns that the products will rapidly become low-profit commodities. That is not the case with GPON. Only the optical network interface and GPON layers need standardization. The remainder of the design, including user interfaces, feature sets, and overall cost/performance tradeoffs, can still be unique for each vendor. Thus, for OLT vendors, there is a natural separation between the acquired design elements and the unique elements (see Fig. 3) that allow the vendor ample opportunity to differentiate its products and add unique value while obtaining guaranteed interoperability. For CPE vendors, adopting a standard design is common practice to minimize the R&D expenses they need to recover. Instead, CPE vendors compete by leveraging their manufacturing and distribution expertise. Both markets, therefore, can benefit from adopting existing designs.

For existing designs to be de facto implementation standard candidates, however, they must have several important attributes. One of the most critical is that they be part of a full system approach rather than simple point products. The simple, single-component vendor paradigm is not sufficient to guarantee interoperability and quick time-to-market. Instead, the ideal approach will include both ONT and OLT designs to guarantee interoperability and be ready to drop in and move to production.

This need for a comprehensive approach implies that the standard designs should come from a source with expertise in the applications environment as well as GPON technology. The technology and intellectual property must reflect the needs of data, carrier-grade voice, and streaming media such as IPTV to ensure that OLT and ONT equipment based on the design will have attributes needed to maximize performance in these essential applications. They should also be flexible and feature-rich to enable differentiation and innovation by the vendors that adopt them.

A specific design attribute important to OLT vendors is the availability of a seamless interface to packet switch hardware. This attribute can be achieved by using a standard interface such as XAUI or SGMII. Having a standard interface simplifies the integration of the TEM-specific portion and the GPON interface.

For ONT vendors, especially, the standard design must also be production ready. This includes complete mechanical and electronic hardware designs, bills of material (BOMs), assembly and test documentation, and application software. In addition, any ASICs and other critical system chips must be readily obtainable.

Finally, the standard design must be both proven and immediately available for OEMs and TEMs that are late to the market to become competitive quickly. Fortunately, GPON “ecosystems” that meet these requirements are available. Such ecosystems provide a complete set of designs, SoCs, software, and manufacturing support for both ONT and OLT GPON blade interfaces. TEMs and OEMs can call upon sustaining engineering support services throughout the life cycle of each product design as well.

The technological capabilities of these ecosystems are quite robust. For example, the GPON section of OLT blades for TEMs to integrate into their CO product platforms can include either a dual-PON or quad-PON SoC along with a complete GPON management software suite. A detailed, production-ready reference design, including BOM, electrical design, and production and test files, speeds the adaptation of existing blade designs to incorporate the GPON front-end.

The availability of such standard designs will prove key to the market success of GPON and FTTH. More OLT and ONT equipment vendors will be able to enter the market with compatible designs and accommodate the market’s rapid development. This proliferation of compatible designs will accelerate industry-wide interoperability. This interoperability, in turn, will ensure that expectations of vendor choice and out-of-the-box installation success are met, which is essential for the market to thrive.

Reuven Segev is vice president of marketing and business development, North American and South American regions, at iamba Networks (

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