Verizon begins shift to packet-based voice calls

Telecommunications service provider Verizon Communications Inc. has begun using an ATM (Asynchronous Transfer Mode) backbone to carry some voice calls, the first step in the carrier’s first migration to a new switching technology in approximately 30 years.

Setting up gateways between Verizon’s traditional circuit-switched network and its ATM backbone, which previously had been used only for data traffic, kicks off a move toward IP (Internet Protocol) telephony that should lead to lower costs and a more resilient network, as well as integrated voice and data services, according to Phil Harrington, Verizon VTOA (voice trunking over ATM) Program Manager.

Traditional voice networks use a specific, “nailed-down” circuit over a certain path for each call. Calls carried over an ATM or IP network are broken down into cells or packets, which can more easily be sent over different paths depending on current capacity and bottlenecks. Those cells or packets can also be mixed with data to make more efficient use of a single network. Cell and packet networks generally are less expensive to build and are easier to expand with just the capacity that is needed.

Verizon, based in New York, set up Nortel Networks Corp. Multiservice Gateway 4000 devices in interoffice facility hubs in Newark, New Jersey, and Tampa, Florida, to convert calls to ATM cells and put them on the ATM backbone. Trunks carrying calls from multiple central offices go into the hubs. The network also uses Nortel Succession Communication Server 2000 packet-based voice switches and Passport 15000 Multiservice Switches for ATM transport, according to Verizon.

The carrier is already using the system for some of its own internal management calls and in Florida is using the ATM network to carry some voice calls from third-party users of its network, which include competitive local exchange carriers, mobile phone operators and other kinds of service providers.

Verizon additionally plans to use the ATM backbone for Verizon customers’ calls when they overflow the capacity of regular switches. These usually amount to 10 percent to 20 percent of calls and so far have been carried over supplemental circuit switches. Legally, the carrier can’t put its own overflow on the ATM network until it has made voice trunking over ATM available to other service providers, Harrington said.

Shifting of voice calls on to the ATM network will be transparent to end customers, Harrington said. The service will be rolled out in several other locations over the next 18 months, according to a Verizon statement.

Upgrades and new products from Nortel will allow Verizon to shift calls from the circuit-switched network to a packet or cell network closer to the end user, and to convert the voice traffic to IP packets instead of ATM cells. Those elements should be available by the end of 2004, he said.

“IP is where we want to go,” Harrington said. That move would put the phone network on the same protocol as the Internet and could open the door to a new generation of services that combine Web-based data with voice calls.

However, Harrington said he isn’t convinced IP is ready for the job. ATM was built from the ground up to deliver information, such as each word a caller speaks, in the right order and at the right time; IP was designed for a “best-effort” approach.

“We know ATM provides the quality of service required for carrier-class (networks). IP isn’t there at this point,” Harrington said.

Verizon currently is talking to vendors about testing voice calls on IP using the emerging mechanism of MPLS (Multiprotocol Label Switching), he said.

A Verizon team first began studying a move to packet switching in 1998 and chose Nortel as its vendor in late 1999, he said. Making it happen took a long time because the carrier had to devise new methods and procedures for monitoring and administering the new type of network, and make its existing software work with the new system.

“This is the first time in 30 years we’ve moved to a next-generation switching architecture,” Harrington said. The last such migration took place in the 1970s, when carriers converted from crossbar electromechanical switches to digital switches.