Nortel NT1R20 Description page 60

Page 36 of 290 Description
Figure 13
Call connection sequence—near-end originating call
Far-end
station
through
PSTN
State
Line card unit idle
Call request
Outpulsing
(2-way voice
connection)
Near-end station
on hook
Line card unit idle
Far-end station
on hook
Line card unit idle
553-3001-105 Standard 5.00 June 1999
Meridian 1
Signal/direction
Ground on tip/ resistance
battery on ring
Low-resistance loop
Dial tone
Addressing signals
Dial tone
Ringback (or busy)
High-resistance loop
Ground on tip/
resistance
battery on ring
High-resistance loop
resistance
Ground on tip/
battery on ring
Near-end
station
Remarks
High-
loop
No battery current drawn.
Near-end station goes off hook. Battery current
is drawn causing detection of off-hook state.
CPU determines unit terminal number (TN) and
assigns message timeslots.
Dial tone is applied to the near-end station from
the Meridian 1.
Near-end station dials number (loop pulsing or
DTMF tones).
Meridian 1 detects start of dialing and
removes dial tone.
Meridian 1 decodes addressing, routes call, and
supplies ringback tone to near-end station if far-
end station is on hook. (Busy tone supplied if
far-end station is busy.)
When call is answered, ringback tone is
removed , and call is cut through to far-end
station.
If near-end station hangs up first, the following
occurs: Line card detects drop in loop current.
High-
CPU removes timeslot assignments.
loop
Line card unit is ready for the next call.
If far-end station hangs up first, the following
occurs: Meridian 1 detects disconnect signaling
High- from trunk. CPU removes timeslot assignments.
Person at near-end station recognizes end of
call and hangs up.
loop
Line card unit is ready for the next call.
553-6146