British cable-TV operators resist the installation of fiber to the home
DAVE WILSON
The development of residential access networks in the United Kingdom during the next few years will undoubtedly be driven by customer demands for new revenue-generating broadband services. Until the cable companies fully understand what those demands are, however, it will be difficult to predict the route that fiber might travel to the home. Presently, British cable-TV companies have enough bandwidth capacity to cope with such demands by installing hybrid fiber/coaxial-cable network solutions.
But is fiber to the home a necessity or a money-spinning idea conjured by the telecommunications operators and the fiber-optic cable and opto-electronic component suppliers?
According to Hugo Davenport, chairman of U.K.-based Cambridge Cable, "The fiber-to-the-home debate has nothing to do with performance. It has to do with the existing twisted-pair setu¥of telecommunications operators. The only obvious way for them to go is fiber-optic, because they have the duct capacity already in place."
But it is not an obvious route for cable-TV companies to take. For them, a hybrid fiber/coaxial-cable solution might perform just as well. One U.K. cable-TV network run by Telewest Communications` owned-and-operated franchises uses vestigial sideband, amplitude-modulated fiber techniques to deliver television signals to a dedicated hub. Currently, economics dictate that these hubs pass approximately 525 homes. From the fiber hub, a standard cable-TV distribution network that comprises coaxial cable and radio-frequency amplifiers carry the signals to the homes.
The available bandwidth delivered to customers in this network is 750 megahertz. The network apportions 5 to 40 MH¥in the reverse direction for digital, interactive and monitoring services; 50 to 550 MH¥for forward transmission of analog video; and 600 to 750 MH¥for forward direction digital services.
Only a few people need more bandwidth than that, according to Davenport. "It is difficult to see how an average household is going to use more than 1 gigahert¥of bandwidth. There is only one activity that might conceivably require us to provide more bandwidth, and that`s if genetic engineering becomes a popular hobby at home," he contends.
In addition, the installation of fiber to the home is expensive in terms of the investment that cable-TV companies and network operators have to make. According to Gary Baker at Alcatel Network Systems in the United Kingdom, 43 million twisted pairs of copper radiate from 7500 local exchanges in the United Kingdom.
Fiber replacement
Industry analysts estimate that fiber replacement would cost $18.2 billion, primarily resulting from the high prices of opto-electronic interfaces, detectors and transmitters. The payback for such an immense investment would typically take seven or eight years.
One of the benefits of fiber to the home is that the bandwidth provided is symmetric. Fiber solutions provide as much upstream bandwidth as downstream. This capacity should prove useful for such future services as videoconferencing.
Most cable-TV services today, however, require limited upstream bandwidth; there is little need for traffic moving from the subscriber back to the headend. In addition, the hybrid fiber/coaxial-cable networks are capable of delivering enough bandwidth downstream as well as lower bandwidth upstream to meet present customer needs.
Last year, for example, U.S.-based Broadband Technologies upgraded its fiber-to-the-curb loop-access system to support more than 1500 channels of interactive video programming.
Whether cable-TV operators need to go beyond 750 MH¥in the short term is questionable. But in the long term, end users could act as servers in their own right. Consumers are expected to have several information-handling devices--interactive television sets and personal computers--in the home, all supported by an interface into the access network. Such applications as video telephony or teleworking will demand additional bandwidth, especially in the upstream bandwidth direction.
If more than a 1-GH¥bandwidth is required, the home environment will not support the radio-frequency cause. If several household devices, including television sets and personal computers, have to be connected into an internal cable home network, users would experience losses from RF connectors. Similarly, cable-TV operators would experience problems from noise ingress into the network from each home.
No fiber problems
Fiber-optic cables, of course, would not have such problems. Fiber-optic systems present a natural barrier to such noise because signals are transferred to and from the optical and electrical domains.
Vendors of RF systems would find that signal losses greater than 1 GH¥are unacceptable. Most observers agree cable-TV operators cannot run beyond a 1-GH¥bandwidth. At that bandwidth, component design and cost prove difficult and expensive.
Consequently, cable-TV operators face a natural limit to the amount of bandwidth cable can deliver. But is it necessary to bring fiber all the way to the home to deliver advanced broadband services to the customer? Many cable-TV companies can perform that function easily enough by replacing their existing analog systems with fiber-optic digital solutions.
In the United Kingdom, such companies as Yorkshire Cable are installing synchronous digital hierarchy equipment made by Northern Telecom to provide future bandwidth on demand. The SDH platform will permit the introduction of asynchronous transfer mode switches into the network and enable Yorkshire Cable to launch future broadband services. Similarly, such operators as Cambridge Cable (that uses an AM-VSB system) are performing field trials of a fiber-to-the-curb/coaxial-cable network-to-the-home system that will offer packet-switched digital data via an ATM switch.
"Fiber to the curb is adequate for functional purposes. It is difficult to see why you would need fiber to the home. We are demonstrating the feasibility of running a packet-switched network to deliver wide bandwidth digital data, not just for entertainment-TV, but for data services, too. We are assuming such a system will require symmetrical bandwidth to support people working from home," says Davenport.
And if the capacity needs to be increased, cable-TV operators could add a second coaxial cable, or shadow, system onto their hybrid fiber/coaxial-cable networks. The shadow system would allow operators to transmit downstream on one coaxial cable, and upstream on the other.
The addition of a second coaxial cable would not be difficult or costly. Some U.K. cable-TV operators are already installing telephony overlays by using standard twisted pairs of copper for the final drop, thereby providing a twisted-pair and a coaxial cable into the home. q
Dave Wilson writes from London.