Whatever happened to Token Ring? Archived e-mail list threads from the late '80s, when telcos adopted LAN technologies en masse, proclaim, "Token Ring is a clear technology winner....Token Ring will trickle down to eventually supplant Ethernet..." Many bet in favor of ARCnet, AppleTalk, FDDI, and other technologies against Ethernet also-and lost time and time again. It makes sense then that Ethernet should be the basis for the next wave of network technology-fiber optic access deployments that combine the benefits of Passive Optical Network (PON) architectures with the staying power of Ethernet. And Gigabit Ethernet PON (GEPON) is emerging as the technology of choice for carriers looking to deploy high-speed, high-density fiber networks today.
Asian Adoption
Ethernet's suitability in the access network, specifically via GEPON, is evidenced by its rapid and accelerating uptake in Asia. Asian carriers are skipping, or have already skipped, the intermediate-and expensive-step of deploying large-scale ATM-based networks. According to research firm Dell'Oro Group, worldwide Ethernet-based PON sales fell just short of $200 million dollars, or roughly 90 percent of total PON sales, in the second quarter of 2005. Japan currently has the largest PON subscriber base in the world. Carrier after carrier in Asia is moving directly to Ethernet, IP, and softswitch technologies to support Internet access, Voice Over IP (VOIP), and video applications. U.S.-based carriers can learn from their Asian counterparts' successes with GEPON, which is readily available and provides cost-effective bandwidth for fiber-to-the-home, fiber-to-the-node, or fiber-to-the-business applications.
Everyone appreciates a good horse race-and that tends to affect much of today's analysis of PON technologies. However, those looking to directly compare GEPON to the nascent Gigabit PON (GPON) standard on a feature-by-feature basis are missing the point. GEPON was never intended to provide native TDM transport, native ATM transport, or overlay wavelengths for video. Rooted in the international standard 802.3ah for Ethernet in the last mile written by the IEEE, GEPON provides the simplicity of Ethernet at Gigabit speeds. The question of deploying GEPON is not one of "this versus that" but rather a question of which technology can most cost effectively support the demands of the applications that carriers need to deploy today and moving forward. Increasingly, carriers are finding that GEPON is that technology.
North American carriers determined years ago that PON architectures make sense. PONs combine the high-bandwidth capacity of fiber with the scalability of point-to-multipoint network topologies. Point-to-point models, like metro Ethernet, have proven to be too costly to scale due to the number of transceivers required in the network and the resulting complexity of management. In addition, PONs save service providers money on the metro/core side of the network. High densities of point-to-multipoint connections on the line side enable more consolidated aggregation on the trunk side by reducing the number of transceivers.
In addition, Ethernet-based PONs provide compound savings. The global adoption of Ethernet for the desktop, for the LAN, and increasingly for the metro area continues to drive Ethernet component costs down. Whereas early ATM-based PON deployments factored out several thousand dollars per subscriber, carriers can now deploy GEPON for well under $500 per subscriber. Lower costs, in turn, reduce the overall capital expenditure a carrier incurs when transitioning to a high-bandwidth PON architecture. Lower costs also accelerate return on investment.
VOIP and IPTV Are Key GEPON Drivers
GEPON technology also represents a forward-looking investment for today's carrier. Several factors are driving voice traffic away from traditional TDM networks and toward VoIP networks. Cable TV giant Comcast announced plans to introduce VoIP service to all of its customers by the end of 2005, prompting competitive responses from the other leading telephone carriers. The regulatory environment in the U.S. continues to be favorable for VoIP, and the traditional technical challenges of reliability and quality of service for VoIP have long been resolved.
Enterprise VoIP deployments are accelerating; Dell'Oro Group forecasts IP PBX shipments at 28 million lines in 2006, exceeding the number of TDM lines shipped. VoIP runs over IP and Ethernet in the metro and core-carriers have already made substantial investments in IP/Ethernet technology to support Internet services. Plus, VoIP originates in native IP and Ethernet at the subscriber terminal, so the need for carriers to deploy PON systems that support lower-layer technologies beyond Ethernet is diminishing. The cable operators' use of VoIP to enter the voice market is prompting traditional telephone operators to use IPTV to enter the video market. As the name implies, IPTV can share a common core, metro, and access network with VoIP. GEPON is thus a smart investment carriers need to make today in anticipation of the continued growth and acceptance of VoIP and IPTV services.
Fiber to the Home
Video, in the context of IPTV, is the premier application for Fiber to the Home (FTTH) and is well served by GEPON technology. Fiber optic local loops built around a PON architecture are currently the best access technology for providing homes with competitive video offerings, high-speed Internet access, and VoIP. This architecture also provides a path to higher per-home bit rates in the future.
A GEPON system with 32 splits can provide 30 Mbps of symmetric bandwidth to each subscriber-more than enough to support bandwidth-hungry video applications as well as voice and data. Even with three high-definition video streams per household, each 6-7 Mbps (or 18-21 Mbps for all three), 30 Mbps leaves plenty of headroom for VoIP and Internet access. The bandwidth budget for VoIP is typically 64K per stream, while high-speed Internet access is tiered at 128 Kbps, 384 Kbps, 512 Kbps, and 1 Mbps downstream (Internet video is migrating from the PC to the television, and thus is already accounted for in the video budget). The total bandwidth needed for all three services comes to less than 25 Mbps. GEPON then is the ideal access technology to support triple-play services today while allowing room for future growth.
Fiber to the Node
In some networks, rapid triple-play turn-up will demand the operator to make use of existing copper, rather than waiting for fiber to be trenched. GEPON has a role to play here as well. A new generation of DSLAM-an Outside Plant (OSP) DSLAM-is already being deployed by many carriers to shorten the length of the copper loop and thereby achieve higher bandwidth from in-situ copper. These OSP DSLAMs will take advantage of the cost savings of PON by implementing a GEPON Optical Network Unit (ONU) function on the DSLAM for the uplink.
This hybrid PON-and-copper Fiber to the Node (FTTN) architecture takes advantage of the cost benefits of PON and the rapid deployment of proven DSLAM technology using in-ground copper plant. Plus, the architecture can support all the same applications-IPTV, VoIP, and Internet access-as FTTH. In addition, FTTN makes an excellent transitional path; if at a later date bandwidth requirements exceed copper access capacity, the cost of further expanding fiber reach all the way to the subscriber's home is greatly reduced.
Fiber to the Business
With IP PBX line shipments expected to soon outstrip legacy TDM PBX shipments, enterprise VoIP represents the next frontier for GEPON-Fiber to the Business (FTTB). Corporate CIOs are discovering the cost savings of VOIP, which comes with little or no sacrifice in voice quality or reliability. Videoconferencing too has a natural synergy with GEPON, taking advantage of the 1 Gbps symmetric line rate. With GEPON, CIOs can finally collapse their individual T1s for PBX, corporate WAN, and Internet access, as well as their legacy ISDN BRIs for corporate videoconferencing, onto an optical Ethernet link provided by a cutting-edge service provider. Furthermore, with Ethernet-based access technologies, CIOs may finally get what they have longed for-scalable bandwidth in the 1.544 Mbps to 45 Mbps range at an affordable price, which is not available on TDM networks.
Ethernet Speed
In 1988, technology pundits were clamoring for 50 Mbps LAN connections to each workstation. Today, 100 Mbps to the desktop is the norm. A few years ago, the 10 Gbps fiber-only Ethernet standard was ratified; now chipmakers are busy at work on 40 Gbps Ethernet. Some would describe these advances as traveling at "Internet speed" but it would be more accurate to describe it as "Ethernet speed." The elegance and extensibility of Ethernet made these high bit rates, and the applications that ride on top, possible. PON access systems provide the ideal path for U.S. carriers to increase bandwidth and services to customers, and when they are combined with Ethernet, as in GEPON, they offer truly scalable, cost-effective service platforms with staying power. U.S. operators that deploy GEPON today will be well prepared for the future.
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