A digital subscriber line (DSL) compatible plain old telephone service (POTS)
line
card that interface a telecommunications switching system to a subscriber over
a two-wire subscriber line, wherein the subscriber line card detects whether a
DSL line card is connected to the subscriber line. A digital signal processor on
the POTS line card is configured to process voice-band signals with a first set
of parameters if a DSL line card is connected to the subscriber line and to process
voice-band signals with a second set of parameters if the DSL line card is not
connected to the subscriber line. Detecting the presence of a DSL line card may
be performed by sending a voice band tone on the subscriber line and the return
loss measured. Additionally, a tone above voice band may be sent on the subscriber
line and a return loss measured. The first set of parameters adjust frequency response
of the subscriber line, return loss of the subscriber line and/or trans-hybrid
loss of the POTS line card to compensate for the presence or absence of a DSL card
connected to the subsource line.
