Cox Communications and its primary vendor, Nortel Networks, have detailed plans to convert Cox's local telephone service from traditional circuit-switching to voice over IP, beginning immediately. The cable company, which was most aggressive in deploying circuit-switched telephony networks, is now upgrading those circuit switches to be hybrid, capable of supporting VoIP as well. The changeover involves a classic "cap and grow" strategy that will put new Cox telephony customers on a lower-cost softswitch/media gateway network, while supporting existing customers on the TDM network Cox already built, based on Nortel switches.

Cox was the cable industry leader in building circuit-switched voice networks, beginning in the mid-1990s. As it begins VoIP deployment, Cox has 1.2 million residential customers and 100,000 business sites in 17 markets in its network. The company has already deployed VoIP as a long-distance transport strategy in five "greenfield" markets.

But there is a strong economic driver for growth in existing TDM markets to be VoIP-based as well, said Jay Rolls, vice president of Telephone and Data Engineering at Cox.

"The economic drivers are pretty strong," he said. "With a lot of our services, the most price-sensitive aspect is what has to go into the home itself."

For its existing telephony service, Cox uses proprietary gear from Arris as its CPE while with VoIP it can use standardized media terminal adapters that are less expensive, given the economies of scale.

Cox began deploying VoIP in Roanoke, Va., in December of 2003, and has spent the last year "getting our comfort level," and launching the four other new markets, Rolls said. After doing extensive modeling, the company decided it would be more cost effective to evolve its existing Nortel switches to hybrid TM/VoIP systems, instead of building a VoIP overlay. Cox will upgrade at least 10 Nortel DMS switches to Nortel Communication Server 2000 hybrids, to serve more than 50% of its new growth lines on VoIP by the end of the year.

"As we worked with Nortel, they put in front of us a method and a migration strategy that made it work," he commented. "The hybrid approach means we could go six months with VoIP and go back to TDM--not that we'll do that. But it's important because you don't have to run two totally stovepipe systems side by side."

Serving all voice customers on a single system simplifies the process of customer support, as well. The new VoIP service will automatically be connected as part of the existing voice network, including signaling system 7, data management telemetry and E911 connections.

"All that is in place today and we can leverage it, which should allow for a faster rollout," Rolls said.

In addition, Rolls said, the softswitches can be regionally deployed, which means greater flexibility in deployment as well as savings. Cox can add markets in areas where it has deployed the hybrid Nortel solution by adding additional Nuera Communications BTX media gateways.

"With VoIP, the notion of geography starts to fade away," Rolls said. "For example, if we upgrade one of the switches in Orange County for Santa Barbara, where we haven't launched telephony, we wouldn't put a softswitch in Santa Barbara, we would launch off one of these hybrids that is already deployed."

Using VoIP will give Cox the flexibility it needs to support a new generation of voice services, including Integrated Messaging, he said. The flexible architecture will also give Cox the opportunity to expand its service territory more easily, said Elaine Smiles, director of cable marketing for Nortel.

"That's another advantage of VoIP--not only is it more cost-effective on the access side, but the architecture is so different," she said. "You can not only leverage the switch for the immediate community but go out of territory. The installed base becomes quite large, and as it grows, you can choose to put a softswitch closer to where the subscribers are."

Cox is determined to provide VoIP service that is no different in quality from its TDM voice, said Rolls. For example, Cox VoIP will meet E911 and CALEA requirements from the outset, and comes with a battery backup system that provides eight to 10 hours of service when commercial power goes out.

"There is a device in the home that is the registered access point of the user," said Smiles. "Even though traffic is traveling on VoIP, there is a registered device that says where that location is, for E911 purposes."