New approaches to FTTP

By David Cleary, Calix -- As the number of FTTP deployments grows, there is greater focus on reducing the risk and cost of the technology. A number of notable advancements are allowing operators to cost-effectively "future-enable" their FTTP networks.

Jul 12th, 2006

As the number of FTTP deployments grows, there is greater focus on reducing the risk and cost of the technology. A number of notable advancements are allowing operators to cost-effectively "future-enable" their FTTP networks.

By David Cleary, Calix

Recent advances in access network technology promise to accelerate the deployment of fiber-to-the-premises (FTTP) infrastructure. These advances fall into two categories: those that minimize technology risks and those that minimize deployment costs. In every case, the advances are a result of the growing base of knowledge gained from real-world FTTP experience.

All consumers have experienced the classical technology procurement dilemma; there is always something better just over the horizon, and maybe I should wait for that. Service providers face a similar dilemma when choosing access network technologies. Unfortunately, the consequences of their purchasing decisions pose a serious risk to their very survival because the network is the lifeblood of the services they deliver.

GPON: Now or later?

Passive optical network (PON) technologies represent an excellent example of this seemingly intractable dilemma. BPON, at 622 Mbits/sec downstream, has been available for some time and exhibits fairly robust interoperability and deployment characteristics. A similar case can be made for GPON at 1.2 Gbits/sec. However, 2.4-Gbit/sec GPON holds the promise of far greater usable bandwidth as well as more comprehensive interoperability. Competitive pressure says, 'Move now.' Service richness says, 'Wait for interoperable and deployable 2.4-Gbit/sec GPON.' Which is the appropriate course of action? Optimally, carriers should find a way to move forward now while retaining the ability to take advantage of new technologies later.

Fortunately, a recent technology advance addresses this dilemma: Auto-detect optics in the optical network terminal (ONT). With this feature, the ONT automatically detects the PON speed (622 Mbits/sec, 1.2 Gbits/sec, or 2.4 Gbits/sec) and the PON protocol (BPON or GPON) and matches the required operating parameters. This advancement allows service providers to deploy ONTs now in 622-Mbit/sec BPON or 1.2-Gbit/sec GPON mode and automatically up-shift to 2.4-Gbit/sec GPON when the operator is ready to upgrade the optical line terminal (OLT). This neatly sidesteps the dilemma of when to implement 2.4-Gbit/sec GPON.

Since ONTs represent the bulk of the cost and complexity associated with FTTP, finding ways to deploy them today and continue to utilize them later allows service providers to move forward with an "insurance policy" that protects their initial ONT investment. Marketing folks often--and incorrectly--refer to this as "future-proofing," as if the technology prevented the future from coming. In fact, what this represents is "future-enablement," a method of moving forward while retaining the ability to take advantage of new technologies as they arise.

The auto-detect optics described here are not the same as upgrading an ONT through software download. Software downloading a PON protocol to an ONT requires a system re-boot. This forces operators into a "Hail Mary pass" situation where all they can do is hope the upgrade occurred with all the ONTs. With auto-detect optics, the ONT can be switched back and forth between PON speeds and protocols without a software upgrade.

Minimizing risk with FTTN

Another technology currently in use to minimize the risk of FTTP is actually a competing architecture. For the most part, service providers today are opting for one of two broad architectural approaches for transforming their access networks to handle richer, more fully integrated information, communication, and entertainment services. One approach is FTTP, which drives fiber all the way to the customer premises. A second approach is to pull fiber only partway to the premises and thus reduce the size of the customer serving area (CSA) from 10,000-12,000 feet to 3,000-5,000 feet. The fiber-to-the-node (FTTN) approach employs VDSL2 to get downstream bandwidth in the 25- to 40-Mbit/sec range over the final few thousand feet of copper.

FTTN has long been viewed as antithetical to FTTP. However, even service providers deploying FTTN access infrastructure recognize that, eventually, fiber will be pulled all the way to the customer premises. Further, FTTN architectures mandate that service providers pull a great deal of additional fiber deeper into the access network. FTTN deployments potentially require 4-8 times as many nodes as architectures based on traditional remote terminals (RTs). Viewed this way, FTTN becomes yet another interim step on the road to an all-fiber network. The challenge for many service providers is that the dominant network element used to build out FTTN access networks--the IP DSLAM--does not afford them the flexibility necessary to move to FTTP when it becomes attractive to do so.

Fortunately, newer network elements purpose-built for FTTN applications fully consider the environment in which they are placed. These network elements, sometimes called IP service edge nodes (SENs), are typically placed at serving area interface (SAI) cross-connect locations. These non-powered pedestals groom copper feeds back to the central office (CO) or RT. In many FTTP builds, the SAI also is the location where the passive splitter is installed, since rights of way (ROWs) and wiring facilities already are available there. Placing an IP SEN at these locations as part of an FTTN build places the service provider in an advantageous position to deploy FTTP at a later date. The FTTP deployed from an FTTN location may be either passive or active for residential and business applications, respectively. Figure 1 illustrates how this migration from FTTN to FTTP could take place.

Both of these technical developments--auto-detect optics and flexible FTTN SENs--recognize that the greatest challenge facing service providers today is the rapid rollout of enhanced information, communication, and entertainment services to better compete with cable and satellite providers. Any network infrastructure investment should be targeted first and foremost at enabling those services. There are myriad approaches that might be used to realize this goal; some are available now, others in the future. What is most important in terms of technology selection are speed and flexibility. Speed is the ability to roll out these services now, and flexibility is the ability to take advantage of technical developments downstream without making wholesale network changes. Auto-detect optics and flexible FTTN platforms satisfy these objectives.

Minimizing deployment costs

Outside plant costs and OLT/ONT costs once received the most scrutiny when budgeting an FTTP project. However, as these costs have declined over time, other previously overlooked costs now are being re-examined. Virtually all aspects of the FTTP lifecycle are undergoing cost reductions, two of which are particularly noteworthy: Butt-set provisioning and IP-over-Coax.

Butt-set provisioning refers to a means for correlating a subscriber record with a specific ONT. In any PON application, the OLT identifies each ONT by its unique serial number. Pre-provisioning ONT serial numbers is cumbersome because it requires a craftsperson to install an ONT with a specific serial number at a specific address. Butt-set provisioning allows the craftsperson to install any ONT at a residence and use any common keypad device to enter subscriber-specific information.

Another FTTP deployment cost under scrutiny is inside wiring for IPTV. Traditionally, Category 5 cables were installed from a central switch to every TV in the residence. Although this is an unskilled tasked, it takes considerable time given customers' dislike for unsightly cables. A high-tech alternative, IP-over-coaxial-cable, is replacing this process. Two comparable protocols for this technique, HPNA and MoCA, both rely on existing in-home coaxial cables to transport IP/Ethernet to set-top boxes.

As the number of FTTP deployments grows, there is a greater focus on reducing the risk and cost of the technology. A number of notable advancements are changing the way operators deploy this access technology. Auto-detect optics in the ONT and flexible FTTN service edge nodes are two advancements that reduce the technology risk of FTTP, while improved design and enhanced features such as IP-over-coax are pushing down deployment costs. The trend toward greater innovation in the FTTP market will accelerate from this point on--and that is certainly good news for the service provider.

David Cleary is vice president, advanced technology at Calix (Petaluma, CA). He may be reached via the company's Web site at www.calix.com.

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