End-to-End DSL Architectures

Overcoming Impairments

This section covers common techniques used to overcome impairments or at least compensate for them:

• Automatic rate adaptation

• Two latency paths for different traffic types

• SNR (Signal-to-Noise Ratio) margin

• Loop testing

Automatic Rate Adaptation

A rate-adaptive digital subscriber line (RADSL) varies the achieved bit rate according to line quality and distance. This mass deployment technology preserves reach as the rate adjusts to local loop conditions if possible. The term RADSL was first applied to CAP modulation when it was discovered that with a bit of engineering, CAP would retrain (resynchronize) its bit rate systematically downward from the provisioned speed in response to impairments until it achieved a bit rate at ...