As data and video traffic grow, so too must an operator’s optical backbone.

Capital costs can be significant, but an integrated network can reduce overall costs and greatly simplify management and the deployment of new services. Reconfigurable optical add/drop multiplexers (ROADMs) are playing an important role in these upgrades.

Last December, Cox completed a yearlong project to completely overhaul its backbone. Although the main purpose was to improve the infrastructure for carrying cable modem traffic, Cox found an architecture that promises to support cell phone backhaul and new business services.

More logical routes
Before the project started, Cox was using a mishmash of leased circuits from different providers across the country. This created a logical nightmare, noted Mark Pellegri, Manager of Transport Networks at Cox.

In many cases, the shortest or most direct routes were not the most economical. These routes were more expensive because there were not as many service providers to choose from, or they did not like providing traffic to certain markets.

For example, it cost less to send traffic via intermediate cities rather than a straight shot between two cities. A lot of the traffic that needed to go to Orange County, California, had to pass through Los Angeles or San Diego first.

“Now with our own physical backbone we can route directly without having to think about economics,” Pellegri said.

The network spans about 14,000 route miles between 26 cities. Twenty of these are in Cox markets, while the other six are in peering centers operated by either Equinix or Switch and Data. The common infrastructure for the network is 10 Gigabit Ethernet. The backbone includes dark fiber, making it easier to upgrade.

Easy turn up
Cox built the network using digital ROADMs from Infinera. This equipment in turn uses Generalized Multi-Protocol Label Switching (GMPLS), a control plane technology that allows an engineer to route a service through the network without any manual provisioning. Furthermore, it supports advanced protection schemes over the network mesh rather than needing a dedicated backup line for each circuit.

Pellegri said that network reconfigurability works as expected, and makes it easy to turn up new circuits and wavelengths. When a new service is requested, there is no new engineering that has to be done in terms of finding shelves for the cards.

One of the features of Infinera’s ROADMs is their ability to convert and process each optical signal electronically at every hop in the network. An engineer only has to ensure there is enough optical power for a single hop instead of worrying about the link budget for a longer connection.

“It has been a godsend,” Pellegri said. “You don’t need anything more than a spreadsheet to do capacity planning and budgeting. That would not have been the case with other technology.”

In the past Cox had to do complex calculations on whether the wavelengths were available on a given node and the optical characteristics of the fiber across the length of a link between two cities. Even if they figured it out, the pricing offered by the long distance carriers for a particular link could change by as much as three times.

Pellegri said those variables required “risk hedging” when making a budget.

Such operational costs have become too big to ignore. “Operators came to the conclusion that the networks had become far too complex, which means they needed to put more intelligence into the network,” Gaylord Hart, Infinera director of MSO market segments said.

“We have seen a shift towards a focus on the total cost of ownership which includes everything from the CapEx to the growth of the bandwidth,” Hart said.

ROADM costs, benefits
But this level of automation is not for the faint of heart, said Scott Wilkinson, vice president of Hitachi Telecom.

Network operators are nervous about that amount of bandwidth being reconfigured on its own, he said. They want to know what happens when a circuit breaks and how it will be restored. Also, while ROADMs promise to reduce costs, the benefits are not easy for all to obtain.

“The reason most service providers cannot do this now is because they have not upgraded their whole network. ROADM generally requires a new network,“ Wilkinson said.

There remains plenty of SONET-based networks. But as demand for speed grows from 10 to 40 to 100Gbps and high-bandwidth services expand, backbones will need to adjust as well.

“The telcos and operators have taken advantage of the fact that data usages is not simultaneous,” Wilkinson said. “Now they are seeing that the backbone is the same way. They are looking at combining ROADMs and other things to get even more out of the network.” 

—George Lawton

The Daily


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