[PLUG-TALK] Known-good Touch Tone test service numbers?

Aaron Burt aaron at bavariati.org
Mon Feb 1 17:51:27 PST 2021


On 2021-02-01 16:11, Keith Lofstrom wrote:
> The testcall.com site I mentioned claimed to respond with
> a spoken numeral for the buttons pressed on the phone
> keypad.  It did not respond to many different analog phones
> plugged into two different outgoing POTS-to-digital lines.
<snip>

I tested it from my cellphone, dialing 804-222-1111.  After dialing 2 
for DTMF test, I punched in some digits and waited, and it read them 
back, then hung up on me.  So maybe your testing successfully failed. :)

DTMF over SIP is a bother.  Most digital VoIP devices default to using 
RFC 2833 signalling, and many analog telephone adaptors (ATAs) will try 
to interpret your phone's DTMF signals and then send them using RFC 
2833, where it says "do this DTMF tone" instead of actually just playing 
the sound.  Then the call termination side (e.g. whoever OOMA contracted 
with) plays those DTMF tones in short blips that are hard to detect.

Ever been talking with someone on the phone, and hear their voice cut 
out and a DTMF tone plays?  That's because "aaah" vowels sound like DTMF 
tones and some RFC 2833 gizmo is being overzealous.  My mom's 
long-distance service does that and it's kind of annoying.

If you control your own ATA, you can ensure that it's using a G.711 
u-law or G.729 codec and set it to inband DTMF instead of RFC 2833, and 
then your own phone's fine analog tones can pass through relatively 
unmolested.

For testing, you may need to just call some fellow telephony-nerd you 
know and start pushing buttons at them.

Regards,
   Aaron


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