A natural progression

Both traditional service providers and emerging carriers view asynchronous transfer mode as the next generation technology that will help them drive revenues and contain costs as they compete in a continually complex marketplace. ATM has the potential to carry a wide range of traffic types--such as time division multiplexed transmissions and frame relay virtual circuits--that currently are transported over separate overlay networks.

While network consolidation has the potential to provide numerous operational benefits (Table 1), there are also opportunities for ATM-enabled carriers to offer customers new services by taking advantage of the technology's inherent ability to handle high-speed data, multimedia and video.

The transition from today's infrastructure into this core ATM infrastructure will not happen overnight. This transition will likely happen in multiple steps as the technology matures, each step further strengthening the move toward the next.

The first phase, which already has begun and will continue for about three years, focuses on providing advanced business, data and voice services with strong service differentiation. Next, over a five-year period, current services will be pushed toward a unified ATM core. Finally, an optimized core infrastructure will be capable of supporting mass markets with stronger interworking between narrowband and broadband services. However, this final phase is at least 10 years away.

The three-year view In the first phase of ATM deployment, many carriers will have an extensive ATM infrastructure that is driven largely by high-growth data service requirements. Most important, the ATM network will support a range of internetworking services, including both public Internet access and virtual private intranet connectivity. Many businesses need a network that supports different classes of services and supports firewalls between different services, even within an enterprise.

The distributed ATM backbone support frame relay and cell relay and will provide interworking between the two services. Carriers must allow businesses to maximize their existing investment in frame relay equipment by enabling them to access ATM-based services.

This ATM infrastructure also will provide transport for a range of custom broadband solutions for local area network interconnection and video networking. Core service switches will be deployed to provide backbone bandwidth between multiservice nodes(Figure 1).

While the majority of voice and private-line traffic will continue to be carried over entirely separate networks, carriers will begin to conduct field trials of ATM as a means of consolidating these separate networks between central offices.

A broad suite of technologies, including access concentrators for analog dial modem, ISDN and digital subscriber line (DSL) technologies from 128 kb/s to 1.5 Mb/s, will support access for internetworking services.

DSL access multiplexers (DSLAMs) also will be deployed, enabling ATM to operate end-to-end over an ADSL connection.

At this phase, the ATM network operates as an overlay to the interoffice Sonet infrastructure, primarily using integral OC-3 (155 Mb/s) and OC-12 (622 Mb/s) interfaces from the switches to the Sonet add/drop multiplexers (ADMs). Backbone route protection is enhanced by 1-to-N interface protection, which provides full backup in case one of the physical links is dropped, and by rerouting based on soft permanent virtual circuits

(S-PVCs). S-PVCs have characteristics of both permanent and switched virtual circuits (SVCs). In the case of a network failure, an S-PVC can reroute multiple virtual path and virtual circuit identifiers contained within a physical link, using SVC-like messaging capability (Figure 2).

This reduces network backup costs by eliminating the need to preprovision reroutes, and it provides immediate reroutes using all available routes.

Also during phase one, the circuit emulation capabilities of ATM switches are used in conjunction with private-line services to provide enhanced 3/1 and 1/0 circuit management across the ATM core. 3/1 circuit management involves mapping DS-1 (1.5 Mb/s) circuits into DS-3 (45 Mb/s) circuits, while 1/0 circuit management maps DS-0 (64 kb/s) circuits into DS-1 circuits (Figure 3).

This provides enhanced private-line services under the control of advanced service management capabilities. PBX trunking also is supported across this network. Initial trials of voice over ATM are now underway.

Advanced service management will become an important way to differentiate services, enabling carriers to offer high-performance statistics collection and billing systems and enhanced end user access for provisioning, monitoring service level agreements and obtaining billing information. For users, this means having an outsourced network for which they can obtain real-time service status and performance reporting. Standard interfaces to embedded operations support infrastructure are critical to support a service provider's billing and service delivery tools.

Five-year view In the five-year time frame, backbone switches and edge switch trunk interfaces will be widely deployed. There will have been a significant consolidation of first generation data networks into the integrated ATM platform, including frame relay and selected dial-in and DSL applications.

Network routing information will be centrally administered and ATM-based services will be able to take advantage of higher intelligence above the ATM layer (Figure 4). This intelligent network-like architecture will lend itself to the rapid creation of value-added services.

Call management functionality is currently available for voice service such as time-of-day call routing and will be available for multimedia calls. Carriers will begin to offer commercial voice-over-ATM service. There also will be opportunities in advanced data options for virtual private enterprise networks.

10- to 15-year view In the final phase of ATM deployment, virtually all interoffice traffic will be carried on the core ATM network, which commonly uses OC-192 (9.9 Gb/s) facilities. Sonet ADM capability will be integral to ATM switching nodes and will have robust interoperability with other Sonet networking elements.

An access layer of service-rich ATM will be distributed into residential and large campus/building environments. The rapid emergence of broadband cellular technologies that provide "follow-me" broadband connections to customers' mobile computer systems and personal agents will add some complexity.

In this phase, narrowband voice switches will rapidly become telephony servers on the ATM fabric. Interworking protocols and virtual routing services have matured to support connections between customers with narrowband access and customers with integrated multimedia connections. Narrowband-to-broadband service internetworking will become a reality, providing a seamless service migration for end users.

Carriers will maximize their ATM investment by making the appropriate transition from one deployment phase to the next. Recognizing when new opportunities arise and capitalizing on those opportunities will determine which carriers experience the highest profit levels and obtain the best return on their investment.

Philip Yim is Manager of Broadband Product Line Management for Siemens Stromberg-Carlson, Boca Raton, Fla. Ehab Shafik is Director of Product Marketing for Newbridge Networks Inc., Herndon, Va.