FYI.

In Verizon service areas, and possibly AT&T and Quest, the Westell mounting used with T1 & DDS circuit installations have a slide switch that configures a selectable RJ48C or RJ48S interface on the built in eight pin modular jacks provided.

RJ48C DS1 services on pins: 1-2 (CPE RX) & 4-5 (CPE TX)

RJ48S All DDS rates on pins: 1-2 (CPE TX) & 7-8 (CPE RX)