Cisco Certified ExpertPower Cutback and Power Boost
Power can be reduced during the train-up sequence when DSL modems calculate and exchange information regarding attenuation. This is part of Cisco's RADSL train-up process. And although you can increase power above a nominal level, this is not commonly done because of the interference imposed on other services in the same cable. This is often referred to as crosstalk between cable pairs, and results in a degraded SNR.
The ability to change the default transmit power level becomes important when comparing different DSL vendors, or when comparing different DSL chipsets. If a system is set to transmit at an abnormally high DSL power level, it might offer exceptionally good reach and noise margin while inducing excessive noise in adjacent cable pairs. During competitive evaluations, some equipment manufacturers increase power to improve reach and noise (bit error) performance. The same transmit levels cannot be deployed in a production telephone company (telco) environment.
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