[GLLUG] An obscure VOIP problem

James Dutton james.dutton at gmail.com
Sat Oct 8 21:46:13 UTC 2022

On Sat, 8 Oct 2022 at 17:44, Chris Bell via GLLUG
<gllug at mailman.lug.org.uk> wrote:
> Hello,
> My sister has direct FTTH with an Analogue Telephone Adapter provided by
> CommunityFibre.co.uk. She has dynamic IPv4 and dynamic IPv6 addresses.
> Almost everything works fine except when dialling a telephone number that
> requires a subsequent button press to select the required service. This always
> works or always fails, depending on the destination.
> She has a new Siemens Gigaset C570HX handset, C575A DECT base station, plus a
> pre-configured Grandstream HT801 Analogue Telephone Adapter (ATA) supplied by
> CommunityFibre.co.uk. There is a continuous internet data link from the ATA
> indicated by flashing LED's, but I do not know how the system sends the
> original DTMF. There is a suggestion that the DTMF might be converted and sent
> as digital codes by the ATA instead of audio tones, and converted back before
> being passed on to the current Public Service Telephone Network (Plain Old
> Telephone System, POTS), and might suffer corruption if the original DTMF is
> not completely removed first. The Siemens Gigaset equipment probably meets the
> precise DTMF requirements, but I have no control over the current VOIP system
> or the destination PABX.
> We are both long since retired and would prefer not to pay much higher charges
> for a business class connection, but I may have to choose a different VOIP
> supplier who can still retain her original telephone number.
> Any information and suggestions welcome. Thanks.
> --

The button press is passed across in a message and not a tone. The
tone is then recreated locally (sometimes) and remotely if needed.
The problem comes with the tone creation.
The tone might sound like it is a long tone locally, but it might be a
really short tone remotely.
When the tone is created from the message, any other audio on the line
is muted while the tone plays, so that no interference happens.
In summary, just try pressing the button on the handset for longer, so
the tone is longer. It normally fixes the problem.

If you can make calls, and hear the other person clearly, there is no
need to change ISP/CSP.

Kind Regards


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