563489578934

574
Wire and Wireless Communication Applications Chap. 8
TABLE 8–1
TELEPHONE STANDARDS FOR THE SUBSCRIBER LOOP
Item
Standard
On hook (idle status)
Off hook (busy status)
Line open circuit, minimum DC resistance 30 kΩ
Line closed circuit, maximum DC resistance 200 Ω
Battery voltage
48 V
Operating current
20–80 mA, 40 mA typical
Subscriber-loop resistance
0–1300Ω, 3600Ω (max)
Loop loss
8 dB (typical), 17 dB (max)
Ringing voltage 90 V RMS, 20 Hz (typical) (usually pulsed on 2 s, off 4 s)
Ringer equivalence number (REN) a 0.2 REN (minimum), 5.0 REN (maximum)
Pulse dialing
Momentary open-circuit loop
Pulsing rate 10 pulses>
sec ;10%
Duty cycle
58–64% break (open)
Time between digits
600 ms minimum
Pulse code 1 pulse = 1, 2 pulses = 2, ..., 10 pulses = 0
Touch-tone b dialing
Level each tone
-6 to -4 dBm
Maximum difference in levels
4 dB
Maximum level (pair)
+2 dBm
Frequency tolerance ;1.5%
Pulse width
50 ms
Time between digits
45 ms minimum
Dial tone
Busy signal
Ringing signal tone
Caller ID c
Uses two tones, a low-frequency tone and a high-frequency
tone, to specify each digit:
High Tone (Hz)
Low Tone 1209 1336 1477
697 Hz 1 2 3
770 4 5 6
852 7 8 9
941 * 0 #
350 plus 440 Hz
480 plus 620 Hz, with 60 interruptions per minute
440 plus 480 Hz, 2 s on, 4 s off
1.2-kbit>
s FSK signal between first and second rings (Bell
202 modem standard) d
a Indicates the impedance loading caused by the telephone ringer. An REN of 1.0 equals about 8 kΩ, 0.2 REN equals 40 kΩ,
and 5.0 REN equals 1.6 kΩ.
b Touch tone was a registered trademark of AT&T. lt is also known as dual-tone multiple-frequency (DTMF) signaling.
c Other display services are also proposed [Schwartz, 1993].
d [Lancaster, 1991].