Nortel Networks Circuit Card 311 - Manual (Page 366)

366 NT5K21 XMFC/MFE card
• 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 163 "MFC Frequency values" (page 366) lists the frequency values
used for forward and backward signals.
Table 163
MFC Frequency values
Digit
Forward direction
DOD-Tx, DID-Rx
backward direction
DOD-Rx, DID-Tx
1 1380 Hz + 1500 Hz 1140 Hz + 1020 Hz
2 1380 Hz + 1620 Hz 1140 Hz + 900 Hz
3 1500 Hz + 1620 Hz 1020 Hz + 900 Hz
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
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