Fiber rings avoid disruption

Fiber rings avoid disruption

paul palumbo

Atlanta-based Cox Cable Communications Inc. is attempting to gain local access market share at the expense of telephone company competitors by deploying a ring- in-ring fiber-optic network architecture. According to Cox, the architecture is engineered to minimize downtime and maximize application-specific flexibility.

The strategy of Cox`s ring-in-ring architecture is to provide such services as plain old telephone service and new-media digital applications. The basic structure of the ring-in-ring arch itecture comprises dedicated node rings in which fibers originate at the headend and run to each node in opposite directions. Broadcast backup and digital loop-through rings follow the dedicated ring routes. Fibers in the loop-through rings pass through each node and terminate at the headend.

The ring-in-ring architecture strives to prevent any disruption of service. To that end, two types or bundles of fibers--dedicated and loop-through--provide dual levels of redundancy by connecting the headend to the network nodes in two separate ring configurations.

At one redundancy level, the dedicated rings permit signals unable to reach a node because of a network failure to reverse direction and ultimately arrive at the destination node by circling in the opposite direction.

Via the second level of redundancy, should the entire dedicated node ring fail, the transmissions are all switched over to the broadcast loop-through ring.

The dedicated fiber bundle passes all the nodes but delivers traditional cable-TV services to only one designated node. It also carries the reverse signals from the node back to the headend.

On the other ring, the two loop-through fiber bundles carry telephony and video services to all the nodes and relevant information back to the headend. The broadcast bundle serves as a backup route for the dedicated fiber bundle.

The dedicated and loop-through rings consist of four fibers each. Two fibers facilitate the deployment of the digital loop carrier, synchronous optical network add/drop multiplexers and other hardware needed to multiplex subscriber communications paths onto a single, high-speed signal. The second pair of fibers serves as redundancy support.

Alex Best, Cox` vice president for engineering, says the cost of a ring-in-ring overbuild with four fibers in each bundle is comparable to traditional 8-fiber bundles per 1000-home hybrid fiber/coaxial-cable networks.

The ring-in-ring architecture is estimated by Cox to be 5.4% cheaper to install than a typical 8-fiber "star-bus" design. The chief requisite, however, is that network rebuilds take place in urban, or "clustered" regions.

Best estimates install costs shake out at close to $15,000 per mile when upgrading a node from 300 megahert¥to 750 MHz. The fiber components are estimated at $3000/mile, and the coaxial-cable portion--including taps, amplifiers and components--runs approximately $12,000/ mile.

Sections of the ring-in-ring network are scheduled to be installed by the end of 1996 in Omaha, New Orleans, San Diego, Hampton Roads, VA, and Oklahoma City. The five sites hold approximately 29% of Cox`s 3.1 million cable subscribers.

Like other multiple system operators, Cox is investing heavily in new fiber plant. But Cox has decided to further stretch its rebuild dollars by installing multiple fiber layers; this should result in lower average service hours per year that customers experience service disruptions.

For several years, the reduction of downtime has been a consistent trend in the telecommunications industry. System and component design improvements made since 1989 have lowered average downtime hours in a typical star-bus network by 3.5 times, to 1.5 hours in 1993. Cox` cable-TV technical requirements specify a median figure of 2.5 hours per year.

Bell Communications Research`s standard for telephone services, by contrast, establishes an average customer outage time of less than 53 minutes per year, which translates into availability of just less than 99.99% annually. According to Cox engineering documents, its ring-in-ring architecture will meet--and exceed--anticipated broadband operating requirements.

Cox is expanding Bellcore`s mandate to include standards of reliability for interactive targeted classes of delivery such as video on demand, near video on demand and advertising.

The bottom line is that Cox is counting on its ring-in-ring fiber plant design to offer higher levels of reliability than presently available--albeit transparently--while providing the backbone of a new broadband pipe into the home.

Fiber rich

As Cox transitions from a one-way delivery provider to a full-service network administrator, incremental sources of revenue from valued-added services via high-speed data delivery are expected to shorten payback windows.

A key network theory Cox is trying to prove, according to George Gautereaux, vice president for technology, is that the installation of fiber-rich networks will go a long way toward expanding the company`s franchise all the way to the desktop computer.

Gautereaux says hooking up personal computers to coaxial-cable drop lines is a minor step that could pay major dividends in incremental online service revenue. That is why Cox has been testing cable-modem technology with Prodigy online services over its hybrid fiber/coaxial-cable plant in San Diego.

Gautereaux claims 40% of Cox subscribers in San Diego own computers, and there is a correlation between users of one pay-as-you go service, namely cable TV, and emerging technology. Admittedly, he notes some of the computers are older 286-type machines, or boxes without modems.

Currently, 150 subscribers are gaining access to Prodigy via Cox`s cable plant at speeds approaching 500 kilobits per second, or 35 times faster than that of a conventional 14.4-kbit/sec modem. That is why Cox aims to challenge entrenched telephone company dominance of the online delivery universe. Gautereaux also maintains Cox will "focus on providing high-speed Internet access."

According to industry analysts, the main difference in competitive subscriber services is choice. What the telephone companies have learned from beta technology testing (and limited broadband deployment) is consumers will migrate to providers that offer new levels of enhanced services, including the "convenience" factor. q

Paul Palumbo is a freelance writer based in Seaside, CA.

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