scope:

The requirements of this standard apply to a single digital subscriber line (DSL) consisting of a line termination (LT), a two-wire metallic cable pair, and a network termination (NT) (see clause 3). The transmission system is designed to operate on two-wire twisted metallic cable pairs with mixed gauges.

This standard is based on the use of cables without loading coils, but bridged taps are acceptable with the exception of unusual situations. See 5.4 for a definition of cable plant over which the system should operate.

Specifically, the scope of this standard is as follows:

− it describes the transmission technique used to support full-duplex service on a single twisted-wire pair;

− it specifies both the input signal with which the NT must operate and the output signal that the NT must produce across the U reference point (see figure 2);

− it defines the line code to be used, and the spectral composition of the transmitted signal at the U reference point;

− it describes the electrical and mechanical specifications of the network interface at the U reference point;

− it describes the organization of transmitted data into frames and superframes;

− it defines the functions of the operations channel;

− it describes the maintenance modes of the NT.

Although this standard does not include, except for some aspects of the frame structure, any direct requirements concerning the network side of the interface, such requirements are implied. It shall be understood that the network side conforms to the standard if it interfaces appropriately with any conforming NT or equivalent. Appropriate interfacing shall be understood to mean that the aspects of the network service related to physical characteristics associated with the interface can be provided.

Purpose

This interface standard was written to provide the minimal set of requirements to provide for satisfactory transmission between the network and the NT, while conforming, wherever possible, with the I-Series of the International Telecommunication Union - Telecommunication Standardization Sector (ITU-T) Recommendations, and while not compromising the principles of evolution expressed therein. Equipment may be implemented with additional functions and procedures.

This standard presents the electrical characteristics of the integrated services digital network (ISDN) basic access signal appearing at the network side of the NT. It also describes the physical interface between the network and the NT. The transport medium of the signal is a single twistedwire pair that supports full-duplex (i.e., simultaneous two-way) service.

While this standard is written explicitly to describe the physical interface of the network and the NT, its use in other circumstances, such as equivalent use of NT1 functionalities behind an NT2 (e.g., a PBX) is not prohibited.

Structure

Clause 1 describes the scope, purpose, and structure of this document. Clause 2 lists referenced documents. Clause 3 lists definitions helpful in interpreting the specifications. Clause 4 describes the physical characteristics of the interface over which the transmission method specified in the document in clause 5 is intended to operate. Clause 6 describes the functional characteristics of the transmission method. Clause 7 describes the electrical characteristics of the interface. Clause 8 describes the functions and operating procedures associated with the overhead bits included with the transmitted data. Clause 9 describes the environmental conditions. Information on testing is given in annex A, while information on surge protection and out-of-band energy is given in annex B. Annex C provides information on activation, annex D provides information on linearity measurements, annex E is a discussion on embedded operations channel addressing, and annex F gives supporting information relating to dc metallic termination. Annex G contains tables of primary constants for telephone cable. Annex H gives a description of a method of NT powering using pins of the interface connector. Annex J discusses options that may be appropriate if these requirements are adopted as national standards in countries that require NT powering over the loop. Annex K contains new material describing the digital section. Annex L documents the changes in this revised standard from requirements given in ANSI T1.601-1992. Annex M consists of a bibliography for informative purposes only of related standards and publications.