NT1R20Off Premise Station (OPS) analog line card Page431 of 544
Option11C and 11C Mini Technical ReferenceGuide
Outgoing calls
For outgoing calls from a telephone, a line unit is seized when the telephone
goes off-hook, placing a low-resistance loop across the tip and ring leads
towards the OPS analog line card (see Table135 on page 431). When the card
detects the low-resistance loop, it prepares to receive digits. When the
Meridian 1 is ready to receive digits, it returns dial tone. Outward address
signaling is then applied from the telephone in the form of loop (interrupting)
dial pulses or DTMF tones.
Table 1 35
Call connection sequence—near-end station receiving call(Part 1 of 2)
State Signal/Direction
Far-endNear-end Remarks
Line card unit idle Group on tip, battery on ring
High resistance loop
No battery curre nt drawn.
Call request Low resistance l oop Near-end station goes off-hook. Battery
current is drawn, causing detection of
off-hook state.
Dial Tone Dial tone is applied to the near end
station from t he Option 11C.
Outpulsing Addressing signals Near-end station dials number (loop
pulsing or DTMF tones).
Option 11C detects start of dialing and
removes dial tone
Ringback (or busy) Option 11C decodes addressing, routes
call, and supplies ringback tone to near-
end station if far-end is on-hook. (Busy
tone is supplied if far-end is off-hook).
Two-way voice
connection
When call is answered, ringback tone is
removed, and call is put through to far-
end station.
Near-end station
hangs-up first
High resistance loop If near end station hangs-up first, the line
card detects the drop in loop current.
Line card unit idle Group on tip, battery on ring
High resistance loop
Line card unit is ready for the next call.