G9923

G.992.3 is an ITU-T recommendation that defines ADSL2, the second-generation asymmetrical digital subscriber line technology for use over standard copper telephone lines. It extends the capabilities of the original ADSL specifications (such as G.992.1) by enabling higher data rates, improved spectral efficiency, and better performance on a wider range of loop conditions. The standard specifies the physical layer, training procedures, and modulation methods used by both ends of an ADSL link, and is designed to be backward compatible with earlier ADSL implementations.

Key features of G.992.3 include enhanced multi-tone modulation and more efficient use of the available frequency spectrum, which together support higher downstream and upstream rates on many copper pairs. It also improves resilience to certain types of line noise and allows for optional enhancements that can increase upstream capacity, such as Annex M. The standard defines multiple annexes to accommodate regional regulatory and deployment requirements, enabling operators to tailor the technology to local conditions while maintaining interoperability.

Deployment and operation rely on existing DSLAM equipment at the service provider and customer premises equipment at the user end, connected over the common copper loop. G.992.3 is commonly deployed alongside later DSL standards, such as G.992.5 (ADSL2+), which further extend possible speeds in suitable scenarios.

Limitations depend on physical line characteristics, including loop length, copper gauge, and noise environment. As with other DSL technologies, performance degrades with longer or poorer-quality lines, and service guarantees are typically expressed as a range rather than a fixed rate.