/mcpCED (Called terminal identification) – a 2100 Hz signal that is transmitted by the termination fax device upon answering a fax call. This signal temporarily disables echo cancellers that are present on the connection to prepare the line for data transmission. • CFR (Confirmation To Receive) – a response that confirms that the previous messaging and training has been completed and that fax page transmission can begin. • CNG (Calling Tone) – an 1100 Hz tone that is on for half a second and then off for 3 seconds. This signal identifies the fax terminal as a non-speech device. The signal also indicates that the initiating fax terminal awaits the DIS signal from the termination fax terminal. • CRP (Command Repeat) – a response that indicates that the previous command was received in error and needs to be repeated. (Optional) • CSI (Called Subscriber Identification) – is used to provide the specific identity of the called fax terminal through its international telephone number. (Optional) • DCN (Disconnect) – ends the fax call and requires no response. • DIS (Digital Identification Signal) – identifies the capabilities of the called fax terminal. • DTC (Digital Transmit Command) – the response to the capabilities identified by the DIS signal. Here is where the calling fax terminal matches its capabilities with the ones provided in the DIS message of the called fax terminal. • EOM (End Of Message) – indicates the end of a complete page of fax information. • EOP (End Of Procedure) – indicates the end of a complete page of fax information and no further pages are to be sent. Proceed to the disconnect phase of the fax call. • FTT (Failure To Train) – used to reject a training signal and request a retrain (the retrains usually occur at lower modulation speeds). • MCF (Message Confirmation) – indicates that a message has been satisfactorily received. • MPS (MultiPage Signal) – indicates the end of a complete page of fax information and that the receiver is ready for additional pages. • NSF (Non-Standard Facilities) – is used to identify specific capabilities or requirements that are not covered by the T-series specifications. (Optional) • RTN (Retrain Negative) – indicates that a previous message has not been satisfactorily received. Retraining is needed to proceed (usually at a lower modulation speed). • RTP (Retrain Positive) – indicates that a complete message has been received and that possible additional messages ensue after retraining. • TCF (Training Check) – sent through the higher-speed T.4 modulation system (versus the 300 kbps V.21 modulation used for the previous T.30 signaling) to verify training and indicate the acceptability of fax pages sent at this transmission rate. • TSI (Transmitting Subscriber Identification) – indicates the identification of the transmission (calling) fax terminal. (Optional) • Fax Relay Debug Commands