Signaling Levels; Forward And Backward Signals - Avaya Nortel Communication Server 1000 Reference

NT5K21 XMFC/MFE card

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.
MFC signaling involves two or more levels of forward signals and two or more levels of
backward signals. Separate sets of frequencies are used for forward and backward signals:
• Forward signals. Level I forward signals are dialed address digits that identify the called
party. Subsequent levels of forward signals describe the category (Class of Service) of
the calling party, and may include the calling party status and identity.
• Backward signals. Level I backward signals (designated "A") respond to Level I forward
signals. Subsequent levels of backward signals (B, C, and so on) describe the status of
the called party.
Table 135: MFC Frequency values
and backward signals.
Table 135: MFC Frequency values
Digit
1
2
296 Circuit Card Reference
on page 296 lists the frequency values used for forward
Forward direction DOD-Tx, DID-
Rx
1380 Hz + 1500 Hz
1380 Hz + 1620 Hz
Comments? infodev@avaya.com
backward direction DOD-Rx, DID-
Tx
1140 Hz + 1020 Hz
1140 Hz + 900 Hz
July 2011