Nortel Enterprise 1000 Reference Manual page 62

Page 62 of 236 Analog Trunk Cards - NT8D14 Universal Trunk Card
Figure 18
Loop start call connection sequence
A
Near-end
Succession
CSE 1000
State
Idle
Call request
Outpulsing
B rings
B answers
(2-way voice
connection)
B goes on hook
Idle
A goes on hook
Idle
553-3023-211 Standard 1.00 June 2001
Signal/direction
Ground
High-resistance
loop
Low-resistance loop
Dial tone
Address signaling
Ringback
Low-
resistance Polarity reversal
loop or normal battery
Ground on tip/
battery on ring
High-resistance loop
High-resistance loop
Ground on tip/
battery on ring
Far-end
CO
on tip/
battery
on ring
When trunk access code is dialed by a station or
attendant, the near-end replaces the high-resistance
loop with a low-resistance loop and removes the ring
detector from the circuit.
CO detects low-resistance loop and returns dial tone.
Near-end applies addressing to the trunk in the form of
loop pulses or DTMF tones. Upon receipt of the first
pulse/tone at the CO, dial tone is removed.
Upon completion of outpulsing, the call is forwarded
through the public network and B is rung (if idle) and
the appropriate audible indication is returned.
When B answers, the CO reverses polarity of the tip and
ring leads. The polarity reversal is detected by the near-
end and end-of-dialing is assumed, if it has not already
been received, and the trunk is considered to be in the
talking state. If answer supervision is not detected after a
maximum of 15 seconds from last dialed digit, end-of-
dialing is assumed by the near-end.
If far-end disconnects first, CO restores normal battery
and ground on tip and ring and may apply either a dial
tone or a busy tone.
Near-end detects restoration of normal battery and
ground and opens loop.
If near-end disconnects first, it restores a high-resistance
loop.
Far-end detects drop in loop current and restores
normal battery and ground on tip and ring.
B
Remarks
553-CSE6239