No dial tone but broadband still works - how?

[#1]

I have no dial tone on my phone service but broadband continues to work.  The Openreach engineer tells me that there is a break in the cable between the house and the pavement box.  I don't understand how the broadband continues to work if there is a break in the cable, or at least in one of the cores.  Can anyone explain please?

[#2]

don't always believe an Openreach engineer?!

[#3]

Broadband can actually work, after a fashion, with only one core working properly I believe whereas voice definitely doesn't

[#4]

Well he was correct, there are a lot of reports of broadband operating on just one wire, think the signal goes back via earth
Jim beat me to it

[#5]

It's RF - it jumps the gap.

[#6]

The replies are all correct
Broadband WILL work (though badly  -at a low sync ) if only one of the two wires in the incomming pair is connected.
(ie one wire is OK and the other has a break in it)
It does depend on which wire it is though!
I know  - I've had it happen to me.

[#7]

Quote from: x47c

It does depend on which wire it is though!

RF isn't polarity conscious is it?

[#8]

Exactly the same thing happened to me, I completely lost dial tone but maintained a broadband connection at a considerably reduced speed.  My problem was a bad connection.  I guess this was a join between two sections of wire that had become high resistance/impedance instead of very low resistance.  The broadband signal operates at high power and ADSL is designed to cope with a large impedance between the exchange and your house.  The telephone signal operates at relatively low power and expects a low impedance path. 

[#9]

Thanks for the replies.  Broadband download speed tests at a low 1Mbps and upload at 316kbps - until the line is repaired, I guess I should be thankful for small mercies!