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October 2000 Issue
Planning 2001: Designing Tomorrow’s Headends
Planning for the road ahead
By and

Keeping up with today’s demand for two-way, interactive services is a daunting task for any cable operator. So how do you also ensure your system is equipped to keep up with tomorrow’s new technology challenges? ADC offers its strategies in the first of a two-part series.

Just a few years ago, no one knew about running modems over broadband for Internet surfing. Today, in addition to cable modems, there is an incredible push for digital video, telephony and countless other interactive services. Subscribers have become more discriminating, with higher expectations for reliability, accessibility and response time.

Planning for tomorrow will be more complex

Within the turbulent networking environment, planning for the future has become increasingly more difficult. Most operators are already pushing the envelope in terms of capacity and services in keeping their networks up to date, much less being able to predict what’s going to develop.

In the past, making changes was easy when the only service delivered was video. Little consideration was given to how subsequent changes would affect delivery of new services. When adding channels, operators had the luxury of preparing the headend for the changes, implementing them during periods of low viewership. Customers typically didn’t notice the interruption.

Capacity was easy to figure out, too. Delivering video signals was almost "one-size-fits-all." A video signal was generated, split and distributed to where it needed to go. Operators didn’t have to worry about how many customers were served because it was just a matter of reamplifying signals.

Competition is the driver

Today, the window of delivering services is rapidly shrinking while the complexity is magnified. The primary driver is competition. Cable operators are no longer the only game in town, with phone companies now delivering DSL. Overbuilders are claiming they can do things better. To compete, cable operators are being deluged with new initiatives, but are also expected to implement them smoothly and quickly.

A common headend upgrade scenario today has operators adding telephony or data services to their existing video network. Unlike video equipment, cable-modem and telephony equipment typically have some capacity limitations, and quality of service (QoS) associated with a specific number of customers. If you exceed that QoS limit, signals will begin to degrade or not work at all. This is, of course, unacceptable to customers.

Design for today... or tomorrow?

As they design their headends, operators face a "Catch-22" situation. They can either design equipment for what is initially most cost-effective, or for when the network has grown and services are fully deployed. Though designing a network for initial take-rates is more cost-effective, operators eventually will have to add on as services ramp up. On the other hand, if they design it for a higher-take rate scenario, they invest in a lot of equipment under the assumption that services are going to be successful. It may be difficult to predict take rates, and an operator doesn’t want to deploy a full-blown system with only a few customers. Right now, most operators feel confident cable modems are going to be very successful, but they are still adopting a "wait-and-see" attitude when it comes to equipment purchases for the long term.

Modular components a must

Implications for the headend mean the passive and active components deployed must be modular and flexible. These components must perform adequately today and be useful for future requirements.

Historically, the splitter/combiner function used discrete, non-specialized components inserted in the back of an equipment cabinet or haphazardly mounted on the wall. Although functional, this approach was very inflexible, connections were difficult to access, and it took up a lot of real estate in the headend. Functions such as padding or monitoring were not built in to those products. To perform those functions, operators had to use inline pads or devise a customized way to monitor the signal.

Vendors today have an eye on the future and are offering more functionality in modular, compact packages that plug and play into a flexible chassis. With space at a premium in most headends, the high-density nature of these components preserves valuable real estate. Plug-in modules allow operators to configure networks with different functional module types in the same chassis, or add additional splitters/combiners, as dictated by network expansion. For example, an operator can buy an empty chassis and initially add just a few modules. An empty chassis that holds 14 cards is a lot less expensive than buying 14 cards worth of equipment. And there is room to accommodate network expansion without having to worry about reconfiguring an entire rack of equipment. A service addition or service area expansion becomes a simple matter of inserting a new module into an existing chassis.

Support costs

With reliability issues paramount, network planners should not make financial decisions simply by comparing product prices. Component cost is often insignificant compared to the less predictable costs of support and customer impact. Support costs are important for two reasons. First, support is a continuing process. A component is bought once, but must be maintained for life. Second, support costs are not fixed. The tightening labor market continues to drive up the cost of support as it is becomes harder and harder to retain skilled labor. The rate of increase in technical labor costs far exceeds today’s moderate rate of inflation, so it makes sense to pay a little more for reliable, technologically superior products that help reduce support costs and the potential damage network problems can cause customer relationships.

Managing many signals

Another big consideration for operators is the amount of return path bandwidth from an optical node serving area. The return path is a very narrow piece (5 Mhz to 40 Mhz) of the overall RF spectrum. Because of that, as these usages go up, the spectrum quickly becomes congested. Operators are shrinking node sizes so they have fewer customers using the same amount of return bandwidth. Although this effectively delivers more bandwidth per customer, it also increases the number of serving areas sending signals back to the headend.

Operators now must also consider how to manage all the signals coming back from the field. With added equipment, today’s "mega-headends" have more cables running through them, which will only increase and become more complicated with the passage of time and the addition of new services. But how are signals going to be redistributed to this equipment? If they are all bundled together, finding a particular cable or tracing a particular signal may be difficult and time consuming. Haphazardly running cables through the headend could result in unintended service outages. Therefore, it is essential to have a cable management system in place that is well organized, easy to understand and able to protect the cables from damage.

Troubleshooting and testing

Troubleshooting too has become—and will continue to become—much more complex, placing new demands on signal management equipment. Most systems employ a chief headend technician who knows everything about how the headend was built and how it operates. In the headend of the future with more services and divisions, this function has become much more segmented and specialized. Big operators may have separate organizations for video, digital video, telephony and data. Each of these groups is responsible for its own services, but uses the common broadband pipe to deliver them.

From an organizational perspective, it has become imperative to understand where each of the signals are and to have specific test points for each. If you had a video problem in the past, you would just disconnect the feed and check it out. Now if a video technician does that, depending on the location on the network, he may take down the cable modem and telephony service, again causing customer dissatisfaction. With such an increase in new service applications and the dynamic nature of take rates for all services, the need to quickly and effectively balance signal levels becomes even more imperative.

To address this, many signal management modules have built-in test points, and non-intrusive testing to scrutinize signals passing through the module. This testing can be done without taking down any of the services, and allows technicians to monitor bit error rate information and other valuable data.

Return paths

Return paths also place an additional requirement for test points. Traditionally, the return paths were not used for much other than low data rates and narrow bandwidth services, such as status monitoring or set-top control. The return path generally didn’t touch the customer. In today’s and tomorrow’s networking environment, thousands of subscribers are using cable modems that do not function without using the return path. Because of the limited bandwidth and frequency spectrum it occupies, return path ingress becomes a huge issue. When services are combined together and take rates grow, unacceptable ingress could affect a number of serving areas making it critical to be able to go into the headend or hub and monitor that signal, looking for noisy nodes and noisy serving areas.

No one knows for sure where today’s networks are heading. What is known is that modular platforms that allow flexible network reconfiguration will be essential in supporting the expanded services and growth, along with different testing and troubleshooting functions unique to interactive, two-way networks. Without building flexibility into the design, today’s new headends could turn into tomorrow’s expensive nightmare.

Sara Manderfield is the RF signal management product manager for ADC. She can be reached at . Ross Ruschmeyer is ADC’s senior project systems engineer. He can be reached at .

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