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In the United Kingdom, the busy tone is a single 400 Hz tone with equal 0.375 s on/off periods. This was the case even when the UK was still part of the EU. The current 400 Hz/375ms tone was adopted in the mid-to-late 1960s and replaced the older busy tone, which was the same 400 Hz signal but at half the pulse duration, 0.75 s on, 0.75 s off.
The reorder tone, also known as the fast busy tone, or the congestion tone, or all trunks busy (ATB) tone is an audible call progress tone in the public switched telephone network (PSTN) that is returned to a calling party to indicate that the call cannot be processed through the network.
In the United Kingdom, a warbling signal sounding rather like an alarm siren is played at steadily increasing volume to a telephone left off-hook and unused on telephone lines provided by the BT Group and many PABX extensions. It is sometimes referred to as a howler. In some cases it is composed of the DTMF tones * and # played alternately.
Operator assistance refers to service provided by a telephone operator to the calling party of a telephone call.This can include telephone calls made from pay phones, calls placed station-to-station, person-to-person, or collect, third-number calls, calls billed to credit cards, and certain international calls which cannot be dialed directly.
In the past, the call would be forwarded to an intercept operator after usually two readings of the message; today, however, this procedure is not observed, and on some systems a fast busy signal follows the second reading of the message instead. (A busy or an Off-Hook may be used depending on the provider.)
For most of the 20th century, calls were usually placed on the public switched telephone network via electromechanical switching equipment.When a caller dialed a number that was busy or permanently unavailable, the central office of their carrier would shunt the incoming call to a circuit on which the busy signal tone was produced.
Even though represented as strings of letters, prosigns are rendered without the intercharacter commas or pauses that would occur between the letters shown, if the representation were (mistakenly) sent as a sequence of letters: In printed material describing their meaning and use, prosigns are shown either as a sequence of dots and dashes for the sound of a telegraph, or by an overlined ...
Call again, a form of automatic ring back, allows a caller, on reaching a busy signal, to hang up, dial a special code, and be called back automatically when the called number is no longer busy, usually with a limit of 30 minutes. Call return allows a customer to dial a code that identifies the last incoming call. On some types of central ...