SDSL systems are EC systems and therefore, are disturbed the most by SNEXT. In fact, SNEXT is the dominating disturber to SDSL. The wider the signal bandwidth, the greater the level of SNEXT. The bit rate of the signal is directly proportional to the signal bandwidth, so the reach of SDSL systems decrease with increasing bandwidth (hence, increasing bit rate). Figure 7 shows the reach of SDSL systems relative to SNEXT. Note the decrease in reach with increasing bit rate.

Figure 7. SDSL Reach versus 49–SNEXTs

Because SDSL performance is limited by SNEXT, NEXT from other DSL do have as much impact on SDSL reach. However, depending on the signal bandwidth, SDSL systems may impact the performance of other DSL systems such as ADSL or CAP RADSL. The spectral compatibility of SDSL into other systems is discussed in the subsequent sections. In summary, SNEXT is the dominant disturber into SDSL.