Time Warner upgrades HFC networks with modems

Time Warner upgrades HFC networks with modems

PAUL PALUMBO

Time Warner Cable (TWC), in Stamford, CT, has begun activating parts of its national hybrid fiber/coaxial-cable (HFC) network after almost three years of deploying fiber-optic cable. While not the largest franchise, TWC`s Akron/Canton, OH, 750-MH¥HFC network is expected to have its first cable-modem service activated by year-end 1996. Other HFC cable-modem system turn-ups are planned for San Diego, CA, and Binghamton, Elmira and Corning, NY.

The company has not hesitated to put up resources to upgrade its clustered systems with HFC networks, particularly in New York City, with 1.1 million subscribers; Tampa Bay, FL, 683,000 subscribers; Central Florida, 583,000 subscribers; Los Angeles, 327,000 subscribers; and Rochester, NY, 294,000 subscribers.

Mario P. Vecchi, chief network engineer for the Excalibur Group, a Time Warner company, describes its network cable-modem capability as "allocating resources in a particular region to get a system upgraded." The company`s cable-modem access system is called Road Runner, a service brand of the Excalibur Group.

As for all of TWC`s networks, Vecchi predicts that nearly 50% of the company`s systems are upgraded, and the remaining networks are expected to be complete by year-end 1998. A recent study by Merrill Lynch concluded that TWC is expected to finish its HFC network upgrade build by 2000 at a cost of $3.5 to $4 billion, or about $180 per passed home.

As the nation`s second-largest cable-TV multiple system operator, TWC has 11.7 million subscribers, with a total of 17.3 million homes passed. Mike Luftman, TWC spokesperson, says that most of the company`s fiber is purchased from Corning Inc. in Corning, NY, and Siecor Electronics Inc. in Hickory, NC.

TWC`s fiber network has made the company one of the country`s largest buyers of fiber-optic cable over the past several years. With such an investment, TWC can leverage its 750-MH¥systems into a variety of marketing positions, including local telephone services, cable-modem delivery and interactive digital television.

Network upgrades

TWC`s HFC network is typically fiber-to-the-node, with each node serving 500 homes. Going back upstream, a headend arrangement drops down to distribution hubs on the order of about 20,000 homes per hub. Fiber optics provide backbone network connectivity to the headend, where the server complex is located. In Akron and Canton, both communities constitute a single deployment; TWC is using Fiber Distributed Data Interface (fddi) transport technology to connect all the distribution hubs back to the headend.

A cable modem terminates the signal conversion system at each of the network`s 10 distribution hubs. Fiber connectivity back to the main server complex is similarly made using fddi. TWC typically uses singlemode fiber at a 1350-nm wavelength. Fiber strands, depending on the length of cable, can run from 24 to 36 strands per cable. The Road Runner cable-modem service requires two fiber strands per fddi link.

Both transmitter and receiver electronics were purchased from General Instrument. For upstream data traffic, Fabry-Perot semiconductor lasers are used. Since a much broader array of information has to be transmitted downstream, the company uses more-expensive distributed feedback lasers, operating at 1350-nm wavelengths.

The Motorola cable modems are capable of delivering data downstream at about 27 Mbits/sec. TWC has ordered 50,000 Cyber Sufr cable modems from Motorola, in Mansfield, MA, and another 50,000 units from Toshiba. The company expects to have about 600 to 1000 cable-modem subscribers in the Akron/Canton deployment. According to Vecchi, the Akron/Canton systems have been upgraded and chosen for deployment with Road Runner service because those systems cover almost all of TWC`s 200,000 subscribers in the area.

The cable modems are installed by TWC. A local vendor installs a hard-disk card in the computer as well as an Ethernet card so that the computer can take advantage of the speeds coming off the network via the modem. A TWC crew then goes out and lays a branch line to the PC and hooks it up to the modem.

Back channel headache

Vecchi cautions that noise or ingress problems still require attention when up grading the system. Every point in the system where there is a tap or a trap, or where any other kind of connector is inserted, has to be checked. That includes house wiring. The basic requirement for cable-modem service is a 750-MH¥network; the second requirement is a clean return path.

Those factors are why TWC has opted for a maximum of 500 homes per fiber node. With larger node sizes, large amplifier cascades are necessary to support those homes. These amplifiers can accumulate more noise. In addition, the downstream and upstream amplifiers must be aligned properly; leakage from bad connectors or cables must be checked.

Defective 75-ohm terminators used in open amplifier ports can cause problems if they are not configured properly, says Vecchi. "They can act as rectifiers and send harmonic beeps back into the system."

However, Road Runner is more than high-speed access--it`s a content environment. The Excalibur Group is building a national content service put together in collaboration with Time Inc. New Media. Other types of content optimized for Road Runner include material from Discovery Communications, Warner Music, WB Online, Warner Bros. Studios and independent suppliers of local World Wide Web sites, news and shopping, connections to libraries, schools and government offices. q

Paul Palumbo writes from Seaside, CA.

More in Network Design