Dr. Robin Grindley，Teknovus, Inc.
The Access Network consists of two main market segments: business and residential users. Business users are willing to pay for premium services such as higher bandwidth, quality of service and reliability. The Residential market segment is driven primarily by cost, although recent trends indicate that residential users are unwilling to tolerate low bandwidth, even if the cost is very low. czw光波通信
czw光波通信
The Access Network has historically been dominated by DSL and Cable technologies in the residential market and point-to-point lines (fiber, copper or microwave) in the business services market. While the term 搇ast mile is used to refer to the Access Network, this is a bit of a historical misnomer. In order to reduce the number of (expensive) central office sites, carriers have been pushing the access networks reach up to 20 km and beyond. As carriers increase the length of the Access Network, reliability of the cable plant itself becomes an issue. Carriers do not want to spend time and money just making sure that the cables keep sending traffic. Passive Optical Network (PON) addresses this issue by removing all active components from the cable plant. The only active components are at the central office and the user抯 premises.
Introducing EPONczw光波通信
EPON consists of three generations of technology: 1G, 2.5G and 10G. The 1G generation of EPON was first deployed in 2004, while the 2.5G generation is being rolled out this year (2008). 10G EPON is the next generation of EPON technology and is slated for initial deployment in 2010. czw光波通信
czw光波通信
The 10G generation has two variants: asymmetric and symmetric. The asymmetric variant pairs a 10G downstream with the same 1G upstream that is used in the 1G generation of EPON. The symmetric variant of 10G uses 10 Gbps in both the downstream and upstream.
The Future of Internet Trafficczw光波通信
Cisco, in its white paper 揂pproaching the Zettabyte Era , presents its predictions for the general trends in Internet traffic out through 2012. Some of its main conclusions are highly pertinent to this article:czw光波通信
揑nternet video is now approximately one-quarter of all consumer Internet traffic”czw光波通信
czw光波通信
“The sum of all forms of video (TV, VoD, Internet, and P2P) will account for close to 90 percent of consumer traffic by 2012”czw光波通信
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czw光波通信
Table 1: Characteristics of the three waves of Internet trafficczw光波通信
czw光波通信
揧ouTube is just the beginning. Online video will experience three waves of growth.”czw光波通信
揤ideo communications and dynamic video content will ultimately test the Internet more than pre-recorded video content.”czw光波通信
czw光波通信
Cisco predicts that Internet video will be the dominant factor in driving traffic growth and network requirements. Both the volume and the nature of such Internet video traffic will change over time, falling into three waves of traffic growth (table1).
The Carriers Perspectiveczw光波通信
Carriers have two basic issues with which they constantly struggle: how to generate more revenue, while at the same time keeping costs down. On the revenue side, traffic management and QoS are the keys to enhancing revenue streams. On the cost side, the network needs to support upgrades in both the number of users and bandwidth without requiring costly upgrades to the fiber plant, forklift upgrades to central office equipment or replacement of already deployed Customer Premises.czw光波通信
czw光波通信
In order to keep costs low, carriers require that the network equipment at both the central office and user premises is as cheap as possible. Of equal importance is the cost of maintaining and upgrading the network over time. In particular, carriers are mandating that networks must support co-existence. In this context, co-existence means that the network must be able to support a mix of older and newer generations of network equipment, without the need to deploy new network infrastructure. In an Access Network the user terminals are deployed at user抯 homes or businesses. At any given point in time there can be millions of such Customer Premises Equipment (CPE) terminals deployed. Upgrading or replacing such CPE抯 is impractical due to the expense. Newer generation CPE抯 with higher performance must be deployable without requiring a new fiber plant. Thus the requirement is that old- and new-generation CPE抯 must be able to co-exist on the same physical fiber plant.
EPON Meets Market and Carrier Requirementsczw光波通信
The three generations of EPON technology are an excellent match for the requirements outlined in Cisco抯 three waves. The current 1G EPON maps to Wave1 (Internet Video to PC). The transition into Wave2 (Internet Video to TV) will see an increase in the number of channels, a switch from standard definition to high definition (HD) and an increase in Video-on-Demand (VoD). All of these Wave2 services are asymmetric, and will be well served by 2.5G and 10G Asymmetric EPON. These Wave2 services will scale up gradually over time and are extremely cost-sensitive. Having both 2.5G and 10G EPON at different price points will allow carriers to naturally scale their network capacity to match their service offerings. czw光波通信
Finally, Wave 3 (Video Communications) will require the network to be upgraded to support high-bandwidth symmetric traffic, which will be provided by 10G Symmetric EPON. In the early phases, this transition will most likely be driven by business users, who are less cost-sensitive and will be the early adopters of such communications services. Because EPON networks support co-existence, this business services early rollout will share the fibers in place for existing residential users, thus reducing rollout costs. Carriers will finally be able to start offering enhanced symmetric services to residential users, such as a web server hosted from a home office, or telecommuting with full support for virtual collaboration.
Convergence at 10Gczw光波通信
There are two main flavors of PON technology: EPON and GPON. EPON and GPON are incompatible in the current 1G and 2.5G generations. EPON and GPON currently use very different physical layers, which leads to incompatible chips, hardware and optical modules. czw光波通信
czw光波通信
In the 10G generation, the ITU and IEEE are discussing a plan for convergence of their specifications at the physical layer. This 揷o-opetition between GPON and EPON would allow for commonality of the chips, optics and hardware platforms, thus driving costs even lower. The differences between EPON and GPON would then be limited to the higher layers, which are typically implemented in software. Carriers would still have a choice of technologies in 10G PON, but would have the advantages of a single physical layer.
Summaryczw光波通信
Over the next few years Access Networks will undergo a transformation, with new services such as video distribution and video communications pushing the requirements for bandwidth and traffic management ever higher. Carriers face a daunting task: they must be able to deliver the Access Networks that support this roadmap while keeping their upgrade costs low and generating new revenue streams from these new services. czw光波通信
czw光波通信
Current access network technologies such as Cable and DSL are reaching their limits in terms of bandwidth and upgradeability. Other approaches such as point-to-point links are far too expensive to achieve the price points necessary for mass deployment. As we have discussed in this white paper, Passive Optical Networking (PON) is the technology that is best able to meet all the requirements of carriers now and into the future. czw光波通信
czw光波通信
The three generations of EPON are ideally suited to support the three waves of Internet usage as predicted in Cisco抯 Visual Networking Index roadmap. By supporting seamless co-existence of technology generations, EPON provide carriers with a cost-effective means to scale their access networks to match the needs of their markets. EPON is the technology that will enable the future for the last mile.
