ITU-T G.998.4 PDF

This Recommendation specifies techniques beyond those defined in the existing ITU-T digital subscriber line (DSL) [ITU-T G.992.3], [ITU-T G.992.5] and [ITU-T G.993.2] to provide enhanced protection against impulse noise or to increase the efficiency of providing impulse noise protection (INP).

Impulse noise is a noise event of limited duration that can degrade one or more transmitted symbols. Unlike the various types of continuous noise found on DSLs, impulse noise has a short duration and may repeat, either randomly or periodically. Impulse noise that does not appear to repeat periodically but occurs as unpredictable events is termed SHINE (single high impulse noise event). Impulse noise caused by noise from electrical mains and that thus repeats at a constant period related to the local AC power frequency is termed REIN (repetitive electrical impulse noise).

Impulse noise protection techniques are, in general, techniques used by a DSL transceiver to protect against the effects of impulse noise on the transmitted signal. Existing ITU-T DSL Recommendations specify techniques to ameliorate impulse noise effects. Among these methods are the use of forward error correction (FEC) coding and interleaving.

This Recommendation specifies a physical layer retransmission method for enhancing INP, with annexes specifically providing the details required for implementation of these techniques for transceivers supporting [ITU-T G.992.3], [ITU-T G.992.5] and [ITU-T G.993.2]. Methods for enhancing INP by techniques other than physical layer retransmission are for further study.