Continental upgrades hybrid networks
Continental Cablevision of Los Angeles, the nation`s third-largest cable-TV operator, with 3.2 million subscribers in 16 states, has found that a single hybrid fiber/coaxial-cable architecture does not fit all its system requirements as the company moves forward with network upgrade plans to provide telephony, high-speed data and video-on-demand services in California.
The magnitude of this $700 million fiber network and cable project is also illustrated by company plans to upgrade 14,300 miles of fiber-optic and coaxial cable with call-switching systems and new home wiring (see Lightwave, October 1995, page 3).
The core of the backbone fiber ring may be a synchronous optical network which can be used for the company`s planned telephony services. According to David Fellows, Continental`s senior vice president of engineering, "One architecture is used throughout the company`s systems, but a modified one is being deployed both in California and at Boston College, where the company recently completed a network build."
Continental`s basic architecture is hybrid fiber/coaxial cable, or fiber-to-the-serving area, taking active fiber strands to more than 1000 to 2000 home pockets. According to Fellows, there is enough fiber in the cable to split that node into 500 home pockets with approximately four fibers serving the area. He says that architecture-system planning in Continental`s five service regions is relatively easy at the parent company level because he first defines business guidelines. Then, the company`s regional operators are responsible for creating the design, reviewing it with Fellows and sending out the purchase orders. He also notes that "all the hard work is done at the regional level." He says the company uses C-Cor Electronics Inc.`s fiber-optic cable (C-Cor is the company`s principal supplier). Pirelli Cable Corp. and Antec Corp. supply its fiber requirements.
Peter Krasilovsky, senior analyst at Arlen Communications, says, "Continental Cablevision has always seemed to know what is required to compete effectively as next-generation services roll out." He notes that "at the same time, Continental has been cautious about embracing technologies that would later have to be torn up."
Knowing what technology makes sense to compete effectively in California has convinced Continental to install a modified ring-ring-bus architecture pioneered by Cox Cable Communications. The basic topology is a primary ring in which fibers originate at the headend and run to each node over several routes. A second ring is deployed as a continuous loop-through configuration that rides piggy-back on the first ring. That second fiber ring takes the build out to a 2000-home pocket. Off-the-node is a "one-hop" star fiber configuration serving a 500-home cluster.
Continental chose the modified hybrid fiber/coaxial-cable network for California because of the way "Los Angeles is laid out, as opposed to New England, where there is usually only one way to get from here to there," according to Fellows. Another reason the ring-ring-bus architecture was selected had to do with high-redundant qualities, which exceed 99.99% reliability and meet the Bell Communications Research Corp. Technical Requirement-909 lifeline reliability standard specification.
Although Continental does not have a telephony partner (the company dropped out of its Sprint alliance because it viewed wireless as an interim network solution), it hopes to sell telephony, high-speed data and video-on-demand services to its 930,000 subscribers in California. Continental is spending $700 million in the state and plans to wire homes in Fresno, Kings, Los Angeles, Madera, Orange, Riverside, San Joaquin, Sutter, Tulare and Yuba counties.
Boston College network
As for the Boston College network build, Fellows says that "what the company is doing there is applicable to general system rollouts, and it`s basically a 10,000-connection home pilot system."
Although Boston College was the first academic campus network that the company built, there are unique aspects to the network. First, Continental thinks that it was significant that a cable company was invited into a university setting to manage the data network design. And second, the company has extended that network off campus and into professors` homes in almost 10 towns in the surrounding area. The professors` homes have 10-megabit-per-second connectivity access to the university network.
The Boston College network design involves a dedicated fiber-optic ring architecture from Continental`s Network Control Center in Needham, MA, out to the college`s on-campus hub site. From there, approximately 18 independent fiber nodes, each feeding separate coaxial-cable systems serving drop locations, are deployed across the campus,
The 750-megahert¥network can deliver video, data and telephony services, including:
Data transport over an asynchronous transfer mode, or ATM, backbone
Ethernet access to residence halls, including more than 10,000 service outlets via the cable network
Ethernet speed connections to be expanded to full ATM (155 Mbits/sec)
An 80-channel analog system that can be upgraded to a 720-channel digital interactive system
Five channels of in-house programming specific to Boston College.
According to Fellows, there are important challenges to deploying hybrid fiber/coaxial-cable networks--how the network is powered and eliminating ingress or back-channel noise. Another issue involves how to power the network when local 110-volt power from the electric utility goes out.
He adds that Continental is looking at batteries for standby power, which the cable-TV industry has only used to a limited extent to back up its systems.
Fellows says, however, that the company is looking for a better way to do it, which may involve a joint venture with a local utility. Continental is attacking the ingress problem by installing blocking filters, so that any noise that originates in homes "cannot go up the drop and contaminate the core system." Cable companies already have to meet a requirement known as cumulative leakage index, which specifies that signals from cable-TV plant cannot leak out into the atmosphere because of potential contamination of radio navigation traffic to route airplanes.
Commenting on the hybrid fiber/coaxial-cable network versus switched-digital-video fiber-to-the-curb debate, Fellows says the hybrid systems are not as neat and clean in the real world as they appear on view graphs.
The threat for the regional Bell operating companies, he adds, is that they could go into another "analysis paralysis" if switched-digital video`s move from trial to deployment does not meet operator expectations. He says that regional Bells going with switched-digital video are likely to find out that "ingress and powering issues are even more problematic with fiber-to-the-curb architectures." He adds that the cost/benefit rationale of taking fiber to the curb is not that attractive, considering that most people just want more channeling options, not necessarily two-way interactivity. q
Paul Palumbo writes from Seaside, CA.