View source for Reorder tone

{{Short description|Audible signal indicating the call cannot be processed}}
{{listen
|filename=Reorder tone.ogg
|title=Example of a North American reorder tone
|description=Listen to a reorder tone from North America.
|filename2=1TR110-1 Kap8.5 Gassenbesetztton.ogg
|title2=Example of a European reorder tone
|description2=Listen to a reorder tone from Europe.
|filename3=UKReorderTone.ogg
|title3=Example of a British reorder tone
|description3=Listen to a reorder tone from the United Kingdom.}}
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.<ref name=nena />

The tone characteristics vary by country or telephone administrations. In North America it is a dual-[[frequency]] tone of 620&nbsp;Hz and 480&nbsp;Hz interrupted 120 times per minute at a cadence of 0.25 seconds on, 0.25 off, i.e., two beeps per second.

In EU countries and those following [[ETSI|ETSI (European Telecommunication Standards Institute)]] recommendations, the cadence is the same as North America, i.e. 0.25 seconds on / 0.25 seconds off, but with a 425&nbsp;Hz tone.

The UK reorder tone uses a 400&nbsp;Hz tone with a cadence of 0.4 seconds on, 0.35 seconds off, 0.225 seconds on, 0.525 seconds off. In some instances the Number Unobtainable Tone may be used instead. This is a continuous, uninterrupted 400&nbsp;Hz tone.

The signal is used to indicate that the destination is unreachable, either because all circuits (trunks) are busy, the called number is out of service, the call is unroutable, or sometimes that an invalid code has been dialed.<ref name=nena>{{cite web|url=http://www.nena.org/resource/resmgr/Standards/NENA_00-001_V16.pdf |title=NENA Master Glossary Of 9-1-1 Terminology |accessdate=2012-10-05 |publisher=National Emergency Number Association (NENA) |url-status=dead |archiveurl=https://web.archive.org/web/20120622070314/http://www.nena.org/resource/resmgr/Standards/NENA_00-001_V16.pdf |archivedate=June 22, 2012 }}</ref> A [[Private branch exchange|PBX]] also often indicates an invalid [[Extension (telephone)|extension]], while dialing an invalid [[telephone number]] on the PSTN usually results in playing the triple [[special information tone]] and a [[Intercept message|recorded announcement]].

Some European networks may return the reorder tone as a generic error signal for invalid or incorrect numbers or where a particular call type is not supported or has been barred.

Some switches, notably in Europe where open dial plans are used, analyse a number as it's dialled, and may even return a reorder tone before the complete number is dialled if the initial sequence of digits are invalid.

The reorder tone is sometimes confused with the [[busy signal]] because they use the same frequencies and differ only in that the busy signal's beeping sounds have a slower cadence than those of the reorder tone.

==References==
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{{telsigs}}

[[Category:Telephony signals]]


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