TELECOM Digest OnLine - Sorted: Re: DTMF Sequences

Re: DTMF Sequences

Gordon Burditt (
Sun, 05 Mar 2006 05:42:10 -0000

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

DTMF is not a sequence. It's a pair of frequencies sent down the
line. One frequency is selected from the row the key is in and the
other from the column on a standard dial layout:

1 2 3 A 697Hz
4 5 6 B 770Hz
7 8 9 C 852Hz
* 0 # D 941Hz

1209 1336 1477 1633
Hz Hz Hz Hz

Most phones do not have the ABCD column. On military phones it may be
labelled Flash Override, Flash, Immediate, and Priority. Some modems
let you dial A, B, C, or D. These codes are sometimes used for
controlling ham radio gateways to landline phones.

> what sequences are sent for international calls?

What do you dial for an international call? It's a sequence of
digits, each transmitted as a pair of frequencies. From the USA, this
is often 011 followed by the country code followed by the number.

> what happens when the
> sender tries to morph his identity ?

Caller-ID is not transmitted by DTMF. It is sent by modulation of the
same type used by a Bell 202 modem.

> what sequences are sent in such a case?

Gordon L. Burditt

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