Talk:Busy signal/Archives/2014

Subscriber line busy vs. trunk busy

It used to be, in the U.S. and Canada, that when you got a slower busy signal, it meant that the line for the individual subscriber number you dialed is busy, whereas at rapid busy signal meant that the trunk lines heading for the central office of the number you dialed were busy and you couldn't get trunk line through to the exchange you were dialing. I didn't want to post this information in the main article because I don't have enough specific data such as what the intervals of tone vs. no tone were for each of the two types of busy signal. Toddabearsf (talk) 18:39, 26 August 2013 (UTC)

There were actually more than just those two types. The standard "normal" (or "slow") busy tone (for the called line being in use) was equal on/off intervals of 0.5 sec. each, the same as today. There were two "fast busy" signals: One indicated toll circuit congestion and was 0.2 sec. on, 0.3 sec. off; the other was the local reorder tone, which was 0.3 sec. on, 0.2 sec. off. They sound subtly different, even if listened to individually many people might not have noticed. Local reorder was used to indicate insufficient paths through the local switching equipment, and often for invalid codes etc. Somewhere around the mid 1970's it was decided to do away with this distinction, and many tone plants installed after that time used a single "fast busy" with equal on/off periods of 0.25 sec. each.

At one time there was also another variation indicating long-distance toll circuits busy, which was 0.3 sec. on and 1.7 secs. off. This was later abandoned in favor of using the "fast" busy.

These were the main types used in North America, but non-standard cadences could be found in use in some places, e.g. a few very small offices had a single tone to serve as both line and toll busy, with a timing somewhere between the two standard cadences. 87.115.121.34 (talk) 16:45, 5 May 2014 (UTC)