[asterisk-users] Alphabet character in destination number (CDR)

John Novack jnovack at comcast.net
Sat Apr 1 18:14:43 CDT 2017

J Montoya or A J Stiles wrote:
> On Thursday 30 Mar 2017, Ikka Tirtawidjaja wrote:
>> Dear all,
>> I have PBX with asterisk 13.x
>> a couple of IPPhone that connect to that asterisk PBX send an alphanumeric
>> dialed phone number.
>> for example, in my CDR table, field DST, it show dialed phone number like
>> - 0C81318304632C  (it should be 081318304632)
>> - 08D11157112 (it should be 0811157112).
>> Why it's happening ? and how can I prevent it to happen ?
> A, B, C and D are actually valid DTMF digits  (they belong in a column to the
> right of 3, 6, 9 and # respectively, and have the "high" frequency 1633 Hz).
> TTBOMK they were never actually used for anything in practice, they just keep
> kicking around like a vestigial organ  (compare how computer software for the
> UK financial industry still includes code to deal with mediaeval pounds,
> shillings and pence).
> Is it possible for a 1633 Hz tone, loud enough to swamp the "high" frequency
> of a dialled digit, to be finding its way somehow into the microphone of the
> affected phone and confusing it when digits are dialled?
A,BC & D were used in the US in the AutoVon Military system, and telephones that have that keypad often bring pretty good money.

Some external Voice mail systems use one or more of the codes as well ( Toshiba systems for one ) Probably because they are an easy way to prevent most users from messing around in the system
It was and in some cases still used for network signalling.
Not that computer telephony designers believe in standards but the 16 button tone pad is an ITU-T standard.  I believe in the UK it is known as MF-4

Asterisk DTMF detection leaves a lot to be desired. It certainly is not Exchange grade. There may be a way to diddle the code to remove the false detection but this should only happen with in-band signalling.I thought all SIP data was normally sent as data though sip.conf does allow in-band

John Novack


Dog is my Co-pilot

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