February 2001

BY GARY ROGERS

Circuit switching was the foundation of the Public-Switched Telephone Network (PSTN) for the first 100 years of its existence. Over the past few years, however, this foundation has been challenged by new technology hearkening from the world of data networking. Today it seems clear that the telecommunications industry is evolving to a packet-based network architecture that supports both voice and data services. Carriers are eager to make the transition to the new converged network.

As the voice network evolves, service providers face the issue of how to best implement the new technologies being introduced, while continuing to fully leverage their existing infrastructure. The approach taken by many service providers is a "cap and grow" strategy, where voice over packet solutions are integrated into, and will eventually supplant, the existing circuit-switched network. This approach allows carriers to achieve several objectives:

• Retain legacy connectivity to the PSTN by black phone;
• Leverage investments in existing equipment and service platforms;
• Offload data traffic from congested voice networks; and
• Utilize new access technologies such as cable, DSL, wireless and others.

Beyond the infrastructure benefits described above, packet telephony also delivers extremely compelling economics. Packet telephony allows carriers to significantly reduce their acquisition costs, as well as the ongoing costs involved in operating the network, such as real estate expenditures and environmental costs (power, cooling, etc.). However, as carriers are quickly recognizing, packet telephony's greatest impact lies in its ability to facilitate the rapid creation and deployment of profitable new services, something that is virtually impossible in a circuit-switched architecture.

Making The Transition
Carriers clearly understand the considerable benefits that are to be gained by deploying a next-generation packet voice infrastructure. The challenge facing carriers is how to make the transition to the packet voice network as seamless as possible. Subscribers expect a certain level of functionality, as well as the extremely high reliability and quality of service that have been a hallmark of the PSTN. Therefore, carriers require a comprehensive packet voice solution that offers not only the highest levels of functionality and reliability, but also the scalability and manageability that will allow them to build extremely large voice networks. Additionally, it is crucial that the next-generation voice solutions integrate with carriers' existing operations support system (OSS) environments.

Most carriers have circuit switches that are not fully depreciated. Naturally, they wish to continue to use them, but would like to cap their investment -- it certainly makes no sense to continue to invest in yesterday's technology. Therefore, while migrating to packet, carriers must maintain a transparent and scalable bridge to the legacy equipment already deployed in their networks. The steps to a successful (and less-painful) migration are:

1. Install the packet voice solutions at the edge of the packet network.
2. Interconnect the packet voice media gateway switches and softswitches to the existing circuit switches and provide connectivity to existing SS7 networks. The media gateways can now handle calls routed to them from the circuit switches. No changes are required to the circuit switches -- to them, the new packet voice solutions appear as other circuit switches.
3. Route all new traffic to the media gateways. In this manner, the media gateways handle this new traffic, avoiding the need to deploy additional circuit switches.

With this infrastructure in place, traffic from circuit switches can gradually be rerouted to the packet voice network and the circuit switches removed, or redeployed for other purposes.

Services Provide The Competitive Advantage
One of the most compelling reasons to move to packet technology is the development of new applications and services that subscribers are willing to pay a premium for. These services create a true financial advantage for innovative carriers.

Packet telephony helps create new services that are difficult to develop when voice and data ride separate networks. In addition, packet telephony helps speed time-to-market for new applications because they can be developed on inexpensive, industry-standard platforms using commercially available tools. New services can be developed in-house or by third parties, depending on the needs and resources of the carrier.

The explosive growth of the Internet has also created a demand for services that bridge the worlds of telephony and data. These types of applications have been slow to develop, in part because of the separation of the two networks. Many analysts believe that network convergence will eliminate the barriers and yield a flood of innovative new services, most of which have not yet been imagined.

The Evolution Of The Packet Voice Network
Initially, packet telephony has been deployed by the market's early adopters, such as next-generation carriers, for use in trunking applications. In this application, the carrier introduces packet voice solutions into the core of the voice network, for a Class 4 or long-distance replacement. Using voice-over-packet, these carriers have built networks that deliver a range of traditional voice services, such as 1+ dialing, 800 number services, credit card calling, and others. Additionally, service providers have begun to introduce the next-generation applications enabled through the packet voice model. Examples of these services include unified communications, enhanced voice mail, click-to-talk, and presence management.

For the same sound business reasons that caused long-distance providers to make the technology shift to packet switching, access providers are now seeing the benefits of capping their investment in Class 5 circuit switching equipment. While the transition to packet switching by access providers -- those carriers who connect telephone subscribers into the core network -- has been happening at a much slower pace, there is significant activity in this segment. As a first step, many service providers, such as ISPs and CLECs, have begun to deploy packet voice solutions to ease the burden modem-generated Internet traffic is placing on their voice networks. In what is known as "Internet offload," service providers front-end their existing Class 5 circuit switches with a carrier-class media gateway. The media gateway is designed to transport modem calls destined for remote access servers and the Internet, diverting them away from over-taxed, expensive legacy circuit switches before they ever enter the voice network. Voice traffic may be switched back to already-deployed circuit switches, or alternatively handled by the media gateway switch itself.

As the market continues to evolve, carriers are beginning to build out the access portions of their network using voice-over-packet technologies. Service providers are starting to deploy networks that incorporate a number of new access technologies and devices such as DSL, cable, wireless, IP appliances, and residential and access gateways. In the packet voice architecture, calls can be routed between packet access devices or out to the PSTN through media gateway switches. Controlling this network is the softswitch, which handles all call routing, as well as providing all of the services formerly provided by the Class 5 switch. As in the long-distance portion of the network, packet telephony will enable access providers to deliver a range of new services not previously possible in the circuit network.

Changing The Way The World Communicates
The migration to the new public network presents an opportunity to fundamentally change the way the world communicates. With the convergence of voice and data in the new public network, carriers are now able to dramatically improve their business models. Packet telephony offers service providers considerable benefits over the circuit-switched environment of the past, including significantly enhanced economics and the ability to deliver new and inventive services that attract new customers and prevent churn in the existing customer base. However, it is recognized that carriers have made enormous investments in telecommunications equipment over a period of decades, and it is most practical and cost-effective for them to gradually migrate to packet voice networks while continuing to leverage their legacy systems. And, with packet telephony, service providers can now make a graceful transition from the circuit-switched networks of the past to the new public network. 

Gary Rogers is vice president of worldwide sales and marketing at Sonus Networks, providers of solutions that enable service providers to deploy an integrated network capable of carrying both voice and data traffic, and to deliver a range of innovative, new services. 

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Telecommunications companies of all types are making the gradual yet steady journey from the circuit-switched world to one where packet technologies reign. These leading-edge firms, ranging from local exchange carriers to global service providers, are beginning to recognize and quantify the substantial benefits of deploying next-generation packet voice networks. Through packet telephony, service providers gain the ability to drastically lower their operating costs, and most importantly, to create and offer new and profitable services to their subscribers.

Today, Global Crossing is furthest along in pioneering a full-scale, global migration from a legacy, circuit-switched network to a packet voice infrastructure. Global Crossing was the first carrier to publicly commit to deploying packet-based media gateways and softswitches as the core of its next-generation network. It has laid out an aggressive three-year strategy for moving all of its voice traffic over the IP network. This network will be fully integrated and capable of handling more than three billion minutes of traffic per month by its completion in 2002.

Early on, Global Crossing selected Sonus Networks to help build-out this groundbreaking VoIP network. The carrier is now deploying Sonus' complete Packet Telephony suite including the GSX9000 Open Services Switch, the PSX6000 SoftSwitch, and the SGX2000 SS7 Signaling Gateway throughout Europe, Asia, Central/Latin and South America. Sonus' integrated solution helps facilitate Global Crossing's evolution to a VoIP infrastructure, and will enable the carrier to offer traditional as well as new, enhanced services to its customers.

Sonus' GSX9000 gateway was designed from the ground up to meet the same stringent demands placed upon circuit switches in the past. Public carriers like Global Crossing also require the highest levels of interconnectivity, capacity, reliability, scalability, and voice quality in their VoIP central office switches. It is the GSX9000 that enables Global Crossing to further its VoIP expansion without negatively impacting any voice calls. Global Crossing is also deploying Sonus' PSX6000 SoftSwitch, a call management server that provides call control and intelligent routing functions. The third component of Sonus' Packet Telephony suite operating in Global Crossing's VoIP network is the SGX2000, which works in conjunction with the PSX6000 to provide critical SS7 voice services in the U.S. and in the international market.

All of these infrastructure solutions are based on Sonus' Open Services Architecture, a framework upon which carriers like Global Crossing may develop an unlimited number of new and innovative services. These services can be developed in-house or externally and, by taking advantage of the latest technologies, speed the time to market by weeks and sometimes years.

Global Crossing is now passing live traffic over the VoIP backbone in its domestic production network, a transition that has been seamless in execution. Sonus' solutions, underlying the packet network, have enabled Global Crossing to migrate voice traffic from its circuit switch network, completely transparent to its customers. Carrier termination type services will be available in seven European cities and the U.S. in the first quarter of 2001.

Over the next two years, all of Global Crossing's voice traffic will be transferred from the original circuit-switched network to the next-generation packet network using Sonus solutions. When it is completed in 2002, Global Crossing's network will span five continents. The global footprint will extend throughout North America, Europe, Asia, and South and Central America, and the VoIP network will be capable of handling more than three billion minutes of traffic per month.

Global Crossing is revolutionizing the communications industry by creating the first carrier-class, all-IP network. Sonus Networks is partnering closely with Global Crossing throughout the project to help build this landmark infrastructure. The end result will be a world-class VoIP network that creates new business opportunities for Global Crossing, reduces its operating costs, creates new revenue streams, and provides Global Crossing customers with innovative and profitable services. 

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