Monday 31 December 2012

Mp3 Audio Songs

Mp3 Audio Songs Details
In old phones, this voltage was used to trigger a high-impedance electromagnet to ring a bell on the phone. Fixed phones of the late 20th century and later detect this ringing current voltage and trigger a warbling tone electronically. Mobile phones are fully digital, hence are signaled to ring as part of the protocol they use to communicate with the cell base stations.

In POTS switching systems, ringing is said to be "tripped" when the impedance of the line reduces to about 600 ohms when the telephone handset is lifted off the switch-hook. This signals that the telephone call has been answered, and the telephone exchange immediately removes the ringing signal from the line and connects the call. This is the source of the name of the problem called "ring-trip" or "pre-trip", which occurs when the ringing signal on the line encounters excessively low resistance between the conductors, which trips the ring before the subscriber's actual telephone has a chance to ring (for more than a very short time); this is common with wet connections and improperly installed lines.

Early research showed that people would wait until the phone stopped ringing before picking it up.[citation needed] Breaks were introduced into the signal to avoid this problem, resulting in the common ring-pause-ring cadence pattern used today. In early party line systems this pattern was a Morse code letter indicating who should pick up the phone, but today, with individual lines, the only surviving patterns are a single ring and double-ring, originally Morse code letters T (dash) and M (dash dash).[clarification needed]
The ringing pattern is known as ring cadence. This only applies to POTS fixed phones, where the high voltage ring signal is switched on and off to create the ringing pattern. In North America, the standard ring cadence is "2-4", or two seconds of ringing followed by four seconds of silence. In Australia and the UK, the standard ring cadence is 400 ms on, 200 ms off, 400 ms on, 2000 ms off. These patterns may vary from region to region, and other patterns are used in different countries around the world.
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