The new local loop: Future generation DLCs have all that yesterday's solutions had-plus a way to manage the new local loop

Carriers hoping to succeed in the new local loop are realizing that the next generation digital loop carriers they have deployed over the past 10 years can't meet today's competitive marketplace demands. Fortunately, local exchange carriers and competitive LECs have an alternative-future generation DLCs.

Future generation describes a DLC technology that combines all the features of yesterday's next generation solutions, including voice and data service interfaces from POTS up to T-1, with an evolutionary path to address the needs of the new local loop. Specifically, future generation DLCs can accommodate a mixture of narrowband and broadband services, as well as circuit and packet services such as asynchronous transfer mode and Internet protocol (IP) on one common platform.

Whereas next generation DLCs require carriers to buy additional elements such as digital subscriber line access multiplexers to enable their networks to carry broadband services, future generation DLCs use the existing network infrastructure without creating a need to invest in new, expensive equipment.

Many industry experts agree that the regulatory climate and the entry of new service providers to the local loop have escalated the urgency for carriers to upgrade or rebuild their infrastructures to satisfy demand for emerging broadband services and ultimately to remain competitive. In the long run, carriers might deploy broadband hybrid fiber/coax, fiber to the curb or home or wireless local loop technologies.

Experts also agree that these alternatives require huge capital investments and won't be widespread for the foreseeable future. As a result, LECs that develop a viable local loop broadband services strategy will secure a valuable competitive advantage in a market that is expected to grow beyond $1.5 billion in 1998.

Many large service providers have reissued local loop requests for proposals because the integration of broadband services has not been addressed sufficiently, the Ryan, Hankin, Kent consultancy has found. A product such as future generation DLC would be cost-effective and efficient, the consultancy reports.

Future generation DLCs meet the essential technology requirements for long-term success by providing an economical and efficient way to add more narrowband services. In addition, they provide an efficient reuse of the existing copper plant, an easy integration path to fiber, a quick return on investment and a platform that can support future broadband services.

Four key areas in which future generation DLCs meet these requirements and differentiate themselves from their predecessors are an advanced feature set, integrated transmission interfaces, support for all network topologies and state-of-the-art element management.

A unique feature set To enable carriers to provide an efficient and economical long-term local loop solution, future generation DLCs must feature automatic system configuration and operation, automatic subscriber line testing and reporting, software download, intra-calls to increase traffic capacity, and multiplexing and concentrating operating modes.

Rounding out this set of features are three critical attributes that affect the bottom line-facility relief, modularity and compactness. A future generation DLC's most important function is to use existing wires or fiber optic cables in the local loop to promptly satisfy the increased demand for telephone and advanced services. The newest DLCs accomplish this by expanding the channel capacity of existing loop plants, enabling telcos to add more subscribers to the network and provide sophisticated digital services without significant investment in cable infrastructure. The Yankee Group has found that the future generation DLC has merit because it conserves bandwidth requirements between the DLC and the central office.

Modular growth gives telcos the benefit of minimizing initial capital investments while optimizing the use of existing infrastructure. Because future generation DLCs expand modularly, they satisfy customer needs as demand for service increases. In areas where significant demand is anticipated, the DLCs eliminate the costly and time-consuming task of laying new cables, thus providing services quickly and economically. At any time, a system's capabilities and capacity can be expanded with minimal incremental cost by adding new line cards or by linking another shelf.

The smaller size of future generation DLCs, the result of the hardware's compact and dense design, provides financial benefits to the carrier. The size of a future generation DLC is comparable to the size of a microwave. The considerably smaller future generation DLC is even more powerful, carrying 16 POTS lines on a single card, compared with next generation alternatives that have four or six POTS lines per card.

The reduction in size translates directly into reduced square footage, inventory space and shipping costs; lower total cost to the customer; lower manufacturing and production testing costs per line; and lower cabinet costs.

Integrated transmission interfaces Integrated transmission interfaces are essential to the definition of future generation DLCs because they eliminate the need for external transmission equipment, which saves space, power, cabling and subsequently, costs.

While interfaces such as high bit-rate DSL (HDSL) and standard T-1 are important elements in future generation DLCs, an optical interface lets fiber technologies extend to the local loop, providing an evolutionary path to more advanced broadband services. The use of fiber optics enables transportation of extra bandwidth-such as non-switched 1.544 Mb/s signals-simultaneously with more traditional narrowband traffic.

In addition, fiber optics as a transmission media with future generation DLCs is simple because external optical multiplexers and their associated equipment, such as power supply, housing, control and management, are not required. With the new DLCs, upgrading from pulse code modulation (PCM) over copper to fiber can be performed easily by replacing the appropriate T-1 interface card with the integrated fiber optic interface.

Network topologies For a DLC to be classified future generation, it also must be suitable for any network topology, including point-to-point, star, ring and mixed. Cost savings can be demonstrated in the case of the add/drop and ring topologies. These configurations consist of numerous cascaded DLC remote units that use the same media connected through digital links to a single central unit. Because a future generation DLC directs all services from various remote units to a single central unit, a small space is required at the CO, leading to substantial savings in space and cost.

Figure 1 shows how a future generation DLC can be applied with a DS-1 level connection to the local exchange using a star topology over multiple transmission bearers such as fiber, T-1, HDSL and PCM. The topology's advantages include single point management for the entire system, minimal exchange building space required and maximum use of existing network infrastructure.

The final element in the future generation DLC package is an advanced network management system that allows local or remote access to all administrative functions (Figure 2).

For ease of use and efficient management, the system should be a PC-based Windows application that includes dynamic system status and configuration reports, complete subscriber line testing capabilities, subscriber administration, alarm and error reports, traffic statistics, performance monitoring and event history.

Today's telecommunications market and the local loop in particular are developing and changing rapidly. The result is an urgent need for new, cost-effective solutions to satisfy customer demand. Although next generation DLCs were sufficient in the recent past, carriers have a new set of challenges that the newly coined future generation DLCs are poised to meet with a unique package of advanced design and powerful features.