Nortel Networks 553-3001-211 manual Incoming calls

NT1R20 Off-Premise Station Analog Line card Page 167 of 894

Incoming calls

Incoming calls to a telephone connected to the NT1R20 OPS analog line card originate from stations that can be local (served by the PBX) or remote (served through the public switched telephone network). The alerting signal to telephones is 20 Hz (nominal) ringing. When an incoming call is answered, ringing is tripped as the telephone goes off-hook, placing a low-resistance dc loop across the tip and ring leads toward the OPS analog line card. (see Table 67).

Table 67

Call connection sequence—near-end station receiving call (Part 1 of 2)

	Signal / Direction
State	Far-end / Near-end	Remarks
Line card unit idle	Group on tip, battery on ring	No battery current drawn.
	High resistance loop	Far-end station goes off-hook and
		addresses (dials-up) the near-end
		station. The system receives the
		incoming call on a trunk and determine
		the TN.
Incoming call	Ringing	The system applies 20 Hz ringing to ring
		lead.
Near-end station	Low resistance loop
off-hook
Two-way voice		The system detects increase in loop
connection		current, tips ringing, and put call through
		to near-end station.
Near end station	High-resistance loop	If near end station hangs-up first, the
hangs up first		line card detects the drop in loop
		current.
Line card unit idle	Group on tip, battery on ring	Line card unit is ready for the next call.
	High resistance loop

Circuit Card Description and Installation