FTTH Explained: Delivering EfficientCustomer Bandwidth and Enhanced Services

Telecommunication carriers worldwide have come to the realization that their aging copper access infrastructure is being taxed as residential and business customers utilize ever-increasing, symmetrical bandwidth-intensive applications. The telecommunications landscape has matured to a point that carriers seek to offer network convergence and enable the revolution of consumer media device interaction. These demands are being met by the deeper penetration of optical fiber in access networks and increasing deployment of fiber-to-the-home (FTTH). As a result, FTTH is the fastest-growing global broadband technology, with significant deployments in Asia, Europe, and North America. 

  

Introduction

The twenty-first century heralded countless changes across our landscape; arguably none will be more important than the transformation of our telecommunications providers' means to deliver services to residential and business consumers. This phenomenon is being underpinned by two technologies: Internet protocol (IP) and optical fiber. Today, the technology is available to provide voice, video, and data services over a common protocolIP. 

Carriers are quickly moving to maximize the number of services they offer to a single customer via a bundled offering. Technologies such as voice over IP (VoIP), IP television (IPTV), and broadband are becoming commonplace across the world. As bundled services and technologies are deployed, carriers are realizing that their original networks, designed to efficiently deliver a single service, are stressed and in many cases incapable of offering the desired services. Figure 1 depicts forecasted subscriber service and bandwidth demand (note new compression schemes include MPEG-4 and Microsoft Windows 9/VC1). Today's networks are being designed to provide more than 20 megabits per second (Mbps) while three to five years from now, carriers will need capability of more than 40 Mbps as multiple services are used in the home, high-definition TV (HDTV) becomes more prevalent, and users demand faster Internet connections. This is resulting in the largest investment in the access network since the turn of the century and the wiring of the western world for voice services. 

Leading this investment wave is the deployment of single-mode optical fiber deeper into these access networks to curb the high bandwidth requirements of their customers. Increasingly, carriers are finding that deploying the fiber all the way to the customer enables network future-proofing, maximizes the symmetrical bandwidth throughput of a carrier's access network, provides for network reliability, reaps significantly reduced operating expenses and affords enhanced revenue opportunities. The industry refers to this technology as FTTH. 

FTTH Outside Plant Components

All FTTH networks inherently are designed to deliver an optical fiber to the subscriber. However, their design is highly dependent on the unique nature of the access environment, so product and design flexibility is critical. At their core, FTTH networks contain an optical line terminal (OLT), optical cable, and optical network terminal (ONT). Various other specialized components are added to address the unique nature of the access network. 

The optical fiber carries the signal to the user and is divided into three sections: feeder cable (terminated at the CO/HE), distribution cable (fanning out across the access network and connect to the feeder cable “feeds”), and drop cable (used to physically connect the users to the FTTH network). As a medium, optical fiber's bandwidth is only limited by the transmitters of the OLT and hence future-proofs the access network because of its tremendous bandwidth capacity. 

As discussed, PTP networks are characterized by their simplicity. A PTP network minimizes the number of components in the field and has all the items described above as well as enclosures used to connect the multiple cables deployed in the field. PON networks more efficiently utilize the optical fiber in the field and the transmitters of the OLT. Therefore, their design is more complex than PTP. 

Beyond the OLT, optical cable and ONT, the PON includes many specialized components that serve to address the cost, deployment, and reliability concerns of earlier FTTH deployments. The most important of these is the optical splitter. Depending on the split architecture chosen, splitters can take the form of 1x32, 1x16, 1x8, 1x4, or 1x2 and can be almost anywhere in the access network. As discussed, many carriers choose the centralized split architecture. 

A recent standardized innovation in the drop cable and NAP is the use of environmentally hardened connectors. Legacy networks connected all the optical fibers of all access components with an optical splice, either mechanical or fusion. While typically introducing little optical loss into the network, the splice introduced high cost into the network deployed because of the time involved to achieve one splice and the technician skill level and equipment deployment requirement. Connectors eliminate these costs, greatly improving deployment velocity while introducing little loss into a network because of the short loop lengths inherent in access networks. FTTH network connectors are standardized technology governed by Telcordia GR-3120. 

FTTx Explained

The industry today has earmarked the general penetration of fiber into the access network as FTTx. This has created some confusion, though, as FTTx covers several architectures and protocols. In fact, some of today's digital subscriber line (DSL) and hybrid fiber coax (HFC) networks qualify as FTTx networks because of their use of fiber in the access, as does a PON. Hence, it is best when referring to a deep fiber penetration network to refer to its actual architecture. The most common architectures are fiber-to-the-home (FTTH), fiber-to-the-building

(FTTB), fiber-to-the-curb (FTTC), and fiber-to-the-node (FTTN). Each of these has a different physical architecture. 

As we have discussed extensively, FTTH pushes fiber all the way to individual residential dwellings. FTTH is completely free of copper in the outside plant and typically provides for 30 to 100 Mbps service, but because of the inherent characteristics of optical fiber, it can provide literally infinite bandwidth. FTTB typically uses the PTP architecture in the outside plant, providing a dedicated fiber to each building or block of buildings. The fiber is terminated at a remote terminal (RT), which is an active device requiring powering and security typically in the basement, communications room or utility closet. If the building is outfitted with CAT5 cable to each dwelling unit, an Ethernet local-area network (ELAN) is installed to provide shared bandwidth of 10 or 100 Mbps. If twisted pair is only available, the RT is a digital subscriber line access multiplexer (DSLAM) and is installed to provide requirement bandwidth services offering up to 50 Mbps. 

FTTC typically pushes fiber to about 500 to 1,000 feet from the subscriber, terminating at an RT and serving eight to twelve subscribers. FTTN is similar in architecture to FTTC except that the RT is positioned much further from the subscribersup to 5,000 feetand will serve three to 500 subscribers. Both utilize existing twisted pair outside plant to connect to the customer. Bandwidth is dictated by DSL technology and copper loop length. Very-high-data-rate DSL (VDSL) and VDSL2 works best at longer loop lengths and is predominantly used for FTTN, while symmetric DSL2 (ADSL2), 2+ and 2++ are being used in today's FTTC systems. Signals over copper significantly degrade over long distances, directly affecting the bandwidth capability. In the most extreme conditions (four to five km), some customers may not even be able to be served by DSL. If copper conditions warrant in some cases, the carrier will use both twisted pairs to boost the bandwidth throughput. Both architectures have afforded about 20 Mbps service in the laboratory. Due to shorter copper loop lengths in a FTTC network, the operator has improved scalability from a bandwidth perspective. Large-scale deployments of FTTC and FTTN are planned in the future. 

Fiber penetration directly correlates to the bandwidth throughput of each defined architecture and, therefore, the service capability for the operator. As discussed earlier, the bandwidth requirements of each carrier differ, but all are growing. The carrier must take this into account as it deliberates over the desired architecture to deploy. Fiber penetration is also an indicator on the capital expenditures (CAPEX) and operating expenditures (OPEX) expected. Deep fiber will result in a higher CAPEX for existing neighborhoods, but is actually near cost parity with all architectures for new builds. Deep fiber will deliver the maximum amount of OPEX savings comparably. FTTH enables the delivery of savings because of reductions in cost for network, central office, and outside plant operations as well as customer service. Network reliability dramatically increases as well, with FTTH ensuring a steady stream of revenue and enhanced customer satisfaction. 

Summary

Carriers from Boston to Berlin, and Seoul to Sydney are faced with an access network problem on how to upgrade an access network that is currently considerably taxed by the need to provide more bandwidth to residential and business consumers. Universally, carriers are choosing to place fiber deeper in the access network to overcome the limitations of copper but are faced with myriad architecture choices. 

Today, many are investigating the deployment of FTTH, whether it is PON or PTP, centralized split versus distributed, while still many more are in the midst of rehabilitating significant portions of their access network with FTTH. FTTH is being chosen because it maximizes bandwidth to the residence; future-proofs one's network; and provides for enhanced network reliability, increased customer satisfaction, expanded service capability, and improved network OPEX.

Source: http://cablequest.org/articles/ftth/item/1410-ftth-explained-delivering-efficientcustomer-bandwidth-and-enhanced-services.htmlSource: http://cablequest.org/articles/ftth/item/1410-ftth-explained-delivering-efficientcustomer-bandwidth-and-enhanced-services.html