Recommendation ITU-T G.992.3 describes asymmetric digital subscriber line (ADSL) transceivers on a metallic twisted pair that allows high‑speed data transmission between the network operator end (ATU‑C) and the customer end (ATU‑R). It defines a variety of frame bearers in conjunction with one of two other services, or without underlying service, dependent on the environment:
1) ADSL transmission simultaneously on the same pair with voiceband service.
2) ADSL transmission simultaneously on the same pair with integrated services digital network (ISDN) (Appendix I or II of Recommendation ITU-T G.961) services.
3) ADSL transmission without underlying service, optimized for deployment with ADSL over voiceband service in the same binder cable.
4) ADSL transmission without underlying service, optimized for deployment with ADSL over ISDN service in the same binder cable.
5) ADSL transmission with specific requirements for Reach Extended ADSL2, simultaneously on the same pair with voiceband service.
6) ADSL transmission with extended upstream bandwidth, simultaneously on the same pair with voiceband service.
7) ADSL transmission on the same pair with voiceband services and operating in an environment with TCM‑ISDN (Appendix III of Recommendation ITU-T G.961) services in an adjacent pair.
This Recommendation specifies the physical layer characteristics of the asymmetric digital subscriber line (ADSL) interface to metallic loops.
This Recommendation has been written to help ensure the proper interfacing and interworking of ADSL transmission units at the customer end (ATU‑R) and at the network operator end (ATU‑C), and also to define the transport capability of the units. Proper operation shall be ensured when these two units are manufactured and provided independently. A single twisted pair of telephone wires is used to connect the ATU‑C to the ATU‑R. The ADSL transmission units must deal with a variety of wire pair characteristics and typical impairments (e.g., crosstalk and noise).
An ADSL transmission unit can simultaneously convey all of the following: a number of downstream frame bearers; a number of upstream frame bearers; a baseband plain old telephone service (POTS)/ISDN duplex channel; and ADSL line overhead for framing, error control, operations, and maintenance. Systems support a net data rate ranging up to a minimum of 8 Mbit/s downstream and 800 kbit/s upstream. Support of net data rates above 8 Mbit/s downstream and support of net data rates above 800 kbit/s upstream are optional.
This Recommendation defines several optional capabilities and features:
• transport of STM and/or ATM and/or Packets;
• transport of a network timing reference;
• multiple latency paths;
• multiple frame bearers;