A multi-unit test system performs automated and dynamically alterable,
double-ended testing of telephone lines, whose service is provided on
copper cable pairs. A prescribed set of (e.g., twelve) individual tests
are executed either from a hand-held measurement unit, or by a central
office-resident direct access test unit, or by a collaboration of the
two. The hand-held measurement unit and the direct access test unit
exchange FSK-based test control messages with one another that are
effective to cause a selected electrical condition to be applied to a
first portion of the wireline and to cause a prescribed electrical
measurement to be made at a second portion of the wireline.