Nortel Express Installation Manual page 20

If there is no DSP card inserted in slot D1, TNs 8 through 15 cannot be
used for Voice Services. Similarly, if there is no DSP card inserted in slot D2,
TNs 16 through 23 cannot be used for Voice Services. The configurations
supported for units 0–23 are provided in the following table:
DSP
On-board (always available)
Card # 1 (Faceplate Slot D1:)
Card # 2 (Faceplate Slot D2:)
TNs available
0–7
8–15
16–23