TELECOM Digest OnLine - Sorted: Re: DTMF Sequences

Re: DTMF Sequences

Jack Hamilton (
Sat, 04 Mar 2006 19:25:08 -0800

sonali <> wrote:

> Hi all!

> I wanted to know what sequences are sent when we press * and #.

Touch tones are also known as DTMF, or dual-tone multi-frequency.
There are 4 "low" tones and 4 "high" tones. They combine, two at a
time, to create the 16 standard DTMF signals. There's no sequencing
involved in * and # - they're just two of the combinations.

The other 4 combinations, which you're not likely to have on your
phone, are A, B, C, and D. I have them on an amateur radio
Handi-Talkie, where they might be used to control radio repeaters.
They were originally intended for military use. See

> also, what sequences are sent for international calls? what happens
> when the sender tries to morph his identity ?what sequences are sent
> in such a case?

You may be thinking of trunk signaling, which I know nothing about.

Jack Hamilton

<> Qui vit sans folie n'est pas si sage qu'il croit.
<> François VI, duc de La Rochefoucauld

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