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Page 168 of 894 NT1R20 Off-Premise Station Analog Line card
553-3001-211 Standard 2.00 September 2004
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 NT1R20 OPS analog line card (see Table 68 on page 168). When
the card detects the low-resistance loop, it prepares to receive digits. When
the system is ready to receive digits, it returns a dial tone. Outward address
signaling is then applied from the telephone in the form of loop (interrupting)
dial pulses or DTMF tones.
Far end station
hangs up first
High resistance loop If the far-end hangs-up first, the system
detects disconnect signalling from the
trunk. The person at the near-end
recognizes the end of the call and
hangs-up.
Line card unit idle Ground on tip/battery on ring
High resistance loop
Line card unit is ready for the next call.
Table 68
Call connection sequence—near-end station receiving call (Part 1 of 2)
State
Signal / Direction
Far-end / Near-end
Remarks
Line card unit idle Group on tip, battery on ring
High resistance loop
No battery current drawn.
Call request Low resistance loop 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 the system.
Table 67
Call connection sequence—near-end station receiving call (Part 2 of 2)
State
Signal / Direction
Far-end / Near-end
Remarks