Page400 of 544 NT5K21XMFC/MFE card
553-3011-100 Standard14.00 January 2002
Signaling levels
MFC signaling uses pairs of frequencies to represent digits, and is divided
into two levels:
Level 1: used when a call is first established and may be used to send the
dialed digits.
Level 2: used after Level 1 signaling is completed and may contain such
information as the status, capabilities, or classifications of both calling
parties.
Forward and backward signals
When one NT5K21 XMFC/MFE card sends a pair of frequencies to a
receiving XMFC/MFE card (forward signaling), the receiving XMFC/MFE
card must respond by sending a different set of frequencies back to the
originating XMFC/MFE card (backward signaling). In other words, the
receiving card is always “compelled” to respond to the originating card.
In summary, the signaling works as follows:
•The first XMFC/MFE card sends a forward signal to the second card.
•The second card hears the forward signal and replies with a backward
signal.
•The first card hears the backward signal and “turns off” its forward
signal.
•The second card hears the forward signal being removed and removes its
backward signal.
•The first XMFC/MFE can either send a second signal or drop out of the
call.