Nortel Networks Circuit Card - Manual (Page 646)

Page 646 of 906 NT8D15 E&M Trunk card
553-3001-211 Standard 3.00 August 2005
for a tandem connection where the originating end is senderized and the route
is over a CO trunk (CCSA not applicable).
Type II signaling uses four leads: M, SB, E, and SG. Instead of changes of
state between battery and ground (M signals) or open and ground (E signals),
the trunk signals by closing the contacts between the lead pairs M and SB.
Signals are received by detecting current flow between lead pairs E and SG.
On incoming calls, the far end seizes the trunk by shorting the E and SG leads
together. This transmits the ground from the SG lead to the E lead (in Type I
signaling the ground to the E lead comes from the far-end). Dialing is done
by opening and closing the E/SG contacts. Since the SB and M leads are also
used as the ESCG and ESC leads, respectively, for echo suppression, echo
suppressor control cannot be used with Type II signaling.
Note: M, SB, E, and SG designations are Electronic Industries
Association and Telecommunications Industries Association (EIA/TIA)
conventions. These leads are also known as MB, MA, EA, and EB,
respectively.
Release control
Release control of a call made over a trunk is specified in LD 16. Disconnect
supervision is specified for each trunk group independently. The two options
available are EITHER or ORIGINATING party control. These can be
specified for the end (near-end), or for the central office or other PBX end
(far-end). Joint party control can also be specified for the far-end.
Duplex signaling
Duplex (DX) signaling makes use of the voice transmission leads for
signaling as well as for voice transmission.
For descriptive purposes, the lead pair Tip B/Ring B is designated the
signaling pair. The other pair Tip A/Ring A conducts current in the opposite
direction to balance the overall current flow between the near and far ends.
During signaling, current flows through both Tip B and Ring B leads in the
same direction.