AT&T MERLIN LEGEND Installation & Maintenance Manual page 51

System Description
Touch-Tone Receivers
The 800 DID, 008 OPT, and 012 modules each provide two
TTRs. Normally these TTRs are sufficient to handle calls
originated on the 012 or 008 OPT module or received on the 800
DID module. However, additional TTRs maybe needed to
support the following services:
tie trunks and DS1 emulated tie trunks set for Dual-Tone
Multifrequency (DTMF) signaling
Remote Access
Account Code Entry
AUDIX Voice Power (AVP)—IS II or Integrated Voice Power
Automated Attendant (IVP AA)—IS II applications
If more TTRs are needed to support these services, 400 or 400
GS/LS/TTR modules can be added (each module provides four
TTRs). Table 1-2 shows the estimated number of TTRs needed in
the system, depending on the call volume and the types of
services.
1-20 Control Unit