IP networks now and forever: Carriers must bridge packet, circuit-switched networks

The fervor surrounding next generation networks is taking the industry by storm. Many competitive local exchange carriers and interexchange carriers are banking on Internet protocol networks.

Because so much of today's traffic is IP-based, carriers are building networks that are optimized for packet transmission, said Aman Kapoor, director of switching and routing at Ryan Hankin Kent. "[W]hen you log into the network, from home or from work, the traffic that is carried is IP," he said. "You need bigger pipes in the core of the network to carry the traffic and satisfy demand."

Qwest Communications, PSINet, IXC Communications and Level 3 Communications all have built IP networks, and Frontier and WorldPort are hot on their heels. PSINet built a fiber link connecting New York, Chicago, Dallas and Los Angeles that runs IP over OC-48 (2.5 Gb/s). Frontier is deploying IP over a nationwide OC-48c network that will eventually connect 120 markets. It will operate directly over the Optronics dense wavelength division multiplexing network.

To deploy an IP network, service providers must bridge the packet and circuit-switched networks. Level 3's IP Device Control gateway does just that by connecting the public network to IP-based networks, explained Ike Elliott, senior director of voice network engineering at Level 3.

Under the umbrella of the Technical Advisory Council, a group of 12 data communications and telecom equipment suppliers developed the standards-based gateway (see figure). It boils down a circuit switch into its pieces: a controller and any number of line cards, Elliott said.

"The IPDC does not directly interact with the circuit-switched network," he said. "The IPDC lets us take the controller and separate it from the line card, and put it on different edges of the IP network. The line cards are the media gateways, and the gateway converts a telephony call into IP calls. The controller is deciding where to route the call. It is telling the gateway what to do."

Although these carriers lead the pack, others are still ramping up to IP. WorldPort is deploying a global IP network in a three-phased approach encompassing collocation, integration and migration, said Jim Hendrickson, vice president of technology and strategic planning.

Using Lucent Technologies equipment, WorldPort is collocating IP switches and IP telephony equipment with the circuit-switched equipment, then multiplexing the two protocols over the backbone, Hendrickson explained.

WorldPort is moving to IP "to drive the cost out of transmission and telephony and telephony services [and to] gain the cost efficiencies that are inherent in a packet network," Hendrickson said.

But is it premature to bet on IP? The major drawback has been quality of service, something asynchronous transfer mode handles well. Some organizations are working on class-of-service standards for IP. IP also has less overhead and costs less per bit, which is apparently enough to keep carriers in the IP game.

Nine months ago, Hendrickson would have bet on ATM, but that has changed, he said. "When you take out the thinking of voice over IP, and when you're using IP as the underlying protocol for voice, then it's a clean answer, he said. "[IP] is a well-understood, universal and ubiquitous protocol that is easy to support, easy to write to and easy to develop products for. ATM is mired in the attempt to be all things to all people."

While Kapoor acknowledged that the IP vs. ATM debate will rage on, he said that vendors and carriers are moving forward. "There is a strong need today for higher-speed IP connections, higher than OC-48," he said.

DIRECT TO YOU Ericsson has built optical layer protection into its Erion dense wavelength division multiplexing systems. An alternative to Sonet protection, the systems enable ATM, IP and Ethernet traffic to travel directly over DWDM.

INTERNATIONAL MULTIPLEXING Adtran has introduced the ESU 120e multiplexer, the first in a series of E-1 network termination devices targeting the international market. The multiplexer combines voice and data on a single E-1 circuit and has an expansion slot that can support multiple applications.