8.3 Unbundling | DSL Advances

In the United States, the Telecommunications Act of 1996 required ILECs to lease unbundled network elements (UNEs) to certified CLECs. The UNEs include:

Lines from the CO to the customer
Lines from accessible remote network sites to the customer (subloops)
Spare fiber facilities (sometimes called "dark fiber")
Inside wire owed by ILEC
Interoffice transmission facilities (trunks), including shared transport
Floor space within the CO where a CLEC may place transmission, switching, and other types of equipment provided it meets the safety, fire, and heat dissipation requirements known as NEBS (Network Equipment Building Standard)
Telephone numbers , including number portability database
Network interface device (NID) demarcation point at customer site
Access to operational support systems (OSSs) and network data bases, including subscriber line qualification data from LFACS (loop facilities assignment system) (see Section 8.6)
SS7 signaling facilities and advanced intelligent network databases
Local circuit switch line ports

On March 31, 1999, the FCC released the First Report and Order CC Docket 98-147 with detailed rules for collocation, and gave notice of future proposed rule making relating to spectrum compatibility and line sharing. Each of the UNEs must be available separately and at a price that is approximately equal to the cost to the ILEC (know as TELRIC pricing ”total element long range incremental cost). In the event that the requested facilities are not available, the ILEC is not required to build additional facilities unless the CLEC pays for the additional cost. Safeguards exist to allow verification of ILEC claims that spare facilities do not exist, in particular CO collocation space. At the CLEC's preference, the ILEC must provide collocation space with or without locked equipment cages that would restrict access to the CLEC equipment. Collocation may be physical (CLEC maintains the equipment) or virtual (ILEC is paid to maintain the equipment on behalf of the CLEC). In both cases, the CLEC must pay to lease the space. The ILEC may apply environmental and safety standards ( generally known as NEBS) to the CLEC equipment that are no stricter than the ILEC applies to its own equipment. CLECs may also locate equipment in a site outside the CO. For DSL systems, it is desirable for the DSLAM to be as close as possible to the MDF (main distributing frame) in the CO to minimize additional line length.

The unbundled subscriber lines are provided for the exclusive use of the CLEC; in the next section, line sharing is discussed. Unbundled lines typically are categorized by transmission technology, for example:

Telephone service capable lines
ISDN capable lines
ADSL capable lines
HDSL capable lines
Lines capable of SDSL or SHDSL at certain bit rates

Carriers who connect equipment to unbundled lines are required by the ILEC to meet spectrum management specifications that limit the effects of crossstalk caused by the transmission system. These requirements apply to equipment at both ends of the line, and include total transmitted power, power spectral density, transverse balance, and longitudinal output voltage. Many types of transmission systems are limited to a maximum line length because the effects of crosstalk are more critical for systems that must also deal with a large amount of attenuation. Chapters 10 and 11 discuss spectrum management in depth.

Unbundled DSL capable lines consist of a direct copper path from the central office main distributing frame (MDF) to the point of network demarcation at the customer premises (generally the NID), and do not include electronics such as line-terminating equipment, repeaters, or digital loop carrier. Telephone-grade unbundled lines may include loading coils, and may be either a direct copper line or a DLC channel connected to a copper sub-loop. Unbundled access via digital loop carrier is discussed further in Section 8.5.

The Telecom Act of 1996 and subsequent FCC Orders prohibit ILECs from directly providing high-speed data services (other than ISDN) to customers. However, the ILEC may create separate subsidiary companies that provide high-speed data service via DSLAMs and data switches owned by the subsidiary. These subsidiaries are treated much like a CLEC; they are not required to provide unbundled DSLAM access or other elements to CLECs.

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