When FTTC isn't enough:

The telecommunications industry is starting to see the broadband access forest for the trees. Most carriers have decided that hybrid fiber/coax is too problematic and that switched digital services fiber-to-the-curb architecture is the way to go. Some have even suggested that they skip HFC and FTTC and go directly to fiber to the home.

In fact, FTTH looks like the eventual access network of choice when cost targets and power issues are resolved.

The switched digital services FTTC architecture, as good as it is, fails to meet the needs and cost targets of a total service application. It costs about the same as a digital loop carrier system with a copper distribution for new build and rehabilitation projects. But it may not be cost-efficient for scattered demands of second lines and requirements for residential data-such as work at home, high-speed modems and LAN/WAN interfaces-in existing neighborhoods.

The Bell regional holding companies and GTE must address all service requirements to maintain their customer base, but they cannot deploy overlay networks for each service application. A single network architecture platform is needed to provide switched digital services FTTC, scalable optical DLC and a DSL platform.

A single network element in the central office manages all the access nodes in the loop and provides the interface for the network side (Figure 1). The broadband digital terminal can be housed in the CO or in remote areas of concentrated demand.

As the narrowband and broadband services aggregate at the CO, they must interface with either the switch or the network. Locally switched POTS services will interface with the local digital switch via TR-08 or GR-303. Both these standards must be available simultaneously to optimize switch utilization and reduce switch module costs. The demand for multiple switch terminations and handoffs to competitive local exchange carriers and competitive access providers will require virtual remote capability from the same broadband digital terminal.

The terminal also must be able to unbundle traffic, including telephony DS-0s, Internet provider access and video information provider interfaces. It is important that the network elements in the field interface to a single network element at the CO. A unified platform will provide a common single operations support system (OSS) interface to the many operation systems that may be required by each application area. It is also critical that each OSS interface with a common platform to eliminate the need for several individual applications and terminals in the maintenance and control centers.

Each wire center will have a mix of applications that must be addressed. The areas of new growth and rehabilitation will best be served by FTTC using the broadband network unit. The second line and in-home data requirements are best provided over a DLC/Digital subscriber line (DSL) vehicle via the universal services access multiplexer. The business areas also will require a mix of both vehicles to meet their unique demands.

Greenfield FTTC The FTTC access system will be the architecture of choice for new build areas and rehabilitation projects. It provides for the feeder and distribution networks from the CO to the home-serving pole or pedestal.

The cost of deploying FTTC must be equivalent to the cost of next generation DLC and twisted pair distribution. Construction budgets therefore do not need to be increased to meet basic franchise requirements. It also provides a broadband-ready platform. And because the network is fiber to the serving pole or pedestal, maintenance savings are likely, too. The only copper left in the network is the drop. This will end much of the controversy surrounding allegations that telcos cross-subsidize their new media ventures.

Because FTTC systems are broadband-ready, the installation is done correctly from a powering, electronics and fiber perspective so the forklift upgrade of last generation FTTC systems is gone. To move to broadband requires only plug-in cards, and everything else is left intact. This, along with cost, spelled the downfall of the first generation of FTTC systems.

The universal service access multiplexer is a remote terminal that provides access for areas of growth where the copper plant is in reasonably good condition and requires no immediate rehabilitation. A full-service multiplexer architecture will provide for quick DSL deployment and POTS in areas of high second-line demand.

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The access multiplexer provides this opportunity and uses the same CO platform as FTTC, including the operations interfaces. Each wire center will have areas of new build and rehabilitation as well as demand for DSL services to all customers.

The combination of FTTC and the universal access multiplexer can meet the demands economically and requires only one unified platform to administer.

The access multiplexer delivers full-service very-high-speed DSL to the home over typical serving area interface to home distances in the 3 to 4 kilofoot range. This allows full service, including multiple MPEG2 streams and Internet protocol data simultaneously over the same connection, along with POTS at baseband.

The access multiplexer can be used at a carrier serving area or longer lengths of twisted pair to deliver POTS at the baseband and lower speeds using rate adaptive DSL for data applications from a few hundred kilobits per second to more than 6 Mb/s, depending on the distance.

Because the unified platform has interfaces to the local digital switch, including TR-008 and GR-303, the DSL circuits can derive telephone service on the DSL card, eliminating jumpers and simplifying the diplex filters required to combine DSL with POTS.

This can save money, simplify maintenance and troubleshooting and ease the jumpers' recordkeeping when diplex filters are inserted into the POTS path.

No catastrophe needed The key to routing the potentially devastating load of Internet traffic is to send traffic with no need to be switched directly to the service provider. It's important to address this on a wire center basis with a single network element that can optimize applications-DLC, DSL and FTTC-to ensure maximum use of the network and relief to the local switch.

Traffic destined for the Internet service provider is routed by the broadband digital terminal to the appropriate trunk group or asynchronous transfer mode switch. Full switching capability at the terminal is necessary so traffic can fully access any output port for routing or switching (Figure 2).

The single CO platform can address the entire wire center and provide the network access to meet service requirements ranging from telephony switching to high-speed data to video information providers.

This does not come without drawbacks such as extra power requirements. Power has been the Achilles heel of the loop from the time electronics were first put in the field. Unlike CATV and alternative access providers, the Bell companies always have powered the system, including the customer premises requirement, to provide continuous lifeline service. The power problem only worsens when broadband power requirements are added to the equation.

A state-of-the-art power system tied to a state-of-the-art access system is required. The access system needs to shut down non-essential services so it will consume less power during prolonged outages. The power system must monitor the batteries or gas backup generators to ensure that at least eight hours of standby reserve will be available. The power system also must serve more broadband network units to be economically viable and easy to manage (Figure 3).

Today's work force cannot afford to be saddled with maintaining many power nodes during power service interruptions, such as hurricanes, ice storms and El Nino-related conditions.

Final fiber frontier The final frontier for the full service access network is the gateway into the home. In-home wiring and the need to interface with multiple elements within the home requires a gateway that will address all residential needs. These have changed during the past few years and will continue to evolve.

With work-at-home data needs, Internet access and videoconferencing options, homes are starting to look like businesses. Residential services will require more and more bandwidth to meet the anticipated demand.

The cost of the equivalent of the traditional set-top box must be driven down. That can be done by consolidating multiple digital video decoders and a data modem into one gateway box.

Because much of the cost of a set-top box or data modem comes from the enclosure, power supply, processor, memory and common elements, cost can be reduced by 50% or more by sharing the common elements. This makes an all-digital solution cost-competitive with an analog CATV system.

The residential gateway can meet these needs and cut the number of costly terminals. The gateway requires one network interface to interconnect with any in-home device, dramatically reducing the network cost.

The service modules can be added as service demands dictate. The analog video, switched digital video and home management systems are controlled from one wireless remote.

Ethernet-based Internet access and narrowband services can be connected through the gateway. Many variations and options are possible in the gateway, ranging from a cost-effective digital video and data terminal up to and including a more open and flexible box.

The picture painted here is not an architecture that can wait for the future. It can be offered today to ensure a "future-proof" network for services now in demand. Equipment providers are required to provide and manage large-scale deployments. This may be impossible without a unified platform, and could result in costly and unmanageable overlay networks. This would give the CATV industry an advantage because it can consolidate services on one access platform, albeit a less capable broadcast network.

Islands of technology will be the dinosaurs of the industry soon. Large-scale deployments will be impossible without adherence to standards and interoperability requirements.

It has taken many years, but technology and standards are now at a level where LECs can leverage their embedded twisted pair networks for broadband (Figure 4). The valuable twisted pair network can be upgraded with a fiber-based, switched FTTC system, resulting in a ubiquitous, cost-effective, manageable and uniform full service network.