Eliminating the access network choke point
Pressure on network and cable operators is escalating as new competitors enter the market and subscribers demand more applications and interactive services. Advances in Wide Area Network (WAN) technology are leading to huge bandwidth increases, a cost-per-bit that is quickly approaching zero, and content that can be virtually anything, and come from just about anywhere. In addition, enablers such as memory, processor power and wireless technology are leading to surging consumer demand for capabilities such as multimedia, home networks and separate access points.
It used to be that networks could get the additional bandwidth they needed by using fiber technology. But today there's a bandwidth "choke point" developing between the WAN and the consumer that is making it impossible for consumers to take advantage of the capabilities and applications that network and cable operators can offer—and simply adding fiber can't fix it. It's at this point in the access network that today's bandwidth battles are likely to be won or lost.The enablers: New optical electronics
A new generation of carrier-class optical electronics is providing cable operators with the enablers for a network architecture that will help them open the access bottleneck, win the bandwidth battle and give their subscribers the interactive applications and performance they want. The goal is to provide individual subscribers with access to more bandwidth, and the best, most efficient way to do this is to drive fiber deeper into the network.
Fiber deeper in the network means that fewer people are hanging off each piece of cable, so each subscriber can have access to more bandwidth and a higher-speed pipe. It also means less coaxial cable and fewer RF amplifiers, which leads to reduced equipment, installation and maintenance expenses.
Next-generation optical electronics are the enablers for a new network architectural approach that delivers carrier-class performance, functionality and features reliably and cost-effectively.
Most optical platforms available today were designed to operate in climate-controlled indoor environments. As a result, they lack the inherent environmental and user features necessary for successful deployment in harsh outdoor, and sometimes remote, locations. Driving fiber deeper requires that the optical platform be designed from the ground up for installation in a variety of locations, including field sites remote from the central office or hub, as well as indoor facilities. These new platforms must be easy to install and maintain, must operate reliably in a wide variety of environments, and must not require additional real estate.
Connections accessible from the front, a variety of mounting options, electronics that can tolerate temperature extremes, and remote management capabilities that allow maintenance and provisioning from a central site are among the features you should expect to find in optical platforms for fiber deeper deployments.
Among the inhibitors to providing substantial bandwidth to individual subscribers has been the expense of doing so. Fiber-deep deployments provide added bandwidth to individuals, but also mean a network must have more nodes and more available light, which in turn has usually meant higher costs.
A new generation of optical amplifiers is now making it possible to deliver more optical light than Erbium-Doped Fiber Amplifiers (EDFAs), at a fraction of the cost. With a cladding pump, for example, the typical $300 per-milliwatt (MW) cost for light via EDFAs plunges to just $45 to $50 per MW.
In addition to dramatically lower costs, the higher-power light these new amplifiers deliver provides some other important benefits. Specifically, it can send signals between buildings or from a single point greater distances, and allows networks to be constructed with conversion points placed deeper in the network, both of which contribute to eliminating the current network choke point and solving the last-mile dilemma.More reverse path bandwidth
New digital reverse capabilities deliver more return path spectrum, bring back more bandwidth at a lower cost, and stretch reach. With more reverse bandwidth available, the network becomes more symmetrical and makes true bi-directional capabilities a reality.
Baseband digital reverse was a significant breakthrough in bi-directional throughput. Now in its third generation, this technology has already increased throughput by a factor of six, which in turn has resulted in a 50 percent reduction in cost-per-fiber and measurably better performance.More wavelengths on a single fiber
Improvements in optical filtering in Dense Wavelength Division Multiplexing (DWDM) and 1550 MHz transmission products are making it possible to significantly increase the number of wavelengths on a single fiber. With DWDM and 1550 MHz products, a single fiber can now carry as many as 24 wavelengths, three times the traditional number.
More wavelengths per fiber translate to more interactive services on the downstream path. With 24 wavelengths in a single fiber, the number of interactive channels—unique interactive services—that can be delivered over a single fiber increases by a factor of four.Eliminating the access choke point
With the emergence of these new-generation optical electronics, the stage is set for a new architectural approach that will allow cable and network operators to overcome the last-mile dilemma and provide more bandwidth to individual subscribers by moving fiber closer to the home. The solution that makes this a reality is a carrier-class optical network that combines "third ring" architecture and equipment specifically designed for location virtually anywhere (See Figure 1).
The third ring in the new architectural approach can be categorized as a remote terminal (RT) deployment. Third ring architecture is actually a "ring-in-ring" topology that provides an optical path with cross ties. Cross ties reduce fiber requirements and provide backup paths that act as alternate routes back to a central office or hub in the event of a failure, thus limiting the number of subscribers affected.
The third ring architecture offers several distinct advantages over traditional architectural approaches:
- Serve more users with less fiber, fewer amplifiers. In a typical implementation today, parallel fiber runs from a hub or office in a point-to-point arrangement. Each fiber in this arrangement usually requires four amplifiers, and about 20 amplifiers are generally needed to service a 500-home area. In a third ring implementation, cascades will typically contain only one or two amplifiers, and because amplification levels can be higher, a network can actually feed more homes with fewer amplifiers. The net result is approximately 50 percent fewer amplifiers, lower power requirements, easier craft skills and fewer users per fiber, which translates to more bandwidth available for individual subscribers. In addition, operators can pull fewer fibers to an RT than they would have had to pull from an office.
- Extend reach, significantly reduce real estate and construction requirements. Today, in order to serve a 500-home area, it would be necessary to use three transmitters with a reach of five to six miles from the hub or office. To reach homes beyond that distance, another hub building would be needed, and so on. The third ring architecture can take advantage of 1550 nm transmitters that, unlike 1310 nm transmitters, can be amplified easily to extend reach to 83,000 feet—two to three times the reach of traditional technology. Depending on the geography of the area being served, it is possible that a building serving 20,000 subscribers can become a building serving 50,000 to 60,000 subscribers. In this scenario, a single hub can cover the ground that would have required three hubs in a traditional architecture, and that translates to significant real estate and construction savings.
- Expand and rebuild without dramatic service interruptions. Unlike traditional architectures that require running new fiber back to a central office or adding a hub building to accommodate internal and perimeter hub service area growth, third ring architecture and new-generation optical electronics make it possible to extend fiber from the remote terminal ring to the new locations. This means shorter fiber runs, no new buildings and less disruption to existing service.
- Reduce the impact of outages. As the ring-in-ring architecture drives fiber deeper into the network, its backup path provides a second route back to the hub or central office, eliminating the widespread outages that can occur in traditional topologies. The end result is that when outages occur in a third ring system, they are localized and affect fewer people
- Eliminate the need to incur expenses now to accommodate future growth. To contain costs in traditional fiber optic deployments, network and cable operators may lay dark (inactive) fiber to provide capacity to accommodate anticipated future growth. Unfortunately, in most geographies it is difficult, if not impossible, to anticipate what and where the needs will be far enough into the future to meet them accurately. The result is that systems will most likely need to add fiber, and possibly hub buildings as well, to accommodate actual growth.
In a third ring architecture, fiber costs can be managed more effectively, because fiber can be extended starting from the RT ring, eliminating the need for long fiber runs back to a central office or a hub. With the optical electronics and the cabinets that contain them designed for outdoor deployment and about the size of a small file cabinet, they can be located virtually anywhere, further simplifying the task of adding capacity wherever it is needed to accommodate new subscribers and expanded requirements.
- Combine broadcast and narrowcast signals, then direct them to individual nodes. The ability to accommodate more wavelengths on a single fiber makes it possible to combine broadcast and narrowcast signals and direct them to individual nodes. Different wavelengths are sent to each node, which means that two fibers can "talk" to multiple nodes (eight in the example) with what look like different signals. This capability also makes it possible to combine commercial and residential signals on the same fiber without risking one interfering with the other.
The flexibility of the third ring architectural approach addresses key network drivers such as reusable bandwidth per user and interactive connection capacity. It is a solution that provides extended reach, minimizes the need for hub deployments, and makes accommodating new and changing subscriber requirements faster, easier and more cost-effective than with traditional approaches.
Most significantly, it provides a solution to the last-mile dilemma, effectively eliminating the access network choke point that is keeping today's subscribers from taking advantage of emerging services and applications, and today's cable operators from reaping the financial benefits that offering these services can deliver.Conclusion
One of the biggest challenges network and cable operators face is bandwidth; specifically, how to add enough highly reliable capacity cost-effectively to meet a growing demand for interactive services. Now, a new Remote Terminal network architecture takes advantage of the strengths of traditional carrier access networks, but delivers many times more bandwidth per subscriber to better support current and future interactive IP-based applications.
Coupled with a new generation of optical electronics designed to provide carrier class performance, functionality and features, this new network architectural approach can provide an effective solution to the bandwidth issue.