Welcome mat to the WAN Offering customers the right access options will be key to broadband service success

Wide area network speed requirements are on the rise. A growing number of Internet protocol-based applications that support voice and video are moving into the WAN. Image-intensive tasks-such as transmitting large files from advertising agencies to pre-press shops-need more speed. With the advent of low-cost codec and video compression devices, customers are demanding multimegabit connections between locations for high-quality video networks in the broadcast, education, finance, insurance and medical industries.

Unfortunately for customers, islands of 10 to 100 Mb/s local area network connectivity run up against the T-1 bottleneck in the WAN. Even with routers that use load sharing to map packets across multiple T-1 lines, each application is limited to 1.5 Mb/s. Yet today's WAN customers can't justify the cost of T-3 unless they are buying seven or eight full T-1 lines. A recent tariff survey reported that the monthly cost of a 400-mile T-1 line from an interexchange carrier was $6200, compared with $39,000 for a T-3 line.

Inverse multiplexing, which combines multiple T-1 lines into a single clear data channel of 3 to 12 Mb/s, is one alternative. The inverse multiplexing for asynchronous transfer mode specification-a cell-based protocol for ATM access over multiple T-1 lines-should be finalized by the ATM Forum in mid-1997.

In the meantime, service providers are beginning to adopt bit-based inverse multiplexers as part of an integrated access platform that can be put in service today.

Bit-based inverse multiplexers can create a pipeline with the bandwidth of multiple T-1 lines that is independent of the application running on top of it. A carrier can run multiple services-including ATM, frame relay, ISDN, time division multiplexing (TDM) and switched multimegabit data service (SMDS)-on this logical pipe. Deployed close to the customer premises, this access platform can serve as a welcome mat to a carrier's broadband network, offering customers the bandwidth and service flexibility they desire.

Rolling out the mat Hybrid private/public networks are evolving against a backdrop of increased competition in data transmission services. Local exchange carriers are upgrading their infrastructures to provide more advanced high-speed data switching and transport services. With the prospect of deregulation that will erase LATA restrictions, LECs are positioning themselves as operators of geographically-dispersed, full-service networks. Their new networks will be capable of transporting and interconnecting all types of traffic-from leased lines to public network services such as ATM, frame relay, ISDN and SMDS.

Carriers have invested in multiservice switching platforms that can support switched virtual circuits and the translation between different frame and cell formats. But the high cost of these nodes limits their use to deep in the network. Carriers struggle with providing access on a wide scale, especially when some customers may be located hundreds of miles from the nearest switch.

Instead of backhauling traffic miles to the nearest switch, carriers are investing in a new generation of "edge vehicles" or integrated access platforms that are being deployed close to the customer premises.

These access platforms help carriers extend new services and higher levels of bandwidth to the customer at a lower cost per bit. Integrated access platforms provide connectivity to all the customer's applications and efficient use of the access facilities, whether they are T-1, inverse multiplexer circuits or T-3 links (Figure 1).

The hallmarks of tomorrow's broadband integrated access platforms are modularity and centralized control over all resources.

The access platform has swappable interfaces to allow the customer's voice, data and video applications to evolve. Making changes in carrier services such as ATM, frame relay, ISDN and SMDS is as easy as programming a data terminal equipment port or sliding in a new service access module. Support for multiple services allows WAN managers to migrate their networks as the services evolve to take advantage of new features.

For example, a user might start out with ISDN and frame relay service. When new ATM services became available, the user could add an ATM access card to the platform and begin a pilot network. Once the network was proved, ISDN service could be phased out and the frame relay circuits could be tied into the ATM network.

Customer benefits By adding inverse multiplexing as a network interface, carriers can implement fractional T-3 services to generate new revenue while offering their customers a cost structure they can justify. Users reap cost savings by combining communications applications. They also gain flexibility in the choice of services and bandwidth selection as they move beyond T-1. With high-speed frame relay or ATM service, for example, a single data pipe from an inverse multiplexer can be divided into several logical channels to serve different routers.

High-end ATM switches aren't needed at most remote sites today. An access concentrator configured with multiple T-1 lines and inverse multiplexing capabilities can deliver all the necessary services most sites need-and do it more cost-effectively than a DS-3 line. Inverse multiplexers represent the "right sizing" of bandwidth for remote access in today's market.

Even though fiber will play a greater role in the local loop, carriers must continue to meet the needs of their installed base with improved access to enhanced services that use the existing copper wiring plants. WAN customers are interested in trying out new services and moving up the bandwidth ladder starting with multiple T-1 based services.

That's not to say that future high-volume sites won't need DS-3 and OC-3 interfaces based on ATM. With the increased bandwidth demand of the Internet and multimedia applications, the need for fiber will begin in the network and then emanate to the edges. The challenge for carriers is to deploy network access architectures that provide faster access today and that will also provide a transition to broadband.

Modular access platforms offer a smooth equipment migration path and more granular control over bandwidth than the one-box, one-service access solutions of the past. The logical way to migrate from T-1 to higher speeds is to first incorporate inverse multiplexing. With the common platform approach, the customer is not making T-1 equipment obsolete or putting in a new stand-alone inverse multiplexer network. Bandwidth can be added to an inverse multiplexer channel in T-1 increments. At some point, the customer may move up to a DS-3 circuit by adding an access module, not another stand-alone box.

Carrier benefits Broadband integrated access platforms use DS-0/DS-1 and DS-1/DS-3 cross-connect capabilities to map application traffic. Having multiplexing, grooming, channelization and concentration capabilities close to the customer premises can help make transmission within the service provider's network more efficient. Multiple inverse multiplexer channels can feed into a DS-3 circuit for consolidation in the central office. Circuits can also be groomed so that fully-filled pipelines feed the carrier's backbone to maximize the use of switch ports.

From the carrier's perspective, consolidating access at the physical level simplifies the network and reduces costs. Cost savings accrue because bringing multiple services into the backbone requires less circuit provisioning. Running multiple services over multiple networks requires installing and maintaining separate network interfaces and management infrastructures for leased lines, ISDN, frame relay and ATM networks.

By standardizing on an integrated access infrastructure, carriers can reduce the amount of engineering required for installations and changes, as well as the amount of ongoing operations management support required. Integrated access platforms reduce the number of network interfaces and access boxes that are needed on the carrier side as well as the customer side (Figure 2), which reduces hardware costs and uses less floor space. With fewer components to manage, the network is more reliable and fewer resources are needed for network management.

Rather than requiring separate management systems for each type of service, the integrated access platform brings protocol processing, transmission, signaling and switching under a common umbrella with a single management station. As users' service requirements change, new network elements are added, yet they remain under the control of the platform's unified network management system. Minimizing the actual physical changing of the hardware and moving toward software-defined networks simplifies provisioning.

Broadband integrated access platforms are designed to give customers easier access to multiple services. By effectively incorporating network management, these platforms can break down the wall that has existed between the customer premises communications equipment and the services delivered to them.

Not only will service providers be able to see out to the customer, but the customer will be able to see out to the services they use. By opening up the access platform's network management capabilities to the customer, service providers can design networks in which customers have control over their destiny, much like what they have with private networks.

Customers may wish to participate in refining service requirements such as the size and burst capacity of their permanent virtual circuits. Bandwidth-on-demand capabilities can be provided by allowing the customer to dial up additional bandwidth as needed with switched digital services.

In addition, carrier responsibilities such as fault detection, isolation, correction and automatic rerouting can be extended from the carrier backbone out to the customer premises and closer to the end user.

The ubiquitous wide area ATM backbone is probably years off, but many corporations are planning an integrated services architecture based on broadband ATM switches in their internal networks. These internal switches can be used to provide all of the transport services that dedicated LAN hubs, routers, key systems, PBXs and video codecs use today.

In these applications, providing remote access for multiple services across the WAN will continue to be the job of the ATM access concentrator within the broadband integrated access platform.

Kevin R. White is Director of Marketing, and Richard A. Sweatt is Director of Business Development for Verilink Corp., San Jose.