Nortel Networks 553-3001-211 manual Signaling levels, Forward and backward signals

Page 358 of 894 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.

553-3001-211 Standard 2.00 September 2004