3Com SuperStack 3 NBX Administrator's Manual page 295

3 From the Select Device Type pull-down list, select T1 Span List.
4 Click Apply.
5 Select the span for which you want to set echo cancellation.
6 Click the Audio Controls button. See Figure 117.
Figure 117 Audio Controls for a T1 Digital Line Card
7 Enable the Echo Canceller Enabled check box to turn on echo
cancellation.
8 Click OK.
Configuring and Managing T1 Digital Line Cards 295