Integrating sonet- and Ethernet-based service provision

As the local market heats up, competitors will have to adapt their voice-based networks to carry a variety of traffic, particularly IP signals.

Andrew Knott Positron Fiber Systems

Many competitive access providers and competitive local exchange carriers provide business services over Synchronous Optical Network (sonet)-based fiber-optic rings. The use of sonet rings gives them significant advantages over the predominately copper-based access networks of their incumbent competitors. To date, these competitive carriers have grown by using their rings to provide high-quality, low-cost solutions for voice. However, according to industry experts, 50% of all backbone network traffic will be Internet-based by year-end 2000, making this one of the highest growth opportunities for competitive access providers and competitive local exchange carriers. Supporting this growth presents voice-oriented carriers with significant challenges. These carriers are required either to implement entirely separate local area network (lan) and voice/data fiber access networks, which increases fiber requirements and network deployment cost, or to provision Ethernet services over their sonet access networks.

In order to provide Internet connectivity over traditional sonet access networks, carriers typically employ external devices, such as bridges, Ethernet switches, or routers, to support lan-based traffic (see Fig 1). While this approach allows carriers to deliver lan services, it is not cost-effective in terms of capital cost and complexity at the network access point. Using two entirely separate technologies for the delivery of voice and Internet services means that carriers have to face the problems associated with multiple management systems and the different provisioning methods for sonet ring and lan access equipment. In addition, typical lan access solutions are focused around "in-band" simple network management protocol-based management rather than on the "out-of-band" Open Systems Interconnection-based management architectures found in sonet-based access equipment. Finally, the skills necessary to provide field engineering support of sonet T1/T3 equipment are very different from those required to support router-based solutions. The result is that many competitive carriers are forced to run two separate support organizations--one to support voice delivery and the other to support Internet access.

The alternative for competitive carriers is the integrated sonet broadband access multiplexer with an Ethernet mapper card, which provides carriers with the ability to provide direct lan connectivity integrated inside their business service-delivery vehicle. This enables carriers to provision 10- and 100-Mbit/sec Ethernet connections from customer locations to their Internet backbone, using techniques and management tools that are identical to those used for voice circuits. This also gives them a single platform for the delivery of business services, which meets the requirements for network reliability that business customers demand (see Fig. 2).

Integrated Ethernet mapper cards provide carriers with an ideal vehicle to transport 10- and 100-Mbit/sec Ethernet services over a sonet access network by integrating the Ethernet line interface directly into the sonet add/drop multiplexer located within the customer premises and the carrier`s central offices (COs). It connects to intelligent lan equipment (customer-supplied bridges, routers, and firewalls, for example) rather than directly to customer lan networks. It provides "native-mode" lan connections between two Ethernet lans via a sonet network. Thus, it is an ideal solution for both high-bandwidth Internet service delivery and for transparent lan service (tls) delivery (see Fig. 3) over the same platform and on the same fiber routes as conventional T1 and T3 voice and data service delivery.

Benefits

One of the key benefits of the integrated broadband access multiplexer is a reduction in the cost and complexity of the equipment needed to deliver services at the customer premises. A typical comparison of the customer-located equipment required to deliver four T1 circuits for voice service and a high-capacity (4 ¥ T1) Internet circuit over a sonet access network is shown in the table.

Because sonet-based Ethernet mapping uses the sonet multiplexing hierarchy, it can be directly integrated into CO digital crossconnect-based architectures. This allows lan traffic to be separated from voice traffic at the CO, with voice traffic routed to local switching and interexchange carrier access portions of the network and Internet traffic to be connected directly to the Internet service provider CO routing platform. In this way one of the primary benefits of sonet-based networks is realized--the combination of multiple services with a minimum of multiplexing stages, which leads to carrier service cost reduction.

In conclusion, the use of integrated broadband access multiplexers enables carriers to deploy high-bandwidth Internet services as easily and reliably as the voice services on which they have built their revenue. At the same time, these multiplexers minimize the impact of integrating enterprise-focused access platforms into their networks. u

Andrew Knott is vice president of sales and marketing at Positron Fiber Systems, Mt. Laurel, NJ.