AOpen FM56 Manual page 61

Reporting Supported Range of Parameter Values
Command: +MR=?
Response: +MR: (<value>range)
Example: +MR: (0,1)
The format of this information text is:
+MCR: Report Syntax
Response: +MCR: <carrier>
<carrier> Alphanumeric code corresponding to the reported carrier. Defined values are:
B103 For Bell 103
B212 For Bell 212
V21 For V.21
V22 For V.22
V22B For V.22bis
V23C For V.23
V32 For V.32
V32B For V.32bis
V34 For V.34
K56FLEX For K56flex
+MRR: Report Syntax
Response: +MRR: <tx_rate>,<rx_rate>
<tx_rate> Decimal transmit rate in bits/s.
<rx_rate> Decimal receive rate in bits/s.
Example: +MRR: 28600, 48000