Engaged Tones

There are two distinct types of engaged tone. There is the on-off repeating beep of constant length, which means that the line you are calling is engaged. If you hear this, generally, the line you are calling is in use.

The other engaged tone you will hear is a double beep, the first tone being twice as long as the second, and the second sometimes being perceptibly louder than the first. This means that the Exchange equipment is engaged, and your call cannot be routed. This tone is normally only heard on older exchanges, although it is more often being heard now where a "network interconnect" is busy.

Digital Dorothy

Digital Dorothy is the generic term for digital voice announcements. There are currently 2 in general use. "Sorry, Lines are busy" is the most often used. This means exactly the same as the Equipment Engaged tone; the exchange is busy and cannot route your call. It does not mean that the number you are calling is engaged, but that the lines between your exchange and that exchange are busy.

You may also hear "The number you are calling is temporarily unavailable" or "Sorry, there is a temporary fault". This means that, although there may be lines free to route your call, and lines free to take your call, your call has "collided" with one or more calls being routed to the same destination, and cannot be connected. You may get through if you redial immediately.

You may sometimes hear "There is currently a high demand for this location". This is an indication that call gapping is in place. Normally this means that a call ratio has been sent around the network, and calls to a destination are being failed at your exchange, to prevent the terminating exchange from being overloaded. Call gapping is often applied to 09x number used by TV shows. Gapping ratios used by the Telecom Networks go from 2:1 through to a worst case of 30:1 on some exchanges at New Year.

Call Gapping

It's an Open Secret that Telewest has applied Call Gapping to all of the blueyonder dialup numbers. Effectively, no exchange is allowed to connect more than 30 calls to any other exchange if it's a blueyonder PoP number. This means two things. Firstly, if you dial a PoP other than your local one, you are far less likely to get through and more likely to hit an engaged tone or Digital Dorothy message; and secondly, that you are less likely to get a good connection of you do get through.

Interconnect Errors

Some PoP numbers, although Telewest numbers, may be routed using a different telecom provider (NTL, C&W, BT, Eurobell). This is particularly relevant for Cable London, Cable Corporation, Yorkshire Cable and Eurobell customers. If you find yourself hitting "equipment engaged" tones, it is likely your call is failing because the other telco does not have sufficient capacity. Try a different PoP, preferably your local one.

Number Unobtainable

The NU tone can mean one of two things. On older exchanges, NU can mean that you have dialled a non-existent number, or that call gapping is in place on the number you have dialled. On newer exchanges, NU normally means that Digital Dorothy has failed... :-)

Summing Up

As you can see, all of the problems listed are telephony issues, with the exception of the "standard" engaged tone. If you ever get a standard engaged tone connecting to blueyonder, they want to know about it.

Otherwise, although they need to know about the other issues, they need to know exactly which message or tone you are getting, so that they can chase the correct department. They can only talk to their telecom provider (which is not always Telewest!) and ask them for an explanation of the problem. If you do the same, the problems will be resolved faster.

Last Amended : 2002-08-31 by elfin
Original Author : Doc Edison