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Migrating new services over Sonet

Mon, 05/31/1999 - 8:00pm
Bill Zornow, Director of Network Operations, Buckeye Telesystems

As a facilities-based, cable-affiliated regional competitive local exchange carrier (CLEC), Buckeye Telesystems is making strides to generate a base of new business customers for a mix of dialtone voice, data, video and ISP services. Concurrent projects underway at Buckeye Cablesystems, the affiliated cable TV provider, include the ongoing upgrade to hybrid fiber/coaxial infrastructure and a rollout of high-speed cable modem services.

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Figure 1: Network Operations Center to hub to node.

These businesses each offer the opportunity to develop superior infrastructure for large, under-served business and consumer segments. Buckeye Telesystems had decided several years ago to base its northwestern Ohio area services strategy on Sonet, to deliver fiber optic reliability and traffic management capacity. The decision has provided an excellent opportunity to develop a shared architecture for high reliability, high-availability services that can be collectively managed across both the CLEC and broadband HFC infrastructures. The choice of Sonet has tradeoffs. In particular, there was the problem of how to most efficiently use fiber capacity, central office and hub site real estate and network engineering investments. This threatened to create escalating costs for supporting unpredictable growth in a set of services that range from cable modems to private line and frame relay services.

In order to plan for more effective growth, Buckeye Telesystems decided to deploy the Cerent 454, a new multiple-service, optical transport system designed to support mixed data, video and voice services. Based on preliminary field testing, Buckeye is now deploying Cerent's transport technology in a single OC-48 ring, with plans to expand to five rings and 15 terminal nodes. This article features a discussion of this decision, first in the HFC context and then in the CLEC environment.

Buckeye Cablesystems is currently in the second year of a $120 million infrastructure upgrade encompassing both cable and telephony operations. On the cable side, services will be delivered over a single-cable, 860 MHz network, utilizing hybrid fiber/coax architecture to residential customers. It will support a wide variety of broadcast and interactive services, including cable modems-both two-way and telco return services-that will be offered by Buckeye's affiliate ISP, Access Toledo. Concerns about maximizing the HFC infrastructure led Buckeye to choose Sonet as the primary vehicle for carrying data traffic to hub sites located throughout the metropolitan Toledo area in support of cable modem deployment.

The upgraded HFC infrastructure consists of 12 hubs in a multiple ring configuration to the headend via four fiber optic rings, with up to 40 nodes in a star configuration per hub, serving an average of 500 homes per node via an 860 MHz single coaxial cable. Of the more than 200,000 homes that Buckeye Cablesystems passes, there are currently more than 130,000 subscribers for cable service. Given this relatively high take rate, Buckeye faced a welcome, but serious, potential for early acute IP traffic management problems created from growing levels of cable modem usage.

The challenge was to find a solution that would allow for the efficient and robust transportation of the upstream traffic from the hubs to the central office for processing, while providing a platform to other current and future telecommunications services.

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Figure 2: The network offers a migration path to support multi-service flexibility.

With hubs serving from 20,000 to 60,000 homes passed, the dimensions of the problem are clear: the deployment of cable modems represents an undetermined level of data traffic for planning purposes. The Buckeye Express cable modem service offers speeds of 512 kbps downstream and 128 kbps upstream. As the number of high-speed cable modem service subscribers to each hub increases, aggregated bandwidth requirements can easily outstrip the infrastructure, and thus reduce the level of service experienced by customers. A solution was needed to allow for economical transport of IP-based traffic and the graceful growth of services. The Cerent optical transport system was chosen to fill this need. By offering a native Ethernet interface within the Sonet infrastructure, the system allows for an efficient combination of a variety of service transport needs on a single platform. In addition to providing bandwidth for potentially growing cable modem services, this HFC architecture, supported by a Sonet infrastructure, allows Buckeye to maximize the utilization of its investment in fiber engineering and existing fibers already in the ground.

In addition to the utilization of the overall network investment, this solution allows Buckeye to offer data services with high availability, over the HFC plant and through direct connection to the customer. A similar approach will be used in offering lifeline services, such as telephony, over coax cable without incurring additional upfront costs.

In summary, the need to support new services and new architectures has given cable operations a challenge to redefine the methods for information transport. The use of a next-generation Sonet product gives Buckeye a distinct advantage in the successful deployment of data transport services based on cable modems. This also allows Buckeye to offer a broad range of services, and to do so in a manner that will allow for significant growth.

As a CLEC, Buckeye Telesystems has a well-defined rationale for the management of its data infrastructure over Sonet. Certified by the Public Utilities Commission of Ohio, with customers in northwest Ohio (and with an application for service in Michigan), Buckeye is one of only a few facilities-based CLECs in a territory that crosses three large local exchange carriers-Ameritech, GTE and Sprint. In 1998, Buckeye made a commitment to expand its service offerings by adding a Lucent 5ESS 2000 switch and a Newbridge ATM/Frame Relay switch. These are maintained at a central operations facility connected to an OC-12 Sonet fiber optic ring, with 15 previously built subtending rings. To this, Buckeye is adding Cerent's 454 product, to build out an OC-48 ring and to simultaneously support additional services, both electrical and optical.

Buckeye Telesystems offers services to small- and medium-sized businesses from a menu of dial tone, private line and frame relay services. Although this has been a great opportunity, the demand for large-pipe data connections has made it difficult to analyze patterns and plan for efficient usage of Sonet infrastructure.

Because the amount of traffic is growing, traditional Sonet presents two challenges that threatened to curb Buckeye's ability to support customers' bandwidth requirements. First, using existing Sonet gear, it is impossible to increase bandwidth on a ring segment without upgrading all of the Sonet gear on the ring. This can make it cost-prohibitive to offer high-speed services on a point-to-point basis for large customers. Secondly, limited co-location real estate is often consumed by larger, traditional Sonet gear, limiting the ability to install the necessary cross-connects and ATM switches to support lower speed electrical and optical services. Many customers buy fractional DS-1 Frame Relay service.

The addition of a next-generation add-drop multiplexer (ADM) resolves both of these problems. Increasing the speed of an existing ring involves changing line cards, rather than replacing an optical switching core and chassis. Additionally, it functions as a cross-connect and an ATM switch, providing both electrical and optical services from a single chassis, thus eliminating the need for additional boxes to provide low-speed electrical services. As a relatively new CLEC, the device helps Buckeye overcome a number of difficulties. Most significantly, it has allowed the company to extend its price advantage to data service customers without incurring the need to upgrade capacity on the Sonet rings. An OC-48 ring can be installed for the same cost as traditional OC-3 Sonet. Today, Buckeye can offer point-to-point OC-3 services across multiple RBOC territories for a lower price than competing DS-3 services.

The most expensive component of maintaining Sonet is the labor in constructing the new fiber capacity. Buckeye can now engineer at 96 fibers in the backbone, and upgrade to OC-192 simply by the addition of new line cards. This is without additional investments in fiber engineering, splicing and upgrades. In this approach, Buckeye is using the Cerent gear to build multiple OC-48 rings and to reduce expenditures for cross-connects and ATM switches. Most striking, though, among the capabilities that now exist is the ability to offer "any optical level in, any electrical level out." This enables Buckeye to offer a variety of popular data-service connections to customers, including OC-n, T-1, T-3, DS-n Frame Relay and ATM.

Buckeye Telesystems chose Sonet in the first place for its reliability; this new equipment makes it multi-service. Buckeye now also has the ability to add line cards to these nodes for multiple services in order to support new services at these locations. Because Buckeye Teleservices' infrastructure can potentially support other groups, creating multi-service flexibility supports the strategies for product development as a CLEC, a cable company and an ISP.

E-mail: bzornow@buckeye-telesystem.com

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