10.1 Spectrum Management Background

The goal of the Telecommunications Act of 1996 was to let anyone enter any communications business and to let any communications business compete with any other communications business. This reform would affect telephone service, as we know it, namely, local and long distance service, cable programming and other video services, broadcast services, and services provided to schools .

Title I of the 1996 Telecom Act has attempted to stimulate increased competition in the provisioning of telecommunications services by opening access to the local exchange and in turn allowing the local exchange carriers (or regional Bell operating companies) to provide manufacturing and long distance service. In exchange for entering manufacturing and long distance businesses, the local exchange carriers must allow unbundled loop access [10].

Prior to the 1996 Telecom Act and after the breakup of the Bell System in 1984, the North American telephone network was divided into two separate entities, the local exchange carriers (LECs) who provide network access and local phone service, and the interexchange carriers (IXCs) who provide long distance service. Generally, the end customer would not have a choice on the network access portion of the phone service; it is the LEC that owns and provides the subscriber line access. However, customers do have a choice of long distance service providers. Generally , the LECs provided switched phone service within their local access and transport area (LATA), also known as intra-LATA service. Later the IXCs began competing with the LECs for providing intra-LATA switching service; however, it was still the LECs who provided access to the local exchange, simply because they are the ones who own the wires.

The U.S. Federal Communications Commission's (FCC) first report and order for loop unbundling was the first step in allowing competition for local access. With competition mandated for local access, two families of companies providing local access were formed : the incumbent local exchange carriers (ILECs) and the competitive local exchange carriers (CLECs). In the United States, the ILECs are the regional Bell operating companies and the independent telephone companies; these are the companies that own the wires in the loop plant. The CLECs are any other communications companies that look to provide competitive local access and communication services to end users. Because the CLECs do not have their own infrastructure of subscriber lines, the ruling of loop unbundling requires the owners of the cable (namely, the ILECs) to lease wire pairs to the competitive access providers (namely, the CLECs).

There are CLECs that provide a full range of telecommunications communications services, namely, voice and data services. There is also another group of competitive access providers that offer only data services, and they are often referred to as data local exchange carriers (DLECs). Further telecommunications service competition is provided by multiple system operators (MSOs), using cable-TV infrastructure for voice and data (cable modem) services, and by wireless data service providers, including both terrestrial- and satellite-based systems.

Digital subscriber lines are generally the means for local exchange carriers (incumbent or competitive) to offer high-speed data services. As we have seen earlier, there are a large variety of DSL-based services available. Generally, the symmetric DSL services are used for business applications and the asymmetric DSL services are for consumer and residential applications. There are exceptions to this generalization, but for the most part business applications require more symmetric transmission configurations and consumer (or residential) applications use more asymmetric transmission configurations.

Because both CLECs and ILECs will deploy service on different wire pairs in the same cable, the signals must be deployed such that the spectral integrity of the cable is maintained . The cable could potentially contain a broad mixture of symmetric and asymmetric DSL services. If not properly managed, the deployment of a broad range of signals in the cable plant can cause significant crosstalk interference into other signals in the same cable, which can cause severe degradation in the quality of service to another customer or that of a competitor. To avoid the situations of severe quality of service degradation, a set of guidelines need to be followed in the deployment of signals with varying spectral characteristics. This is the fundamental basis for having a spectrum management standard.

The spectrum management standard provides the technical specifications to help prevent service trouble resulting from uncontrolled crosstalk. In today's competitive environment, equipment vendors and service providers both desire to provide even higher bit rates to more customer (e.g., longer lines). What is the easiest way to achieve higher bit rates and operation on longer loops ? Transmit a more powerful signal. Without a spectrum management standard, DSL systems would soon escalate transmit power in an effort to "shout louder than everyone else at the party."

The ILEC is both a loop provider and a service provider, because they own the cable infrastructure and provide a service (voice, data, and others) to customers via their subscriber loops. CLECs, on the other hand, generally do not own a cable infrastructure and are therefore only service providers. To provide service, they must lease lines from the loop provider, usually an ILEC. Both the incumbent and competitive access providers must follow the same spectrum management rules when deploying services in this unbundled environment.

In the deployment of DSL services, CLECs (or DLECs) primarily provide competitive access service to business customers. These customers are generally served with a symmetric DSL such as 2B1Q-based SDSL. The same companies will also serve the residential customers with asymmetric services, which would generally be provisioned using ADSL. ILECs also deploy both symmetric and asymmetric services. But for ILECs, a significant deployment of DSL-based services is to residential customers who are provisioned with ADSL. The business customers subscribing to high capacity service are more commonly deployed using HDSL.

With regards to policy making, the spectrum management standard does not define policy for the deployment of the DSL signals in the cable. In the United States, policy making or spectrum management rule making is the job of the FCC. The spectrum management standard would serve as a technical input to the FCC in their procedures for establishing policy for deployments of signals in a cable. Early spectrum management efforts by the FCC were based on a policy of first-in-the-cable, and a transmission was presumed acceptable when shown to have been in service somewhere with no reported troubles. The need for a sound technical basis was recognized, and the FCC requested T1E1.4 to develop a technical standard for spectrum management of local loops. Without the technical rigor of the spectrum management standard, crosstalk problems from a new type of DSL might not be recognized until many thousands of such systems had been placed in service.

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