Found this logged on an MCD running 12.0.3.15:
TRAFFIC CONGESTION REPORT FROM 16 : 36 TO 20 : 41 Fault count : No Receivers available : 01
What is a Receiver, and what are the consequences of it being congested?
Receivers are used to generate and interpret DTMF digits, detect dial tone and other call progress tones, etc.
The consequences could vary depending on the length that no receivers are available and call volume. The system would not be able to generate DTMF digits for outgoing calls on Loop Start or D4 T1 in-band signaling calls (PRI and SIP would not be effected), the system would not be able to interpret DTMF digits from single line analog devices (dial an extension or outside number and the system can't see the digits dialed), or inbound calls on in-band signalling D4 T1 would not complete as the system could not interpret the DTMF digits.
I believe DTMF receivers also generate dial tone for analog devices, but I am not positive on that one.