scope:

For the interrelationships of this Recommendation with other ITU-T G.99x-series Recommendations, see [b-ITU-T G.995.1].

This Recommendation describes the interface between the telecommunication network and the customer installation in terms of their interaction and electrical characteristics. The requirements of this Recommendation apply to a single asymmetric digital subscriber line (ADSL).

ADSL provides a variety of frame bearers in conjunction with other services:

• ADSL service on the same pair with voiceband services (including plain old telephone service (POTS) and voiceband data services). The ADSL service occupies a frequency band above the voiceband service, and is separated from it by filtering.

• ADSL service on the same pair as integrated services digital network (ISDN) service, as defined in Appendices I and II of [ITU-T G.961]. The ADSL service occupies a frequency band above the ISDN service, and is separated from it by filtering.

• ADSL service on the same pair with voiceband services (e.g., POTS and voiceband data services), and with TCM-ISDN services as defined in Appendix III of [ITU-T G.961] on an adjacent pair. The ADSL service occupies a frequency band above the voiceband service, and is separated from it by filtering.

• ADSL service with extended upstream bandwidth on the same pair with voiceband services (including POTS and voiceband data services). The ADSL service occupies a frequency band above the voiceband service, and is separated from it by filtering.

ADSL also provides a variety of frame bearers without baseband services (i.e., POTS or ISDN) being present on the same pair.

• ADSL service on a pair, with improved spectral compatibility with ADSL over POTS present on an adjacent pair.

• ADSL service on a pair, with improved spectral compatibility with ADSL over ISDN present on an adjacent pair.

In the direction from the network operator to the customer premises (i.e., the downstream direction), the frame bearers provided may include low-speed frame bearers and high-speed frame bearers; in the other direction from the customer premises to the central office (i.e., the upstream direction), only low-speed frame bearers are provided.

The transmission system is designed to operate on two-wire twisted metallic copper pairs with mixed gauges. This Recommendation is based on the use of copper pairs without loading coils, but bridged taps are acceptable in all but a few unusual situations.

An overview of digital subscriber line transceivers can be found in [b-ITU-T G.995.1].

Specifically, this Recommendation:

• defines the transmission protocol specific transmission convergence sub-layer for ATM, STM and Packet transport through the frame bearers provided;

• defines the combined options and ranges of the frame bearers provided;

• defines the line code and the spectral composition of the signals transmitted by both ATU-C and ATU-R;

• defines the initialization procedure for both the ATU-C and the ATU-R;

• specifies the transmit signals at both the ATU-C and ATU-R;

• describes the organization of transmitted and received data into frames;

• defines the functions of the operations, administration and management (OAM) channel.

In separate annexes, it also:

• Describes the transmission technique used to support the simultaneous transport of voiceband services and frame bearers (ADSL over POTS, Annex A) on a single twisted-pair.

• Describes the transmission technique used to support the simultaneous transport of ISDN services as defined in Appendices I and II of [ITU-T G.961], and frame bearers (ADSL over ISDN, Annex B) on a single twisted-pair.

• Describes the transmission technique used to support the transport of only frame bearers on a pair, with improved spectral compatibility with ADSL over POTS present on an adjacent pair (all-digital mode, Annex I).

• Describes the transmission technique used to support the transport of only frame bearers on a pair, with improved spectral compatibility with ADSL over ISDN present on adjacent pair (all-digital mode, Annex J).

• Describes the transmission technique used to support the simultaneous transport of voiceband services and frame bearers for extended upstream bandwidth operation (EUADSL2plus over POTS, Annex M) on a single twisted-pair.

This Recommendation defines the minimal set of requirements to provide satisfactory simultaneous transmission between the network and the customer interface of a variety of frame bearers and other services such as POTS or ISDN. This Recommendation permits network providers an expanded use of existing copper facilities. All required physical layer aspects to ensure compatibility between equipment in the network and equipment at a remote location are specified. Equipment may be implemented with additional functions and procedures.